PORTING:
-Sorry, no description of the interfaces is written up yet. Look at
-existing back ends and work from there.
+Sorry, no description of the interfaces is written up yet. Look at existing
+back ends and work from there.
-New hosts: If your host system has a strange header file setup, create
-a config/ho-foo.h file for it and include the appropriate header files
-or definitions there. If your host has a broken compiler, or some
-broken macros in header files, create a host-specific file and repair
-the damage there. (See, for example, ho-rs6000.h. The "assert" macro
-on that system doesn't work right, and a flag is set to rewrite an
-expression in tc-m68k.c that the native compiler mis-compiles.)
+New hosts: If your host system has a strange header file setup, create a
+config/ho-foo.h file for it and include the appropriate header files or
+definitions there. If your host has a broken compiler, or some broken macros
+in header files, create a host-specific file and repair the damage there.
+(See, for example, ho-rs6000.h. The "assert" macro on that system doesn't work
+right, and a flag is set to rewrite an expression in tc-m68k.c that the native
+compiler mis-compiles.)
-New target formats: Look at the BFD_ASSEMBLER code. The a.out code
-might be a fair example. There are no "good" examples yet,
-unfortunately.
+New target formats: Look at the BFD_ASSEMBLER code. The a.out code might be a
+fair example. There are no "good" examples yet, unfortunately, nor any good
+documentation of the changes.
-New target processors: Check first to see if the BFD_ASSEMBLER
-interface is supported by the file format code you need to use.
+New target processors: Check first to see if the BFD_ASSEMBLER interface is
+supported by the file format code you need to use.
New environments: ???
The internals of gas need documenting.
-Roland's going to work on removing the m4 processing from the user
-documentation. With the latest texinfo code, it's not needed.
+The documentation should also contain a "Trouble" section similar to gcc's
+manual: real bugs, common problems, incompatibilities, etc.
Anyone want to offer to maintain a man page?
BFD CONVERSION:
-The "#ifdef BFD_ASSEMBLER" code is on its way in; the "#ifndef
-BFD_ASSEMBLER" code is on its way out. The new code uses BFD data
-structures, and calls BFD for anything that needs to be written to the
-output file. The old code did all the writing itself, or in a couple
-of cases, used BFD as a slightly higher level than stdio (i.e.,
-bfd_seek, bfd_write -- these are not the preferred interface).
+The "#ifdef BFD_ASSEMBLER" code is on its way in; the "#ifndef BFD_ASSEMBLER"
+code is on its way out. The new code uses BFD data structures, and calls BFD
+for anything that needs to be written to the output file. The old code did all
+the writing itself, or in a couple of cases, used BFD as a slightly higher
+level than stdio (i.e., bfd_seek, bfd_write -- these are not the preferred
+interface).
Because of this, some of this code is messy. Lots of ifdef's, and the
-non-BFD_ASSEMBLER version often has multiple conditional tests inside
-it for various processors or formats. As the various targets get
-converted over, these will gradually go away.
+non-BFD_ASSEMBLER version often has multiple conditional tests inside it for
+various processors or formats. As the various targets get converted over,
+these will gradually go away.
-As of the moment I'm editing this file, only the "sun4" target can
-really use the BFD code. Other back ends still need merging or
+As of the moment I'm editing this file, only the "sun4" and "decstation-bsd"
+targets can really use the BFD code. Other back ends still need merging or
touching up.
TO DO:
Remove DONTDEF code, commented-out code.
-Eliminate, as much as possible, anything not in config that is
-conditionalized on a CPU, format, or environment.
+Eliminate, as much as possible, anything not in config that is conditionalized
+on a CPU, format, or environment.
-Finish conversion to using BFD for all object file writing. (This is
-the BFD_ASSEMBLER code, not BFD or BFD_HEADERS.) VMS might be the
-tough one here, since there's no BFD support for it at all yet.
-Eliminate the old code.
+Merge COFF support into one version, supporting all the pseudo-ops used in
+either versions now, but using BFD for high-level operations. (See second
+following item.) Currently there are two versions (plus the new BFD code),
+which support different features, and are used on different targets.
-Clean up comments; lots of 'em are one previous maintainer griping
-about another previous maintainer, unrelated to the code. (And with
-no names, they're not so fun to read. :-)
+Convert remaining a.out/b.out targets to using the BFD_ASSEMBLER code by
+default.
-Get Steve to document H8/500 stuff.
+Finish conversion to using BFD for all object file writing. (This is the
+BFD_ASSEMBLER code, not BFD or BFD_HEADERS.) VMS might be the tough one here,
+since there's no BFD support for it at all yet. Eliminate the old code. Some
+of this can be done target by target, so doing a target where the CPU or
+format already supports BFD_ASSEMBLER mode may be easiest.
+
+Fix lots of uses of empty strings to use null pointers. Will improve
+efficiency, and should make code clearer too.
+
+Clean up comments; lots of 'em are one previous maintainer griping about
+another previous maintainer, unrelated to the code. (And with no names,
+they're not so fun to read. :-)
+
+For sparc: "call 0" becomes "jmpl %g0,%l7", and similarly for absolute
+addresses in -4096...4095. (Solaris assembler does this. No
+relocation required, no absolute symbol needed.) For addresses
+outside the range, for COFF, keep generating an absolute symbol to use
+for relocs.
+
+Get Steve to document H8/500 stuff (and others).
+
+Improve test suite. Incorporate more reported net bugs, and non-confidential
+Cygnus customer bugs, and anything else.
+
+Add support for i386/i486 16-bit mode, so operating system initialization code
+doesn't require a separate assembler nor lots of `.byte' directives.
+
+See if it's more maintainable (and not too much of a performance loss) to use
+a yacc grammar for parsing input. The lexer will have to be flexible, and the
+grammar will have to contain any construct used on any platform, but it may be
+easier to maintain, instead of having code in most of the back ends.
+
+PIC support.
+
+Torbjorn Granlund <tege@cygnus.com> writes, regarding alpha .align:
+
+ Please make sure the .align directive works as in digital's assembler.
+ They fill the space with a sequence of "bis $31,$31,$31;ldq_u $31,0($30)"
+ since these two instructions can dual-issue. Since .align is ued a lot by
+ gcc, it is an important optimization.
+
+Torbjorn Granlund <tege@cygnus.com> writes, regarding i386/i486/pentium:
+
+ In a new publication from Intel, "Optimization for Intel's 32 bit
+ Processors", they recommended code alignment on a 16 byte boundary if that
+ requires less than 8 bytes of fill instructions. The Pentium is not
+ affected by such alignment, the 386 wants alignment on a 4 byte boundary.
+ It is the 486 that is most helped by large alignment.
+
+ Recommended nop instructions:
+ 1 byte: 90 xchg %eax,%eax
+ 2 bytes: 8b c0 movl %eax,%eax
+ 3 bytes: 8d 76 00 leal 0(%esi),%esi
+ 4 bytes: 8d 74 26 00 leal 0(%esi),%esi
+ 5 bytes: 8b c0 8d 76 00 movl %eax,%eax; leal 0(%esi),%esi
+ 6 bytes: 8d b6 00 00 00 00 leal 0(%esi),%esi
+ 7 bytes: 8d b4 26 00 00 00 00 leal 0(%esi),%esi
+
+ Note that `leal 0(%esi),%esi' has a few different encodings...
+
+ There are faster instructions for certain lengths, that are not true nops.
+ If you can determine that a register and the condition code is dead (by
+ scanning forwards for a register that is written before it is read, and
+ similar for cc) you can use a `incl reg' for a 3 times faster 1 cycle nop...
(From old "NOTES" file to-do list, not really reviewed:)
projects / deliverable / binutils-gdb.git / blobdiff