binutils-gdb/ld
Maciej W. Rozycki 7bd374a44d MIPS/GAS: Implement microMIPS branch/jump compaction
Convert microMIPS branches and jumps whose delay slot would be filled by
a generated NOP instruction to the corresponding compact form where one
exists, in a manner similar to MIPS16 JR->JRC and JALR->JALRC swap.

Do so even where the transformation switches from a 16-bit to a 32-bit
branch encoding for no benefit in code size reduction, as this is still
advantageous.  This is because a branch/NOP pair takes 2 pipeline slots
or a 2-cycle completion latency except in superscalar implementations.
Whereas a compact branch may or may not stall on its target fetch, so it
will at most have a 2-cycle completion latency and may have only 1 even
in scalar implementations, and in superscalar implementations it is
expected to have no worse latency as a branch/NOP pair has.  Also it
won't stall and therefore take the extra latency cycle in the not-taken
case.

Technically this is the same as MIPS16 compaction: for the qualifying
instruction encodings the APPEND_ADD_COMPACT machine code generation
method is selected where APPEND_ADD_WITH_NOP otherwise would and tells
the code generator in `append_insn' to convert the regular form of an
instruction to its corresponding compact form.  For this the opcode is
tweaked as necessary and the microMIPS opcode table is scanned for the
matching updated instruction.  A non-$0 `rt' operand to BEQ and BNE
instructions is moved to the `rs' operand field of BEQZC and BNEZC
encodings as required.

Unlike with MIPS16 compaction however we need to handle out-of-distance
branch relaxation as well.  We do this by deferring the generation of
any delay-slot NOP required to relaxation made in `md_convert_frag', by
converting the APPEND_ADD_WITH_NOP machine code generation to APPEND_ADD
where a relaxed instruction is recorded.  Relaxation then, depending on
actual code produced, chooses between either using a compact branch or
jump encoding and emitting the NOP outstanding if no compact encoding is
possible.

For code simplicity's sake the relaxation pass is retained even if the
principle of preferring a compact encoding to a 16-bit branch/NOP pair
means, in the absence of out-of-range branch relaxation, that a single
compact branch machine code instruction will eventually be produced from
a given assembly source instruction.

	gas/
	* config/tc-mips.c (RELAX_MICROMIPS_ENCODE): Add `nods' flag.
	(RELAX_MICROMIPS_RELAX32, RELAX_MICROMIPS_TOOFAR16)
	(RELAX_MICROMIPS_MARK_TOOFAR16, RELAX_MICROMIPS_CLEAR_TOOFAR16)
	(RELAX_MICROMIPS_TOOFAR32, RELAX_MICROMIPS_MARK_TOOFAR32)
	(RELAX_MICROMIPS_CLEAR_TOOFAR32): Shift bits.
	(get_append_method): Also return APPEND_ADD_COMPACT for
	microMIPS instructions.
	(find_altered_mips16_opcode): Exclude macros from matching.
	Factor code out...
	(find_altered_opcode): ... to this new function.
	(find_altered_micromips_opcode): New function.
	(frag_branch_delay_slot_size): Likewise.
	(append_insn): Handle microMIPS branch/jump compaction.
	(macro_start): Likewise.
	(relaxed_micromips_32bit_branch_length): Likewise.
	(md_convert_frag): Likewise.
	* testsuite/gas/mips/micromips.s: Add conditional explicit NOPs
	for delay slot filling.
	* testsuite/gas/mips/micromips-b16.s: Add explicit NOPs for
	delay slot filling.
	* testsuite/gas/mips/micromips-size-1.s: Likewise.
	* testsuite/gas/mips/micromips.l: Adjust line numbers.
	* testsuite/gas/mips/micromips-warn.l: Likewise.
	* testsuite/gas/mips/micromips-size-1.l: Likewise.
	* testsuite/gas/mips/micromips.d: Adjust padding.
	* testsuite/gas/mips/micromips-trap.d: Likewise.
	* testsuite/gas/mips/micromips-insn32.d: Likewise.
	* testsuite/gas/mips/micromips-noinsn32.d: Likewise.
	* testsuite/gas/mips/micromips@beq.d: Update patterns for
	branch/jump compaction.
	* testsuite/gas/mips/micromips@bge.d: Likewise.
	* testsuite/gas/mips/micromips@bgeu.d: Likewise.
	* testsuite/gas/mips/micromips@blt.d: Likewise.
	* testsuite/gas/mips/micromips@bltu.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-4.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-4-64.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5pic.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5-64.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5pic-64.d: Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local.d: Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local-n32.d:
	Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local-n64.d:
	Likewise.
	* testsuite/gas/mips/micromips@loc-swap.d: Likewise.
	* testsuite/gas/mips/micromips@loc-swap-dis.d: Likewise.
	* testsuite/gas/mips/micromips@relax.d: Likewise.
	* testsuite/gas/mips/micromips@relax-at.d: Likewise.
	* testsuite/gas/mips/micromips@relax-swap3.d: Likewise.
	* testsuite/gas/mips/branch-extern-2.d: Likewise.
	* testsuite/gas/mips/branch-extern-4.d: Likewise.
	* testsuite/gas/mips/branch-section-2.d: Likewise.
	* testsuite/gas/mips/branch-section-4.d: Likewise.
	* testsuite/gas/mips/branch-weak-2.d: Likewise.
	* testsuite/gas/mips/branch-weak-5.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-n32.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-n64.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend.d:
	Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend-n32.d:
	Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend-n64.d:
	Likewise.
	* testsuite/gas/mips/micromips-compact.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new test.

	ld/
	* testsuite/ld-mips-elf/micromips-branch-absolute.d: Update
	patterns for branch compaction.
	* testsuite/ld-mips-elf/micromips-branch-absolute-addend.d:
	Likewise.

	opcodes/
	* micromips-opc.c (micromips_opcodes): Reorder "bc" next to "b",
	"beqzc" next to "beq", "bnezc" next to "bne" and "jrc" next to
	"j".
2016-07-27 17:38:31 +01:00
..
emulparams Support -pie for aarch64*-elf targets. 2016-07-19 10:19:06 -07:00
emultempl Don't include libbfd.h outside of bfd, part 1 2016-07-16 13:25:11 +09:30
po Copyright update for binutils 2016-01-01 23:00:01 +10:30
scripttempl FT32 linker script cleanup 2016-07-06 18:58:10 -07:00
testsuite MIPS/GAS: Implement microMIPS branch/jump compaction 2016-07-27 17:38:31 +01:00
.gitignore
ChangeLog MIPS/GAS: Implement microMIPS branch/jump compaction 2016-07-27 17:38:31 +01:00
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MAINTAINERS Copyright update for binutils 2016-01-01 23:00:01 +10:30
Makefile.am Don't include libbfd.h outside of bfd, part 1 2016-07-16 13:25:11 +09:30
Makefile.in Don't include libbfd.h outside of bfd, part 1 2016-07-16 13:25:11 +09:30
NEWS Add support for creating ELF import libraries 2016-07-15 17:50:48 +01:00
README Copyright update for binutils 2016-01-01 23:00:01 +10:30
TODO
aclocal.m4 Regenerate Makefile.in/aclocal.m4 automake 1.11.6 2016-04-15 16:20:55 -07:00
config.in ld: Add a linker configure option --enable-relro 2016-06-22 05:37:38 -07:00
configure Set BFD_VERSION to 2.27.51 2016-07-21 15:22:13 -07:00
configure.ac ld: Add a linker configure option --enable-relro 2016-06-22 05:37:38 -07:00
configure.host Copyright update for binutils 2016-01-01 23:00:01 +10:30
configure.tgt ld: Add a linker configure option --enable-relro 2016-06-22 05:37:38 -07:00
deffile.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
deffilep.y Copyright update for binutils 2016-01-01 23:00:01 +10:30
dep-in.sed
elf-hints-local.h
fdl.texi
gen-doc.texi Copyright update for binutils 2016-01-01 23:00:01 +10:30
genscrba.sh
genscripts.sh Copyright update for binutils 2016-01-01 23:00:01 +10:30
h8-doc.texi Copyright update for binutils 2016-01-01 23:00:01 +10:30
ld.h Add support for creating ELF import libraries 2016-07-15 17:50:48 +01:00
ld.texinfo Add support for creating ELF import libraries 2016-07-15 17:50:48 +01:00
ldbuildid.c Fix warning in ldbuildid.c mingw32 code 2016-07-27 19:03:22 +09:30
ldbuildid.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldcref.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldctor.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldctor.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldemul.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldemul.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldexp.c Early expression evaluation 2016-07-20 10:55:45 +09:30
ldexp.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldfile.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldfile.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldgram.y Add new NOCROSSREFS_TO linker script command 2016-04-18 12:45:46 +01:00
ldint.texinfo Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldlang.c Don't include libbfd.h outside of bfd, part 4 2016-07-16 13:29:35 +09:30
ldlang.h Add new NOCROSSREFS_TO linker script command 2016-04-18 12:45:46 +01:00
ldlex-wrapper.c Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldlex.h Add support for creating ELF import libraries 2016-07-15 17:50:48 +01:00
ldlex.l ld: track linker-definedness of symbols 2016-07-05 11:36:08 +02:00
ldmain.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldmain.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldmisc.c Delete bfd_my_archive macro 2016-06-14 13:24:37 +09:30
ldmisc.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldver.c Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldver.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
ldwrite.c Formatting fixes. 2016-06-14 13:25:21 +09:30
ldwrite.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
lexsup.c Add support for creating ELF import libraries 2016-07-15 17:50:48 +01:00
mri.c Copyright update for binutils 2016-01-01 23:00:01 +10:30
mri.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
pe-dll.c Ignore DWARF debug information with a version of 0 - assume that it is padding. 2016-04-04 12:53:33 +01:00
pe-dll.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
pep-dll.c Copyright update for binutils 2016-01-01 23:00:01 +10:30
pep-dll.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
plugin.c ld: Restore file offset after a plugin fails to claim a file 2016-07-19 09:58:01 +01:00
plugin.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
stamp-h.in
sysdep.h Copyright update for binutils 2016-01-01 23:00:01 +10:30
testplug.c ld: Restore file offset after a plugin fails to claim a file 2016-07-19 09:58:01 +01:00
testplug2.c Remove redundant sizeof on EXPECTED_VIEW_LENGTH 2016-05-14 05:51:28 -07:00
testplug3.c Copyright update for binutils 2016-01-01 23:00:01 +10:30
testplug4.c Remove redundant sizeof on EXPECTED_VIEW_LENGTH 2016-05-14 05:51:28 -07:00

README

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		README for LD

This is the GNU linker.  It is distributed with other "binary
utilities" which should be in ../binutils.  See ../binutils/README for
more general notes, including where to send bug reports.

There are many features of the linker:

* The linker uses a Binary File Descriptor library (../bfd)
  that it uses to read and write object files.  This helps
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* The linker supports a number of different object file
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Installation
============

See ../binutils/README.

If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.

To build just the linker, make the target all-ld from the top level
directory (one directory above this one).

Porting to a new target
=======================

See the ldint.texinfo manual.

Reporting bugs etc
===========================

See ../binutils/README.

Known problems
==============

The Solaris linker normally exports all dynamic symbols from an
executable.  The GNU linker does not do this by default.  This is
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HP/UX 9.01 has a shell bug that causes the linker scripts to be
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  * Build and install bash, and build with "make SHELL=bash".
  * Update to a version of HP/UX with a working shell (e.g., 9.05).
  * Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
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