@end ifset
@c man end
-@ifinfo
-@format
-START-INFO-DIR-ENTRY
+@ifnottex
+@dircategory Software development
+@direntry
* Ld: (ld). The GNU linker.
-END-INFO-DIR-ENTRY
-@end format
-@end ifinfo
+@end direntry
+@end ifnottex
@copying
This file documents the @sc{gnu} linker LD
@end ifset
version @value{VERSION}.
-Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
+Copyright @copyright{} 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
@vskip 0pt plus 1filll
@c man begin COPYRIGHT
-Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001,
-2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+Copyright @copyright{} 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free
+Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
@kindex --nmagic
@item -n
@itemx --nmagic
-Turn off page alignment of sections, and mark the output as
-@code{NMAGIC} if possible.
+Turn off page alignment of sections, and disable linking against shared
+libraries. If the output format supports Unix style magic numbers,
+mark the output as @code{NMAGIC}.
@kindex -N
@kindex --omagic
@item --as-needed
@itemx --no-as-needed
This option affects ELF DT_NEEDED tags for dynamic libraries mentioned
-on the command line after the @option{--as-needed} option. Normally,
+on the command line after the @option{--as-needed} option. Normally
the linker will add a DT_NEEDED tag for each dynamic library mentioned
on the command line, regardless of whether the library is actually
-needed. @option{--as-needed} causes a DT_NEEDED tag to only be emitted
-for a library that satisfies a symbol reference from regular objects
-which is undefined at the point that the library was linked, or, if
-the library is not found in the DT_NEEDED lists of other libraries
-linked up to that point, a reference from another dynamic library.
+needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be
+emitted for a library that satisfies an undefined symbol reference
+from a regular object file or, if the library is not found in the
+DT_NEEDED lists of other libraries linked up to that point, an
+undefined symbol reference from another dynamic library.
@option{--no-as-needed} restores the default behaviour.
@kindex --add-needed
@kindex --no-add-needed
@item --add-needed
@itemx --no-add-needed
-This option affects the treatment of dynamic libraries from ELF
-DT_NEEDED tags in dynamic libraries mentioned on the command line after
-the @option{--no-add-needed} option. Normally, the linker will add
-a DT_NEEDED tag for each dynamic library from DT_NEEDED tags.
-@option{--no-add-needed} causes DT_NEEDED tags will never be emitted
-for those libraries from DT_NEEDED tags. @option{--add-needed} restores
-the default behaviour.
+These two options have been deprecated because of the similarity of
+their names to the @option{--as-needed} and @option{--no-as-needed}
+options. They have been replaced by @option{--copy-dt-needed-entries}
+and @option{--no-copy-dt-needed-entries}.
@kindex -assert @var{keyword}
@item -assert @var{keyword}
force checking in that case by using the @option{--check-sections}
option.
+@kindex --copy-dt-needed-entries
+@kindex --no-copy-dt-needed-entries
+@item --copy-dt-needed-entries
+@itemx --no-copy-dt-needed-entries
+This option affects the treatment of dynamic libraries referred to
+by DT_NEEDED tags @emph{inside} ELF dynamic libraries mentioned on the
+command line. Normally the linker will add a DT_NEEDED tag to the
+output binary for each library mentioned in a DT_NEEDED tag in an
+input dynamic library. With @option{--no-copy-dt-needed-entries}
+specified on the command line however any dynamic libraries that
+follow it will have their DT_NEEDED entries ignored. The default
+behaviour can be restored with @option{--copy-dt-needed-entries}.
+
+This option also has an effect on the resolution of symbols in dynamic
+libraries. With the default setting dynamic libraries mentioned on
+the command line will be recursively searched, following their
+DT_NEEDED tags to other libraries, in order to resolve symbols
+required by the output binary. With
+@option{--no-copy-dt-needed-entries} specified however the searching
+of dynamic libraries that follow it will stop with the dynamic
+library itself. No DT_NEEDED links will be traversed to resolve
+symbols.
+
@cindex cross reference table
@kindex --cref
@item --cref
relocations. See @samp{--entry} and @samp{--undefined}.
This option can be set when doing a partial link (enabled with option
-@samp{-r}). In this case the root of symbols kept must be explicitely
+@samp{-r}). In this case the root of symbols kept must be explicitly
specified either by an @samp{--entry} or @samp{--undefined} option or by
a @code{ENTRY} command in the linker script.
@kindex --relax
@cindex synthesizing linker
@cindex relaxing addressing modes
+@cindex --no-relax
@item --relax
+@itemx --no-relax
An option with machine dependent effects.
@ifset GENERIC
This option is only supported on a few targets.
@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
@end ifset
-On some platforms, the @samp{--relax} option performs global
-optimizations that become possible when the linker resolves addressing
-in the program, such as relaxing address modes and synthesizing new
-instructions in the output object file.
+On some platforms the @samp{--relax} option performs target specific,
+global optimizations that become possible when the linker resolves
+addressing in the program, such as relaxing address modes,
+synthesizing new instructions, selecting shorter version of current
+instructions, and combinig constant values.
On some platforms these link time global optimizations may make symbolic
debugging of the resulting executable impossible.
@ifset GENERIC
-This is known to be
-the case for the Matsushita MN10200 and MN10300 family of processors.
+This is known to be the case for the Matsushita MN10200 and MN10300
+family of processors.
@end ifset
@ifset GENERIC
but ignored.
@end ifset
+On platforms where @samp{--relax} is accepted the option
+@samp{--no-relax} can be used to disable the feature.
+
@cindex retaining specified symbols
@cindex stripping all but some symbols
@cindex symbols, retaining selectively
mismatches are considered to be errors.
[This option is specific to the i386 PE targeted port of the linker]
+@kindex --leading-underscore
+@kindex --no-leading-underscore
+@item --leading-underscore
+@itemx --no-leading-underscore
+For most targets default symbol-prefix is an underscore and is defined
+in target's description. By this option it is possible to
+disable/enable the default underscore symbol-prefix.
+
@cindex DLLs, creating
@kindex --export-all-symbols
@item --export-all-symbols
exported. The symbol names may be delimited by commas or colons.
[This option is specific to the i386 PE targeted port of the linker]
+@kindex --exclude-all-symbols
+@item --exclude-all-symbols
+Specifies no symbols should be automatically exported.
+[This option is specific to the i386 PE targeted port of the linker]
+
@kindex --file-alignment
@item --file-alignment
Specify the file alignment. Sections in the file will always begin at
@item
the @code{ENTRY(@var{symbol})} command in a linker script;
@item
-the value of the symbol @code{start}, if defined;
+the value of a target specific symbol, if it is defined; For many
+targets this is @code{start}, but PE and BeOS based systems for example
+check a list of possible entry symbols, matching the first one found.
@item
the address of the first byte of the @samp{.text} section, if present;
@item
architecture of an object file by using the @code{objdump} program with
the @samp{-f} option.
@end ifclear
+
+@item LD_FEATURE(@var{string})
+@kindex LD_FEATURE(@var{string})
+This command may be used to modify @command{ld} behavior. If
+@var{string} is @code{"SANE_EXPR"} then absolute symbols and numbers
+in a script are simply treated as numbers everywhere.
+@xref{Expression Section}.
@end table
@node Assignments
@cindex address, section
@cindex section address
The @var{address} is an expression for the VMA (the virtual memory
-address) of the output section. If you do not provide @var{address},
-the linker will set it based on @var{region} if present, or otherwise
-based on the current value of the location counter.
-
-If you provide @var{address}, the address of the output section will be
-set to precisely that. If you provide neither @var{address} nor
-@var{region}, then the address of the output section will be set to the
-current value of the location counter aligned to the alignment
-requirements of the output section. The alignment requirement of the
-output section is the strictest alignment of any input section contained
-within the output section.
-
-For example,
+address) of the output section. This address is optional, but if it
+is provided then the output address will be set exactly as specified.
+
+If the output address is not specified then one will be chosen for the
+section, based on the heuristic below. This address will be adjusted
+to fit the alignment requirement of the output section. The
+alignment requirement is the strictest alignment of any input section
+contained within the output section.
+
+The output section address heuristic is as follows:
+
+@itemize @bullet
+@item
+If an output memory @var{region} is set for the section then it
+is added to this region and its address will be the next free address
+in that region.
+
+@item
+If the MEMORY command has been used to create a list of memory
+regions then the first region which has attributes compatible with the
+section is selected to contain it. The section's output address will
+be the next free address in that region; @ref{MEMORY}.
+
+@item
+If no memory regions were specified, or none match the section then
+the output address will be based on the current value of the location
+counter.
+@end itemize
+
+@noindent
+For example:
+
@smallexample
.text . : @{ *(.text) @}
@end smallexample
+
@noindent
and
+
@smallexample
.text : @{ *(.text) @}
@end smallexample
+
@noindent
are subtly different. The first will set the address of the
@samp{.text} output section to the current value of the location
counter. The second will set it to the current value of the location
-counter aligned to the strictest alignment of a @samp{.text} input
-section.
+counter aligned to the strictest alignment of any of the @samp{.text}
+input sections.
The @var{address} may be an arbitrary expression; @ref{Expressions}.
For example, if you want to align the section on a 0x10 byte boundary,
difference is @code{SORT_BY_ALIGNMENT} will sort sections into
ascending order by alignment before placing them in the output file.
+@cindex SORT_BY_INIT_PRIORITY
+@code{SORT_BY_INIT_PRIORITY} is very similar to @code{SORT_BY_NAME}. The
+difference is @code{SORT_BY_INIT_PRIORITY} will sort sections into
+ascending order by numerical value of the GCC init_priority attribute
+encoded in the section name before placing them in the output file.
+
@cindex SORT
@code{SORT} is an alias for @code{SORT_BY_NAME}.
the input sections which map into it. You can override this by using
the section type. For example, in the script sample below, the
@samp{ROM} section is addressed at memory location @samp{0} and does not
-need to be loaded when the program is run. The contents of the
-@samp{ROM} section will appear in the linker output file as usual.
+need to be loaded when the program is run.
@smallexample
@group
SECTIONS @{
@cindex load address
@cindex section load address
Every section has a virtual address (VMA) and a load address (LMA); see
-@ref{Basic Script Concepts}. The address expression which may appear in
-an output section description sets the VMA (@pxref{Output Section
-Address}).
+@ref{Basic Script Concepts}. The virtual address is specified by the
+@pxref{Output Section Address} described earlier. The load address is
+specified by the @code{AT} or @code{AT>} keywords. Specifying a load
+address is optional.
-The expression @var{lma} that follows the @code{AT} keyword specifies
-the load address of the section.
-
-Alternatively, with @samp{AT>@var{lma_region}} expression, you may
-specify a memory region for the section's load address. @xref{MEMORY}.
-Note that if the section has not had a VMA assigned to it then the
-linker will use the @var{lma_region} as the VMA region as well.
+The @code{AT} keyword takes an expression as an argument. This
+specifies the exact load address of the section. The @code{AT>} keyword
+takes the name of a memory region as an argument. @xref{MEMORY}. The
+load address of the section is set to the next free address in the
+region, aligned to the section's alignment requirements.
If neither @code{AT} nor @code{AT>} is specified for an allocatable
-section, the linker will set the LMA such that the difference between
-VMA and LMA for the section is the same as the preceding output
-section in the same region. If there is no preceding output section
-or the section is not allocatable, the linker will set the LMA equal
-to the VMA.
-@xref{Output Section Region}.
+section, the linker will use the following heuristic to determine the
+load address:
+
+@itemize @bullet
+@item
+If the section has a specific VMA address, then this is used as
+the LMA address as well.
+
+@item
+If the section is not allocatable then its LMA is set to its VMA.
+
+@item
+Otherwise if a memory region can be found that is compatible
+with the current section, and this region contains at least one
+section, then the LMA is set so the difference between the
+VMA and LMA is the same as the difference between the VMA and LMA of
+the last section in the located region.
+
+@item
+If no memory regions have been declared then a default region
+that covers the entire address space is used in the previous step.
+
+@item
+If no suitable region could be found, or there was no previous
+section then the LMA is set equal to the VMA.
+@end itemize
@cindex ROM initialized data
@cindex initialized data in ROM
char *src = &_etext;
char *dst = &_data;
-/* ROM has data at end of text; copy it. */
-while (dst < &_edata) @{
+/* ROM has data at end of text; copy it. */
+while (dst < &_edata)
*dst++ = *src++;
-@}
-/* Zero bss */
+/* Zero bss. */
for (dst = &_bstart; dst< &_bend; dst++)
*dst = 0;
@end group
@item L
Same as @samp{I}
@item !
-Invert the sense of any of the preceding attributes
+Invert the sense of any of the attributes that follow
@end table
If a unmapped section matches any of the listed attributes other than
of the linker script. It is not put into the output file. Program
header names are stored in a separate name space, and will not conflict
with symbol names, file names, or section names. Each program header
-must have a distinct name.
+must have a distinct name. The headers are processed in order and it
+is usual for them to map to sections in ascending load address order.
Certain program header types describe segments of memory which the
system loader will load from the file. In the linker script, you
@kindex FILEHDR
@kindex PHDRS
-You may use the @code{FILEHDR} and @code{PHDRS} keywords appear after
+You may use the @code{FILEHDR} and @code{PHDRS} keywords after
the program header type to further describe the contents of the segment.
The @code{FILEHDR} keyword means that the segment should include the ELF
file header. The @code{PHDRS} keyword means that the segment should
-include the ELF program headers themselves.
+include the ELF program headers themselves. If applied to a loadable
+segment (@code{PT_LOAD}), all prior loadable segments must have one of
+these keywords.
The @var{type} may be one of the following. The numbers indicate the
value of the keyword.
bar1; bar2;
extern "C++" @{
ns::*;
- "int f(int, double)";
- @}
+ "f(int, double)";
+ @};
@} VERS_1.2;
@end smallexample
The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
The linker will iterate over the list of symbols at the link time and
demangle them according to @samp{lang} before matching them to the
-patterns specified in @samp{version-script-commands}.
+patterns specified in @samp{version-script-commands}. The default
+@samp{lang} is @samp{C}.
Demangled names may contains spaces and other special characters. As
described above, you can use a glob pattern to match demangled names,
@cindex absolute and relocatable symbols
@cindex relocatable and absolute symbols
@cindex symbols, relocatable and absolute
-When the linker evaluates an expression, the result is either absolute
-or relative to some section. A relative expression is expressed as a
-fixed offset from the base of a section.
+Addresses and symbols may be section relative, or absolute. A section
+relative symbol is relocatable. If you request relocatable output
+using the @samp{-r} option, a further link operation may change the
+value of a section relative symbol. On the other hand, an absolute
+symbol will retain the same value throughout any further link
+operations.
+
+Some terms in linker expressions are addresses. This is true of
+section relative symbols and for builtin functions that return an
+address, such as @code{ADDR}, @code{LOADADDR}, @code{ORIGIN} and
+@code{SEGMENT_START}. Other terms are simply numbers, or are builtin
+functions that return a non-address value, such as @code{LENGTH}.
+One complication is that unless you set @code{LD_FEATURE ("SANE_EXPR")}
+(@pxref{Miscellaneous Commands}), numbers and absolute symbols are treated
+differently depending on their location, for compatibility with older
+versions of @code{ld}. Expressions appearing outside an output
+section definition treat all numbers as absolute addresses.
+Expressions appearing inside an output section definition treat
+absolute symbols as numbers. If @code{LD_FEATURE ("SANE_EXPR")} is
+given, then absolute symbols and numbers are simply treated as numbers
+everywhere.
+
+In the following simple example,
-The position of the expression within the linker script determines
-whether it is absolute or relative. An expression which appears within
-an output section definition is relative to the base of the output
-section. An expression which appears elsewhere will be absolute.
+@smallexample
+@group
+SECTIONS
+ @{
+ . = 0x100;
+ __executable_start = 0x100;
+ .data :
+ @{
+ . = 0x10;
+ __data_start = 0x10;
+ *(.data)
+ @}
+ @dots{}
+ @}
+@end group
+@end smallexample
-A symbol set to a relative expression will be relocatable if you request
-relocatable output using the @samp{-r} option. That means that a
-further link operation may change the value of the symbol. The symbol's
-section will be the section of the relative expression.
+both @code{.} and @code{__executable_start} are set to the absolute
+address 0x100 in the first two assignments, then both @code{.} and
+@code{__data_start} are set to 0x10 relative to the @code{.data}
+section in the second two assignments.
-A symbol set to an absolute expression will retain the same value
-through any further link operation. The symbol will be absolute, and
-will not have any particular associated section.
+For expressions involving numbers, relative addresses and absolute
+addresses, ld follows these rules to evaluate terms:
+
+@itemize @bullet
+@item
+Unary operations on a relative address, and binary operations on two
+relative addresses in the same section or between one relative address
+and a number, apply the operator to the offset part of the address(es).
+@item
+Unary operations on an absolute address, and binary operations on one
+or more absolute addresses or on two relative addresses not in the
+same section, first convert any non-absolute term to an absolute
+address before applying the operator.
+@end itemize
+
+The result section of each sub-expression is as follows:
+
+@itemize @bullet
+@item
+An operation involving only numbers results in a number.
+@item
+The result of comparisons, @samp{&&} and @samp{||} is also a number.
+@item
+The result of other operations on relative addresses (after above
+conversions) is a relative address in the same section as the operand(s).
+@item
+The result of other operations on absolute addresses (after above
+conversions) is an absolute address.
+@end itemize
You can use the builtin function @code{ABSOLUTE} to force an expression
to be absolute when it would otherwise be relative. For example, to
If @samp{ABSOLUTE} were not used, @samp{_edata} would be relative to the
@samp{.data} section.
+Using @code{LOADADDR} also forces an expression absolute, since this
+particular builtin function returns an absolute address.
+
@node Builtin Functions
@subsection Builtin Functions
@cindex functions in expressions
@item ADDR(@var{section})
@kindex ADDR(@var{section})
@cindex section address in expression
-Return the absolute address (the VMA) of the named @var{section}. Your
+Return the address (VMA) of the named @var{section}. Your
script must previously have defined the location of that section. In
-the following example, @code{symbol_1} and @code{symbol_2} are assigned
-identical values:
+the following example, @code{start_of_output_1}, @code{symbol_1} and
+@code{symbol_2} are assigned equivalent values, except that
+@code{symbol_1} will be relative to the @code{.output1} section while
+the other two will be absolute:
@smallexample
@group
SECTIONS @{ @dots{}
@item LOADADDR(@var{section})
@kindex LOADADDR(@var{section})
@cindex section load address in expression
-Return the absolute LMA of the named @var{section}. This is normally
-the same as @code{ADDR}, but it may be different if the @code{AT}
-attribute is used in the output section definition (@pxref{Output
+Return the absolute LMA of the named @var{section}. (@pxref{Output
Section LMA}).
@kindex MAX
option) that value will be returned; otherwise the value will be
@var{default}. At present, the @samp{-T} command-line option can only
be used to set the base address for the ``text'', ``data'', and
-``bss'' sections, but you use @code{SEGMENT_START} with any segment
+``bss'' sections, but you can use @code{SEGMENT_START} with any segment
name.
@item SIZEOF(@var{section})
The erratum only affects Thumb-2 code. Please contact ARM for further details.
+@kindex --merge-exidx-entries
+@kindex --no-merge-exidx-entries
+The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo.
+
@ifclear GENERIC
@lowersections
@end ifclear
_bar = bar
another_foo = abc.dll.afoo
var1 DATA
+doo = foo == foo2
+eoo DATA == var1
@end example
-This example defines a DLL with a non-default base address and five
+This example defines a DLL with a non-default base address and seven
symbols in the export table. The third exported symbol @code{_bar} is an
alias for the second. The fourth symbol, @code{another_foo} is resolved
by "forwarding" to another module and treating it as an alias for
@code{afoo} exported from the DLL @samp{abc.dll}. The final symbol
-@code{var1} is declared to be a data object.
+@code{var1} is declared to be a data object. The @samp{doo} symbol in
+export library is an alias of @samp{foo}, which gets the string name
+in export table @samp{foo2}. The @samp{eoo} symbol is an data export
+symbol, which gets in export table the name @samp{var1}.
The optional @code{LIBRARY <name>} command indicates the @emph{internal}
name of the output DLL. If @samp{<name>} does not include a suffix,
EXPORTS
( ( ( <name1> [ = <name2> ] )
| ( <name1> = <module-name> . <external-name>))
- [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] ) *
+ [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) *
@end example
Declares @samp{<name1>} as an exported symbol from the DLL, or declares
@samp{<name1>} as a "forward" alias for the symbol
@samp{<external-name>} in the DLL @samp{<module-name>}.
Optionally, the symbol may be exported by the specified ordinal
-@samp{<integer>} alias.
+@samp{<integer>} alias. The optional @samp{<name3>} is the to be used
+string in import/export table for the symbol.
The optional keywords that follow the declaration indicate:
@cindex Xtensa options
@table @option
-@kindex --no-relax
-@item --no-relax
-Since the Xtensa version of @code{ld} enables the @option{--relax} option
-by default, the @option{--no-relax} option is provided to disable
-relaxation.
-
@item --size-opt
When optimizing indirect calls to direct calls, optimize for code size
more than performance. With this option, the linker will not insert
projects / deliverable / binutils-gdb.git / blobdiff