* Symbol tables:: Symbol information in symbol tables
* Cplusplus:: Appendixes:
* Stab types:: Symbol types in a.out files
-* Symbol descriptors:: Table of Symbol descriptors
-* Type descriptors:: Table of Symbol descriptors
+* Symbol descriptors:: Table of symbol descriptors
+* Type descriptors:: Table of type descriptors
* Expanded reference:: Reference information by stab type
* Questions:: Questions and anomolies
* XCOFF differences:: Differences between GNU stabs in a.out
@menu
* Flow:: Overview of debugging information flow
* Stabs format:: Overview of stab format
-* String field:: The @code{.stabs} @var{string} field
+* String field:: The string field
* C example:: A simple example in C source
* Assembly code:: The simple example at the assembly level
@end menu
The overall format of each class of stab is:
@example
-.stabs "@var{string}",@var{type},0,@var{desc},@var{value}
-.stabn @var{type},0,@var{desc},@var{value}
-.stabd @var{type},0,@var{desc}
+.stabs "@var{string}",@var{type},@var{other},@var{desc},@var{value}
+.stabn @var{type},@var{other},@var{desc},@var{value}
+.stabd @var{type},@var{other},@var{desc}
.stabx "@var{string}",@var{value},@var{type},@var{sdb-type}
@end example
@code{n_strx} field is zero; see @ref{Symbol tables}). For
@code{.stabd}, the @var{value} field is implicit and has the value of
the current file location. For @code{.stabx}, the @var{sdb-type} field
-is unused for stabs and can always be set to zero.
+is unused for stabs and can always be set to zero. The @var{other}
+field is almost always unused and can be set to zero.
The number in the @var{type} field gives some basic information about
which type of stab this is (or whether it @emph{is} a stab, as opposed
in numeric order of the valid @var{type} field values for stab directives.
@node String field
-@section The @code{.stabs} @var{string} field
+@section The String Field
-For @code{.stabs} the @var{string} field holds the meat of the
-debugging information. The generally unstructured nature of this field
-is what makes stabs extensible. For some stab types the @var{string} field
+For most stabs the string field holds the meat of the
+debugging information. The flexible nature of this field
+is what makes stabs extensible. For some stab types the string field
contains only a name. For other stab types the contents can be a great
deal more complex.
-The overall format is of the @var{string} field is:
+The overall format of the string field for most stab types is:
@example
"@var{name}:@var{symbol-descriptor} @var{type-information}"
expense of speed.
@end table
-All of this can make the @var{string} field quite long. All
+All of this can make the string field quite long. All
versions of GDB, and some versions of dbx, can handle arbitrarily long
strings. But many versions of dbx cretinously limit the strings to
about 80 characters, so compilers which must work with such dbx's need
to split the @code{.stabs} directive into several @code{.stabs}
directives. Each stab duplicates exactly all but the
-@var{string} field. The @var{string} field of
+string field. The string field of
every stab except the last is marked as continued with a
double-backslash at the end. Removing the backslashes and concatenating
-the @var{string} fields of each stab produces the original,
+the string fields of each stab produces the original,
long string.
@node C example
@node Main program
@section Main program
-@deffn @code{.stabs} N_MAIN
@findex N_MAIN
Most languages allow the main program to have any name. The
@code{N_MAIN} stab type tells the debugger the name that is used in this
-program. Only the @var{string} field is significant; it is the name of
+program. Only the string field is significant; it is the name of
a function which is the main program. Most C compilers do not use this
stab (they expect the debugger to assume that the name is @code{main}),
but some C compilers emit an @code{N_MAIN} stab for the @code{main}
function.
-@end deffn
@node Source files
@section Paths and names of the source files
-@deffn @code{.stabs} N_SO
@findex N_SO
Before any other stabs occur, there must be a stab specifying the source
file. This information is contained in a symbol of stab type
-@code{N_SO}; the @var{string} field contains the name of the file. The
-@var{value} of the symbol is the start address of the portion of the
+@code{N_SO}; the string field contains the name of the file. The
+value of the symbol is the start address of the portion of the
text section corresponding to that file.
-With the Sun Solaris2 compiler, the @var{desc} field contains a
+With the Sun Solaris2 compiler, the desc field contains a
source-language code.
@c Do the debuggers use it? What are the codes? -djm
.text
Ltext0:
@end example
-@end deffn
Instead of @code{N_SO} symbols, XCOFF uses a @code{.file} assembler
directive which assembles to a standard COFF @code{.file} symbol;
XCOFF @code{C_BINCL} approach (which despite the similar name has little in
common with @code{N_BINCL}).
-@deffn @code{.stabs} N_SOL
@findex N_SOL
An @code{N_SOL} symbol specifies which include file subsequent symbols
-refer to. The @var{string} field is the name of the file and the
-@var{value} is the text address corresponding to the start of the
+refer to. The string field is the name of the file and the
+value is the text address corresponding to the start of the
previous include file and the start of this one. To specify the main
source file again, use an @code{N_SOL} symbol with the name of the main
source file.
-@end deffn
-@deffn @code{.stabs} N_BINCL
-@deffnx @code{.stabs} N_EINCL
-@deffnx {} N_EXCL
@findex N_BINCL
@findex N_EINCL
@findex N_EXCL
-On Suns, an @code{N_BINCL} symbol specifies the start of an include file.
-In an object file, only the @var{string} is significant; the Sun linker
-puts data into some of the other fields. The end of the include file is
-marked by an @code{N_EINCL} symbol (which has no @var{string} field). In
-an object file, there is no significant data in the @code{N_EINCL}
-symbol; the Sun linker puts data into some of the fields.
-@code{N_BINCL} and @code{N_EINCL} can be nested.
-
-If the linker detects that two source files have identical stabs with an
-@code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
+The @code{N_BINCL} approach works as follows. An @code{N_BINCL} symbol
+specifies the start of an include file. In an object file, only the
+string is significant; the Sun linker puts data into some of the
+other fields. The end of the include file is marked by an
+@code{N_EINCL} symbol (which has no string field). In an object
+file, there is no significant data in the @code{N_EINCL} symbol; the Sun
+linker puts data into some of the fields. @code{N_BINCL} and
+@code{N_EINCL} can be nested.
+
+If the linker detects that two source files have identical stabs between
+an @code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
for a header file), then it only puts out the stabs once. Each
additional occurance is replaced by an @code{N_EXCL} symbol. I believe
the Sun (SunOS4, not sure about Solaris) linker is the only one which
supports this feature.
@c What do the fields of N_EXCL contain? -djm
-@end deffn
-@deffn @code{.bi} C_BINCL
-@deffnx @code{.ei} C_EINCL
@findex C_BINCL
@findex C_EINCL
For the start of an include file in XCOFF, use the @file{.bi} assembler
directive, which generates a @code{C_BINCL} symbol. A @file{.ei}
directive, which generates a @code{C_EINCL} symbol, denotes the end of
the include file. Both directives are followed by the name of the
-source file in quotes, which becomes the @var{string} for the symbol.
-The @var{value} of each symbol, produced automatically by the assembler
+source file in quotes, which becomes the string for the symbol.
+The value of each symbol, produced automatically by the assembler
and linker, is the offset into the executable of the beginning
(inclusive, as you'd expect) or end (inclusive, as you would not expect)
of the portion of the COFF line table that corresponds to this include
file. @code{C_BINCL} and @code{C_EINCL} do not nest.
-@end deffn
@node Line numbers
@section Line numbers
-@deffn @code{.stabn} N_SLINE
@findex N_SLINE
An @code{N_SLINE} symbol represents the start of a source line. The
-@var{desc} field contains the line number and the @var{value} field
+desc field contains the line number and the value field
contains the code address for the start of that source line. On most
machines the address is absolute; for Sun's stabs-in-ELF, it is relative
to the function in which the @code{N_SLINE} symbol occurs.
-@end deffn
-@deffn @code{.stabn} N_DSLINE
-@deffnx @code{.stabn} N_BSLINE
@findex N_DSLINE
@findex N_BSLINE
GNU documents @code{N_DSLINE} and @code{N_BSLINE} symbols for line
to @code{N_SLINE} but are relocated differently by the linker. They
were intended to be used to describe the source location of a variable
declaration, but I believe that GCC2 actually puts the line number in
-the @var{desc} field of the stab for the variable itself. GDB has been
-ignoring these symbols (unless they contain a @var{string} field) since
+the desc field of the stab for the variable itself. GDB has been
+ignoring these symbols (unless they contain a string field) since
at least GDB 3.5.
-@end deffn
For single source lines that generate discontiguous code, such as flow
of control statements, there may be more than one line number entry for
start of each code range, each with the same line number.
XCOFF uses COFF line numbers, which are outside the scope of this
-document.
+document, ammeliorated by adequate marking of include files
+(@pxref{Include files}).
@node Procedures
@section Procedures
-@deffn @code{.stabs} N_FUN
@findex N_FUN
-All of the following stabs use the @code{N_FUN} symbol type.
+@findex N_FNAME
+@findex N_STSYM, for functions (Sun acc)
+@findex N_GSYM, for functions (Sun acc)
+All of the following stabs normally use the @code{N_FUN} symbol type.
+However, Sun's @code{acc} compiler on SunOS4 uses @code{N_GSYM} and
+@code{N_STSYM}, which means that the value of the stab for the function
+is useless and the debugger must get the address of the function from
+the non-stab symbols instead. BSD Fortran is said to use @code{N_FNAME}
+with the same restriction; the value of the symbol is not useful (I'm
+not sure it really does use this, because GDB doesn't handle this and no
+one has complained).
A function is represented by an @samp{F} symbol descriptor for a global
-(extern) function, and @samp{f} for a static (local) function. (The next
-@code{N_SLINE} symbol gives the line number of the start
-of the function.) The @var{value} field is the address of the start of the
-function (absolute for @code{a.out}; relative to the start of the file
-for Sun's stabs-in-ELF). The type information of the stab represents
-the return type of the function; thus @samp{foo:f5} means that foo is a
-function returning type 5.
-
-@c What determines whether the option here v is taken? -djm
-The type information of the stab is optionally followed by type
-information for each argument, with each argument preceded by @samp{;}.
-An argument type of 0 means that additional arguments are being passed,
-whose types and number may vary (@samp{...} in ANSI C). This extension
-is used by Sun's Solaris compiler. GDB has tolerated it (parsed the
-syntax, if not necessarily used the information) since at least version
-4.8; I don't know whether all versions of dbx tolerate it. The
-argument types given here are not redundant with the symbols for the
-arguments themselves (@pxref{Parameters}); they are the types of the
-arguments as they are passed, before any conversions might take place.
-For example, if a C function which is declared without a prototype takes
-a @code{float} argument, the value is passed as a @code{double} but then
-converted to a @code{float}. Debuggers need to use the types given in
-the arguments when printing values, but if calling the function they
-need to use the types given in the symbol defining the function.
-@c Are the "arguments themselves" referred to above the actual
-@c or formal parameters? I'm confused. -djm
+(extern) function, and @samp{f} for a static (local) function. The
+value field is the address of the start of the function (absolute
+for @code{a.out}; relative to the start of the file for Sun's
+stabs-in-ELF). The type information of the stab represents the return
+type of the function; thus @samp{foo:f5} means that foo is a function
+returning type 5. There is no need to try to get the line number of the
+start of the function from the stab for the function; it is in the next
+@code{N_SLINE} symbol.
+
+@c FIXME: verify whether the "I suspect" below is true or not.
+Some compilers (such as Sun's Solaris compiler) support an extension for
+specifying the types of the arguments. I suspect this extension is not
+used for old (non-prototyped) function definitions in C. If the
+extension is in use, the type information of the stab for the function
+is followed by type information for each argument, with each argument
+preceded by @samp{;}. An argument type of 0 means that additional
+arguments are being passed, whose types and number may vary (@samp{...}
+in ANSI C). GDB has tolerated this extension (parsed the syntax, if not
+necessarily used the information) since at least version 4.8; I don't
+know whether all versions of dbx tolerate it. The argument types given
+here are not redundant with the symbols for the formal parameters
+(@pxref{Parameters}); they are the types of the arguments as they are
+passed, before any conversions might take place. For example, if a C
+function which is declared without a prototype takes a @code{float}
+argument, the value is passed as a @code{double} but then converted to a
+@code{float}. Debuggers need to use the types given in the arguments
+when printing values, but when calling the function they need to use the
+types given in the symbol defining the function.
If the return type and types of arguments of a function which is defined
in another source file are specified (i.e., a function prototype in ANSI
These symbol descriptors are unusual in that they are not followed by
type information.
-Here is an exploded summary (with whitespace added for clarity):
-
-@example
-.stabs "@var{name}:
- @var{desc} @r{(global proc @samp{F})}
- @var{return_type_ref} @r{(int)}
- ",N_FUN, NIL, NIL,
- @var{address}
-@end example
-
-Going back to our ``hello world'' example program,
-
-@example
-48 ret
-49 restore
-@end example
-
-@noindent
-The @code{.stabs} entry after this code fragment shows the @var{name} of
-the procedure (@code{main}); the type descriptor @var{desc} (@code{F},
-for a global procedure); a reference to the predefined type @code{int}
-for the return type; and the starting @var{address} of the procedure.
+The following example shows a stab for a function @code{main} which
+returns type number @code{1}. The @code{_main} specified for the value
+is a reference to an assembler label which is used to fill in the start
+address of the function.
@example
-50 .stabs "main:F1",36,0,0,_main
+.stabs "main:F1",36,0,0,_main # @r{36 is N_FUN}
@end example
The stab representing a procedure is located immediately following the
group of other stabs describing elements of the procedure. These other
stabs describe the procedure's parameters, its block local variables, and
its block structure.
-@end deffn
@node Nested procedures
@section Nested procedures
-For any of the @code{N_FUN} symbol descriptors, after the symbol
-descriptor and the type information is optionally a scope specifier.
-This consists of a comma, the name of the procedure, another comma, and
-the name of the enclosing procedure. The first name is local to the
-scope specified, and seems to be redundant with the name of the symbol
-(before the @samp{:}). This feature is used by GCC, and presumably
-Pascal, Modula-2, etc., compilers, for nested functions.
+For any of the symbol descriptors representing procedures, after the
+symbol descriptor and the type information is optionally a scope
+specifier. This consists of a comma, the name of the procedure, another
+comma, and the name of the enclosing procedure. The first name is local
+to the scope specified, and seems to be redundant with the name of the
+symbol (before the @samp{:}). This feature is used by GCC, and
+presumably Pascal, Modula-2, etc., compilers, for nested functions.
If procedures are nested more than one level deep, only the immediately
containing scope is specified. For example, this code:
@node Block structure
@section Block structure
-@deffn @code{.stabn} N_LBRAC
-@deffnx @code{.stabn} N_RBRAC
@findex N_LBRAC
@findex N_RBRAC
The program's block structure is represented by the @code{N_LBRAC} (left
defined inside a block precede the @code{N_LBRAC} symbol for most
compilers, including GCC. Other compilers, such as the Convex, Acorn
RISC machine, and Sun @code{acc} compilers, put the variables after the
-@code{N_LBRAC} symbol. The @var{value} fields of the @code{N_LBRAC} and
+@code{N_LBRAC} symbol. The values of the @code{N_LBRAC} and
@code{N_RBRAC} symbols are the start and end addresses of the code of
the block, respectively. For most machines, they are relative to the
starting address of this source file. For the Gould NP1, they are
scope of a procedure are located after the @code{N_FUN} stab that
represents the procedure itself.
-Sun documents the @var{desc} field of @code{N_LBRAC} and
+Sun documents the desc field of @code{N_LBRAC} and
@code{N_RBRAC} symbols as containing the nesting level of the block.
-However, dbx seems to not care, and GCC always sets @var{desc} to
+However, dbx seems to not care, and GCC always sets desc to
zero.
-@end deffn
@node Constants
@chapter Constants
@dfn{automatic}), it can be allocated in a register (@pxref{Register
variables}) or on the stack.
-@deffn @code{.stabs} N_LSYM
@findex N_LSYM
-Each variable allocated on the stack has a stab of type @code{N_LSYM},
-with the symbol descriptor omitted. Since type information should begin
-with a digit, @samp{-}, or @samp{(}, only those characters precluded
-from being used for symbol descriptors. However, the Acorn RISC machine
-(ARM) is said to get this wrong: it puts out a mere type definition
-here, without the preceding @samp{@var{type-number}=}. This is a bad
-idea; there is no guarantee that type descriptors are distinct from
-symbol descriptors.
-
-The @var{value} of the stab is the offset of the variable within the
+Each variable allocated on the stack has a stab with the symbol
+descriptor omitted. Since type information should begin with a digit,
+@samp{-}, or @samp{(}, only those characters precluded from being used
+for symbol descriptors. However, the Acorn RISC machine (ARM) is said
+to get this wrong: it puts out a mere type definition here, without the
+preceding @samp{@var{type-number}=}. This is a bad idea; there is no
+guarantee that type descriptors are distinct from symbol descriptors.
+Stabs for stack variables use the @code{N_LSYM} stab type.
+
+The value of the stab is the offset of the variable within the
local variables. On most machines this is an offset from the frame
pointer and is negative. The location of the stab specifies which block
it is defined in; see @ref{Block structure}.
@xref{Procedures} for more information on the @code{N_FUN} stab, and
@ref{Block structure} for more information on the @code{N_LBRAC} and
@code{N_RBRAC} stabs.
-@end deffn
@node Global variables
@section Global variables
-@deffn @code{.stabs} N_GSYM
@findex N_GSYM
A variable whose scope is not specific to just one source file is
represented by the @samp{G} symbol descriptor. These stabs use the
from the external symbol for the global variable. In the example above,
the @code{.global _g_foo} and @code{_g_foo:} lines tell the assembler to
produce an external symbol.
-@end deffn
@node Register variables
@section Register variables
-@deffn @code{.stabn} N_RSYM
@findex N_RSYM
@c According to an old version of this manual, AIX uses C_RPSYM instead
@c of C_RSYM. I am skeptical; this should be verified.
Register variables have their own stab type, @code{N_RSYM}, and their
-own symbol descriptor, @samp{r}. The stab's @var{value} field contains the
+own symbol descriptor, @samp{r}. The stab's value field contains the
number of the register where the variable data will be stored.
@c .stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc)
@noindent
then the stab may be emitted at the end of the object file, with
the other bss symbols.
-@end deffn
@node Common blocks
@section Common blocks
referred to by several source files. It may contain several variables.
I believe Fortran is the only language with this feature.
-@deffn @code{.stabs} N_BCOMM
-@deffnx @code{.stabs} N_ECOMM
@findex N_BCOMM
@findex N_ECOMM
A @code{N_BCOMM} stab begins a common block and an @code{N_ECOMM} stab
ends it. The only field that is significant in these two stabs is the
-@var{string}, which names a normal (non-debugging) symbol that gives the
+string, which names a normal (non-debugging) symbol that gives the
address of the common block.
-@end deffn
-@deffn @code{.stabn} N_ECOML
@findex N_ECOML
Each stab between the @code{N_BCOMM} and the @code{N_ECOMM} specifies a
-member of that common block; its @var{value} is the offset within the
+member of that common block; its value is the offset within the
common block of that variable. The @code{N_ECOML} stab type is
documented for this purpose, but Sun's Fortran compiler uses
@code{N_GSYM} instead. The test case I looked at had a common block
local to a function and it used the @samp{V} symbol descriptor; I assume
one would use @samp{S} if not local to a function (that is, if a common
block @emph{can} be anything other than local to a function).
-@end deffn
@node Statics
@section Static variables
@c (although GCC
@c 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can
@c find the variables)
-@deffn @code{.stabs} N_STSYM
-@deffnx @code{.stabs} N_LCSYM
@findex N_STSYM
@findex N_LCSYM
In a.out files, @code{N_STSYM} means the data segment, @code{N_FUN}
@dots{}
.stabs "var_noinit:S1",40,0,0,_var_noinit # @r{40 is N_LCSYM}
@end example
-@end deffn
In XCOFF files, each symbol has a section number, so the stab type
need not indicate the segment.
@node Parameters
@section Parameters
-Actual parameters to a function are represented by a stab (or sometimes
+Formal parameters to a function are represented by a stab (or sometimes
two; see below) for each parameter. The stabs are in the order in which
the debugger should print the parameters (i.e., the order in which the
parameters are declared in the source file). The exact form of the stab
depends on how the parameter is being passed.
-@deffn @code{.stabs} N_PSYM
@findex N_PSYM
Parameters passed on the stack use the symbol descriptor @samp{p} and
-the @code{N_PSYM} symbol type. The @var{value} of the symbol is an offset
+the @code{N_PSYM} symbol type. The value of the symbol is an offset
used to locate the parameter on the stack; its exact meaning is
machine-dependent, but on most machines it is an offset from the frame
pointer.
The type definition of @code{argv} is interesting because it contains
several type definitions. Type 21 is pointer to type 2 (char) and
@code{argv} (type 20) is pointer to type 21.
-@end deffn
+
+@c FIXME: figure out what these mean and describe them coherently.
+The following are also said to go with @code{N_PSYM}:
+
+@example
+"name" -> "param_name:#type"
+ -> pP (<<??>>)
+ -> pF Fortran function parameter
+ -> X (function result variable)
+ -> b (based variable)
+
+value -> offset from the argument pointer (positive).
+@end example
@menu
* Register parameters::
Debuggers use the second one to find the value, and the first one to
know that it is an argument.
-@deffn @code{.stabs} C_RPSYM
@findex C_RPSYM
+@findex N_RSYM, for parameters
Because that approach is kind of ugly, some compilers use symbol
descriptor @samp{P} or @samp{R} to indicate an argument which is in a
register. Symbol type @code{C_RPSYM} is used with @samp{R} and
-@code{N_RSYM} is used with @samp{P}. The symbol @var{value} field is
+@code{N_RSYM} is used with @samp{P}. The symbol's value field is
the register number. @samp{P} and @samp{R} mean the same thing; the
difference is that @samp{P} is a GNU invention and @samp{R} is an IBM
(XCOFF) invention. As of version 4.9, GDB should handle either one.
-@end deffn
There is at least one case where GCC uses a @samp{p} and @samp{r} pair
rather than @samp{P}; this is where the argument is passed in the
indicates that it's a floating point register? I haven't verified
whether the system actually does what the documentation indicates.
+@c FIXME: On the hppa this is for any type > 8 bytes, I think, and not
+@c for small structures (investigate).
On the sparc and hppa, for a @samp{P} symbol whose type is a structure
or union, the register contains the address of the structure. On the
sparc, this is also true of a @samp{p} and @samp{r} pair (using Sun
stores it as a local variable. If possible, the compiler should claim
that it's in a register, but this isn't always done.
+@findex N_LSYM, for parameter
Some compilers use the pair of symbols approach described above
(@samp{@var{arg}:p} followed by @samp{@var{arg}:}); this includes GCC1
(not GCC2) on the sparc when passing a small structure and GCC2
and the type of the @samp{@var{arg}:} symbol is @code{float}). GCC, at
least on the 960, uses a single @samp{p} symbol descriptor for an
argument which is stored as a local variable but uses @code{N_LSYM}
-instead of @code{N_PSYM}. In this case, the @var{value} of the symbol
+instead of @code{N_PSYM}. In this case, the value of the symbol
is an offset relative to the local variables for that function, not
relative to the arguments; on some machines those are the same thing,
but not on all.
languages, in which the size of an array parameter is not known to the
called function until run-time. Such parameters have two stabs: a
@samp{x} for the array itself, and a @samp{C}, which represents the size
-of the array. The @var{value} of the @samp{x} stab is the offset in the
+of the array. The value of the @samp{x} stab is the offset in the
argument list where the address of the array is stored (it this right?
-it is a guess); the @var{value} of the @samp{C} stab is the offset in the
+it is a guess); the value of the @samp{C} stab is the offset in the
argument list where the size of the array (in elements? in bytes?) is
stored.
big to describe in an @code{int}. Traditionally this is only used for
@code{unsigned int} and @code{unsigned long}:
-@c FIXME: Update this for the 2.4.5 output, not 2.3.3
@example
.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
-.stabs "long long int:t7=r1;0;-1;",128,0,0,0
@end example
-For larger types, GCC
-2.4.5 puts out bounds in octal, with a leading 0. In this case a
-negative bound consists of a number which is a 1 bit followed by a bunch
-of 0 bits, and a positive bound is one in which a bunch of bits are 1.
-All known versions of dbx and GDB version 4 accept this, but GDB 3.5
-refuses to read the whole file containing such symbols. So GCC 2.3.3
-did not output the proper size for these types.
+For larger types, GCC 2.4.5 puts out bounds in octal, with a leading 0.
+In this case a negative bound consists of a number which is a 1 bit
+followed by a bunch of 0 bits, and a positive bound is one in which a
+bunch of bits are 1. All known versions of dbx and GDB version 4 accept
+this, but GDB 3.5 refuses to read the whole file containing such
+symbols. So GCC 2.3.3 did not output the proper size for these types.
+@c FIXME: How about an example?
If the lower bound of a subrange is 0 and the upper bound is negative,
the type is an unsigned integral type whose size in bytes is the
precision? Double precison?).
@item 6 (NF_LDOUBLE)
-@code{long double}. This should probably only be used for Sun format
+Long double. This should probably only be used for Sun format
@code{long double}, and new codes should be used for other floating
point formats (@code{NF_DOUBLE} can be used if a @code{long double} is
really just an IEEE double, of course).
@node Miscellaneous types
@section Miscellaneous types
-These type descriptors are for types that are built into languages and
-are derived from the fundamental types.
-
@table @code
@item b @var{type-information} ; @var{bytes}
Pascal space type. This is documented by IBM; what does it mean?
always a digit, @samp{(}, or @samp{-}.
@item B @var{type-information}
-A @code{volatile}-qualified version of @var{type-information}. This is
+A volatile-qualified version of @var{type-information}. This is
a Sun extension. References and stores to a variable with a
-@code{volatile}-qualified type must not be optimized or cached; they
+volatile-qualified type must not be optimized or cached; they
must occur as the user specifies them.
@item d @var{type-information}
by Pascal.
@item k @var{type-information}
-A @code{const}-qualified version of @var{type-information}. This is a
-Sun extension. A variable with a @code{const}-qualified type cannot be
-modified.
+A const-qualified version of @var{type-information}. This is a Sun
+extension. A variable with a const-qualified type cannot be modified.
@item M @var{type-information} ; @var{length}
Multiple instance type. The type seems to composed of @var{length}
dimensional array. According to AIX documentation, the element type
must be type information. GDB accepts either.
-The type of the index is often a range type, expressed as the letter @samp{r}
-and some parameters. It defines the size of the array. In the example
-below, the range @samp{r1;0;2;} defines an index type which is a
-subrange of type 1 (integer), with a lower bound of 0 and an upper bound
-of 2. This defines the valid range of subscripts of a three-element C
-array.
+The type of the index is often a range type, expressed as the type
+descriptor @samp{r} and some parameters. It defines the size of the
+array. In the example below, the range @samp{r1;0;2;} defines an index
+type which is a subrange of type 1 (integer), with a lower bound of 0
+and an upper bound of 2. This defines the valid range of subscripts of
+a three-element C array.
For example, the definition:
following the @samp{22=} of the type definition narrows it down to an
enumeration type. Following the @samp{e} is a list of the elements of
the enumeration. The format is @samp{@var{name}:@var{value},}. The
-list of elements ends with a @samp{;}.
+list of elements ends with @samp{;}.
There is no standard way to specify the size of an enumeration type; it
is determined by the architecture (normally all enumerations types are
The structure tag has an @code{N_LSYM} stab type because, like the
enumeration, the symbol has file scope. Like the enumeration, the
symbol descriptor is @samp{T}, for enumeration, structure, or tag type.
-The symbol descriptor @samp{s} following the @samp{16=} of the type
+The type descriptor @samp{s} following the @samp{16=} of the type
definition narrows the symbol type to structure.
-Following the structure symbol descriptor is the number of bytes the
+Following the @samp{s} type descriptor is the number of bytes the
structure occupies, followed by a description of each structure element.
The structure element descriptions are of the form @var{name:type, bit
offset from the start of the struct, number of bits in the element}.
-@display
-.stabs "name:sym_desc(struct tag) Type_def(16)=type_desc(struct type)
- struct_bytes
- elem_name:type_ref(int),bit_offset,field_bits;
- elem_name:type_ref(float),bit_offset,field_bits;
- elem_name:type_def(17)=type_desc(array)
- index_type(range of int from 0 to 7);
- element_type(char),bit_offset,field_bits;;",
- N_LSYM,NIL,NIL,NIL
-@end display
-
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@example
+# @r{128 is N_LSYM}
.stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
@end example
For example,
@example
-.stabs "s_typedef:t16",128,0,0,0
+.stabs "s_typedef:t16",128,0,0,0 # @r{128 is N_LSYM}
@end example
specifies that @code{s_typedef} refers to type number 16. Such stabs
-have symbol type @code{N_LSYM} (or @code{C_DECL} on AIX).
+have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF).
If you are specifying the tag name for a structure, union, or
enumeration, use the @samp{T} symbol descriptor instead. I believe C is
for @code{u_type} do not convey any infomation about its procedure local
scope.
-@display
-.stabs "name:sym_desc(union tag)type_def(22)=type_desc(union)
- byte_size(4)
- elem_name:type_ref(int),bit_offset(0),bit_size(32);
- elem_name:type_ref(float),bit_offset(0),bit_size(32);
- elem_name:type_ref(ptr to char),bit_offset(0),bit_size(32);;"
- N_LSYM, NIL, NIL, NIL
-@end display
-
+@c FIXME: phony line break. Can probably be fixed by using an example
+@c with fewer fields.
@smallexample
+# @r{128 is N_LSYM}
.stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
128,0,0,0
@end smallexample
The stab for the union variable is:
-@display
-.stabs "name:type_ref(u_tag)", N_LSYM, NIL, NIL, frame_ptr_offset
-@end display
-
@example
-.stabs "an_u:23",128,0,0,-20
+.stabs "an_u:23",128,0,0,-20 # @r{128 is N_LSYM}
@end example
+@samp{-20} specifies where the variable is stored (@pxref{Stack
+variables}).
+
@node Function types
@section Function types
@samp{R} type descriptors.
First comes the type descriptor. If it is @samp{f} or @samp{F}, this
-type involves a function, and the type information for the return type
-of the function follows, followed by a comma. Then comes the number of
-parameters to the function and a semicolon. Then, for each parameter,
-there is the name of the parameter followed by a colon (this is only
-present for type descriptors @samp{R} and @samp{F} which represent
-Pascal function or procedure parameters), type information for the
-parameter, a comma, 0 if passed by reference or 1 if passed by value,
-and a semicolon. The type definition ends with a semicolon.
+type involves a function rather than a procedure, and the type
+information for the return type of the function follows, followed by a
+comma. Then comes the number of parameters to the function and a
+semicolon. Then, for each parameter, there is the name of the parameter
+followed by a colon (this is only present for type descriptors @samp{R}
+and @samp{F} which represent Pascal function or procedure parameters),
+type information for the parameter, a comma, 0 if passed by reference or
+1 if passed by value, and a semicolon. The type definition ends with a
+semicolon.
For example, this variable definition:
Each time the assembler encounters a stab directive, it puts
each field of the stab into a corresponding field in a symbol table
-entry of its output file. If the stab contains a @var{string} field, the
+entry of its output file. If the stab contains a string field, the
symbol table entry for that stab points to a string table entry
containing the string data from the stab. Assembler labels become
relocatable addresses. Symbol table entries in a.out have the format:
@};
@end example
-For @code{.stabs} directives, the @code{n_strx} field holds the offset
-in bytes from the start of the string table to the string table entry
-containing the @var{string} field. For other classes of stabs
-(@code{.stabn} and @code{.stabd}) this field is zero.
+If the stab has a string, the @code{n_strx} field holds the offset in
+bytes of the string within the string table. The string is terminated
+by a NUL character. If the stab lacks a string (for example, it was
+produced by a @code{.stabn} or @code{.stabd} directive), the
+@code{n_strx} field is zero.
Symbol table entries with @code{n_type} field values greater than 0x1f
originated as stabs generated by the compiler (with one random
assembler and linker symbols, the columns are: @var{value}, @var{type},
@var{string}.
-Where the @var{value} field of a stab contains a frame pointer offset,
-or a register number, that @var{value} is unchanged by the rest of the
-build.
+The low 5 bits of the stab type tell the linker how to relocate the
+value of the stab. Thus for stab types like @code{N_RSYM} and
+@code{N_LSYM}, where the value is an offset or a register number, the
+low 5 bits are @code{N_ABS}, which tells the linker not to relocate the
+value.
-Where the @var{value} field of a stab contains an assembly language label,
+Where the value of a stab contains an assembly language label,
it is transformed by each build step. The assembler turns it into a
relocatable address and the linker turns it into an absolute address.
file (see below). The first one originated as a stab. The second one
is an external symbol. The upper case @samp{D} signifies that the
@code{n_type} field of the symbol table contains 7, @code{N_DATA} with
-local linkage. The @var{value} field is empty for the stab entry. For
+local linkage. The value field is empty for the stab entry. For
the linker symbol, it contains the relocatable address corresponding to
the variable.
@node Stab types
@appendix Table of stab types
-The following are all the possible values for the stab @var{type} field, for
-@code{a.out} files, in numeric order. This does not apply to XCOFF.
+The following are all the possible values for the stab type field, for
+@code{a.out} files, in numeric order. This does not apply to XCOFF, but
+it does apply to stabs in ELF. Stabs in ECOFF use these values but add
+0x8f300 to distinguish them from non-stab symbols.
The symbolic names are defined in the file @file{include/aout/stabs.def}.
Global symbol; see @ref{Global variables}.
@item 0x22 N_FNAME
-Function name (for BSD Fortran); see @ref{N_FNAME}.
+Function name (for BSD Fortran); see @ref{Procedures}.
@item 0x24 N_FUN
Function name (@pxref{Procedures}) or text segment variable
@node Symbol descriptors
@appendix Table of symbol descriptors
-These tell in the @code{.stabs} @var{string} field what kind of symbol
-the stab represents. They follow the colon which follows the symbol
-name. @xref{String field}, for more information about their use.
+The symbol descriptor is the character which follows the colon in many
+stabs, and which tells what kind of stab it is. @xref{String field},
+for more information about their use.
@c Please keep this alphabetical
@table @code
Constant; see @ref{Constants}.
@item C
-Conformant array bound (Pascal, maybe other languages); @ref{Reference
-parameters}. Name of a caught exception (GNU C++). These can be
+Conformant array bound (Pascal, maybe other languages); @ref{Conformant
+arrays}. Name of a caught exception (GNU C++). These can be
distinguished because the latter uses @code{N_CATCH} and the former uses
another symbol type.
@node Type descriptors
@appendix Table of type descriptors
-These tell in the @code{.stabs} @var{string} field what kind of type is being
-defined. They follow the type number and an equals sign.
+The type descriptor is the character which follows the type number and
+an equals sign. It specifies what kind of type is being defined.
@xref{String field}, for more information about their use.
@table @code
Finally, any further information.
@menu
-* N_FNAME:: Function name (BSD Fortran)
* N_PC:: Pascal global symbol
* N_NSYMS:: Number of symbols
* N_NOMAP:: No DST map
* N_LENG:: Length of preceding entry
@end menu
-@node N_FNAME
-@section N_FNAME
-
-@deffn @code{.stabs} N_FNAME
-@findex N_FNAME
-Function name (for BSD Fortran).
-
-@example
-"name" -> "function_name"
-@end example
-
-Only the @var{string} field is significant. The location of the symbol is
-obtained from the corresponding extern symbol.
-@end deffn
-
@node N_PC
@section N_PC
<<?>>
"path to associated @file{.cb} file"
-Note: @var{type} field value overlaps with N_BSLINE.
+Note: N_BROWS has the same value as N_BSLINE.
@end deffn
@node N_DEFD
@findex N_DEFD
GNU Modula2 definition module dependency.
-GNU Modula-2 definition module dependency. @var{value} is the modification
-time of the definition file. @var{other} is non-zero if it is imported with
-the GNU M2 keyword @code{%INITIALIZE}. Perhaps @code{N_M2C} can be used
-if there are enough empty fields?
+GNU Modula-2 definition module dependency. The value is the
+modification time of the definition file. The other field is non-zero
+if it is imported with the GNU M2 keyword @code{%INITIALIZE}. Perhaps
+@code{N_M2C} can be used if there are enough empty fields?
@end deffn
@node N_EHDECL
@findex N_CATCH
GNU C++ @code{catch} clause
-GNU C++ @code{catch} clause. @code{value} is its address. @code{desc}
+GNU C++ @code{catch} clause. The value is its address. The desc field
is nonzero if this entry is immediately followed by a @code{CAUGHT} stab
saying what exception was caught. Multiple @code{CAUGHT} stabs means
-that multiple exceptions can be caught here. If @code{desc} is 0, it
-means all exceptions are caught here.
+that multiple exceptions can be caught here. If desc is 0, it means all
+exceptions are caught here.
@end deffn
@node N_SSYM
@findex N_SSYM
Structure or union element.
-@code{value} is offset in the structure.
+The value is the offset in the structure.
<<?looking at structs and unions in C I didn't see these>>
@end deffn
@deffn @code{.stabn} N_ENTRY
@findex N_ENTRY
Alternate entry point.
-@code{value} is its address.
+The value is its address.
<<?>>
@end deffn
@deffn @code{.stabn} N_LENG
@findex N_LENG
Second symbol entry containing a length-value for the preceding entry.
-The @var{value} is the length.
+The value is the length.
@end deffn
@node Questions
@item
@c I think this is changed in GCC 2.4.5 to put the line number there.
For GNU C stabs defining local and global variables (@code{N_LSYM} and
-@code{N_GSYM}), the @var{desc} field is supposed to contain the source
-line number on which the variable is defined. In reality the @var{desc}
+@code{N_GSYM}), the desc field is supposed to contain the source
+line number on which the variable is defined. In reality the desc
field is always 0. (This behavior is defined in @file{dbxout.c} and
-putting a line number in @var{desc} is controlled by @samp{#ifdef
+putting a line number in desc is controlled by @samp{#ifdef
WINNING_GDB}, which defaults to false). GDB supposedly uses this
information if you say @samp{list @var{var}}. In reality, @var{var} can
be a variable defined in the program and GDB says @samp{function
stab type storage class
-------------------------------
N_GSYM C_GSYM
-N_FNAME unknown
+N_FNAME unused
N_FUN C_FUN
N_STSYM C_STSYM
N_LCSYM C_STSYM
-N_MAIN unkown
+N_MAIN unknown
N_PC unknown
N_RSYM C_RSYM
unknown C_RPSYM
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