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relax jalr $t9 [R_MIPS_JALR symbol] to bal symbol
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: binutils at sources dot redhat dot com
- Date: 24 Mar 2003 02:02:00 -0300
- Subject: relax jalr $t9 [R_MIPS_JALR symbol] to bal symbol
- Organization: GCC Team, Red Hat
The idea of the optimization is to take advantage of the R_MIPS_JALR
relocations emitted by the n32 and n64 assemblers to avoid pipeline
stalls due to dependencies between the instruction that loads the
symbol address into $t9 and the jalr instruction, that, because of the
way GCC generates code, will generally be adjacent. If symbol is
reachable with a branch, and it's not overridable, we replace the jump
with a branch. The transformation is only enabled when the --relax
flag is passed to the linker. Tested on mips64-linux-gnu. Ok to
install?
Index: bfd/ChangeLog
from Alexandre Oliva <aoliva at redhat dot com>
* elfxx-mips.c (_bfd_mips_relax_section): New function.
* elfxx-mips.h (_bfd_mips_relax_section): Declare.
* elfn32-mips.c, elf64-mips.c: Use it.
Index: bfd/elf64-mips.c
===================================================================
RCS file: /cvs/uberbaum/bfd/elf64-mips.c,v
retrieving revision 1.46
diff -u -p -r1.46 elf64-mips.c
--- bfd/elf64-mips.c 12 Mar 2003 23:05:51 -0000 1.46
+++ bfd/elf64-mips.c 24 Mar 2003 04:55:38 -0000
@@ -2887,6 +2887,7 @@ const struct elf_size_info mips_elf64_si
#define bfd_elf64_canonicalize_reloc mips_elf64_canonicalize_reloc
#define bfd_elf64_get_dynamic_reloc_upper_bound mips_elf64_get_dynamic_reloc_upper_bound
#define bfd_elf64_canonicalize_dynamic_reloc mips_elf64_canonicalize_dynamic_reloc
+#define bfd_elf64_bfd_relax_section _bfd_mips_relax_section
/* MIPS ELF64 archive functions. */
#define bfd_elf64_archive_functions
Index: bfd/elfn32-mips.c
===================================================================
RCS file: /cvs/uberbaum/bfd/elfn32-mips.c,v
retrieving revision 1.8
diff -u -p -r1.8 elfn32-mips.c
--- bfd/elfn32-mips.c 12 Mar 2003 23:05:51 -0000 1.8
+++ bfd/elfn32-mips.c 24 Mar 2003 04:55:39 -0000
@@ -2211,6 +2211,7 @@ static const struct ecoff_debug_swap mip
#define bfd_elf32_bfd_set_private_flags _bfd_mips_elf_set_private_flags
#define bfd_elf32_bfd_print_private_bfd_data \
_bfd_mips_elf_print_private_bfd_data
+#define bfd_elf32_bfd_relax_section _bfd_mips_relax_section
/* Support for SGI-ish mips targets using n32 ABI. */
Index: bfd/elfxx-mips.c
===================================================================
RCS file: /cvs/uberbaum/bfd/elfxx-mips.c,v
retrieving revision 1.46
diff -u -p -r1.46 elfxx-mips.c
--- bfd/elfxx-mips.c 12 Mar 2003 23:05:51 -0000 1.46
+++ bfd/elfxx-mips.c 24 Mar 2003 04:55:44 -0000
@@ -5451,6 +5451,197 @@ _bfd_mips_elf_check_relocs (abfd, info,
return TRUE;
}
+bfd_boolean
+_bfd_mips_relax_section (abfd, sec, link_info, again)
+ bfd *abfd;
+ asection *sec;
+ struct bfd_link_info *link_info;
+ bfd_boolean *again;
+{
+ Elf_Internal_Rela *internal_relocs;
+ Elf_Internal_Rela *irel, *irelend;
+ Elf_Internal_Shdr *symtab_hdr;
+ bfd_byte *contents = NULL;
+ bfd_byte *free_contents = NULL;
+ size_t extsymoff;
+ bfd_boolean changed_contents = FALSE;
+ bfd_vma sec_start = sec->output_section->vma + sec->output_offset;
+ Elf_Internal_Sym *isymbuf = NULL;
+ unsigned long instruction = 0;
+
+ /* We are not currently changing any sizes, so only one pass. */
+ *again = FALSE;
+
+ if (link_info->relocateable)
+ return TRUE;
+
+ internal_relocs = (MNAME(abfd,_bfd_elf,link_read_relocs)
+ (abfd, sec, (PTR) NULL, (Elf_Internal_Rela *) NULL,
+ link_info->keep_memory));
+ if (internal_relocs == NULL)
+ return TRUE;
+
+ irelend = internal_relocs + sec->reloc_count
+ * get_elf_backend_data (abfd)->s->int_rels_per_ext_rel;
+ symtab_hdr = &elf_tdata (abfd)->symtab_hdr;
+ extsymoff = (elf_bad_symtab (abfd)) ? 0 : symtab_hdr->sh_info;
+
+ for (irel = internal_relocs; irel < irelend; irel++)
+ {
+ bfd_vma symval;
+ bfd_signed_vma sym_offset;
+ unsigned int r_type;
+ unsigned long r_symndx;
+ asection *sym_sec;
+
+ /* Turn jalr into bgezal, and jr into beq, if they're marked
+ with a JALR relocation, that indicate where they jump to.
+ This saves some pipeline bubbles. */
+ r_type = ELF_R_TYPE (abfd, irel->r_info);
+ if (r_type != R_MIPS_JALR)
+ continue;
+
+ if (contents)
+ {
+ instruction = bfd_get_32 (abfd, contents + irel->r_offset);
+ /* if it's neither jalr nor jr, bail out. */
+ if ((instruction & 0xfc1fffff) != 0x0000f809
+ && (instruction & 0xfc1fffff) != 0x00000008)
+ continue;
+ }
+
+ r_symndx = ELF_R_SYM (abfd, irel->r_info);
+ /* Compute the address of the jump target. */
+ if (r_symndx >= extsymoff)
+ {
+ struct mips_elf_link_hash_entry *h
+ = ((struct mips_elf_link_hash_entry *)
+ elf_sym_hashes (abfd) [r_symndx - extsymoff]);
+
+ while (h->root.root.type == bfd_link_hash_indirect
+ || h->root.root.type == bfd_link_hash_warning)
+ h = (struct mips_elf_link_hash_entry *) h->root.root.u.i.link;
+
+ /* If a symbol is undefined, or if it may be overridden,
+ skip it. */
+ if (! ((h->root.root.type == bfd_link_hash_defined
+ || h->root.root.type == bfd_link_hash_defweak)
+ && h->root.root.u.def.section)
+ || (link_info->shared && ! link_info->symbolic
+ && ! (h->root.elf_link_hash_flags & ELF_LINK_FORCED_LOCAL)))
+ continue;
+
+ sym_sec = h->root.root.u.def.section;
+ if (sym_sec->output_section)
+ symval = (h->root.root.u.def.value
+ + sym_sec->output_section->vma
+ + sym_sec->output_offset);
+ else
+ symval = h->root.root.u.def.value;
+ }
+ else
+ {
+ Elf_Internal_Sym *isym;
+
+ /* Read this BFD's symbols if we haven't done so already. */
+ if (isymbuf == NULL && symtab_hdr->sh_info != 0)
+ {
+ isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
+ if (isymbuf == NULL)
+ isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
+ symtab_hdr->sh_info, 0,
+ NULL, NULL, NULL);
+ if (isymbuf == NULL)
+ goto relax_return;
+ }
+
+ isym = isymbuf + r_symndx;
+ if (isym->st_shndx == SHN_UNDEF)
+ continue;
+ else if (isym->st_shndx == SHN_ABS)
+ sym_sec = bfd_abs_section_ptr;
+ else if (isym->st_shndx == SHN_COMMON)
+ sym_sec = bfd_com_section_ptr;
+ else
+ sym_sec
+ = bfd_section_from_elf_index (abfd, isym->st_shndx);
+ symval = isym->st_value
+ + sym_sec->output_section->vma
+ + sym_sec->output_offset;
+ }
+
+ /* Compute branch offset, from delay slot of the jump to the
+ branch target. */
+ sym_offset = (symval + irel->r_addend)
+ - (sec_start + irel->r_offset + 4);
+
+ /* Branch offset must be properly aligned. */
+ if ((sym_offset & 3) != 0)
+ continue;
+
+ sym_offset >>= 2;
+
+ /* Check that it's in range. */
+ if (sym_offset < -0x8000 || sym_offset >= 0x8000)
+ continue;
+
+ /* Get the section contents if we haven't done so already. */
+ if (contents == NULL)
+ {
+ /* Get cached copy if it exists. */
+ if (elf_section_data (sec)->this_hdr.contents != NULL)
+ contents = elf_section_data (sec)->this_hdr.contents;
+ else
+ {
+ contents = (bfd_byte *) bfd_malloc (sec->_raw_size);
+ if (contents == NULL)
+ goto relax_return;
+
+ free_contents = contents;
+ if (! bfd_get_section_contents (abfd, sec, contents,
+ (file_ptr) 0, sec->_raw_size))
+ goto relax_return;
+ }
+
+ /* Since we didn't have contents before, we hadn't checked
+ whether we had the right instruction, so do it now. */
+ instruction = bfd_get_32 (abfd, contents + irel->r_offset);
+ /* if it's neither jalr nor jr, bail out. */
+ if ((instruction & 0xfc1fffff) != 0x0000f809
+ && (instruction & 0xfc1fffff) != 0x00000008)
+ continue;
+ }
+
+ /* If it was jalr <reg>, turn it into bgezal $0, <target>. */
+ if ((instruction & 0xfc1fffff) != 0x0000f809)
+ instruction = 0x10000000;
+ else if ((instruction & 0xfc1fffff) != 0x00000008)
+ instruction = 0x04110000;
+
+ instruction |= (sym_offset & 0xffff);
+ bfd_put_32 (abfd, instruction, contents + irel->r_offset);
+ changed_contents = TRUE;
+ }
+
+ if (contents != NULL
+ && elf_section_data (sec)->this_hdr.contents != contents)
+ {
+ if (!changed_contents && !link_info->keep_memory)
+ free (contents);
+ else
+ {
+ /* Cache the section contents for elf_link_input_bfd. */
+ elf_section_data (sec)->this_hdr.contents = contents;
+ }
+ }
+ return TRUE;
+
+ relax_return:
+ if (free_contents != NULL)
+ free (free_contents);
+ return FALSE;
+}
+
/* Adjust a symbol defined by a dynamic object and referenced by a
regular object. The current definition is in some section of the
dynamic object, but we're not including those sections. We have to
Index: bfd/elfxx-mips.h
===================================================================
RCS file: /cvs/uberbaum/bfd/elfxx-mips.h,v
retrieving revision 1.8
diff -u -p -r1.8 elfxx-mips.h
--- bfd/elfxx-mips.h 23 Jan 2003 11:51:33 -0000 1.8
+++ bfd/elfxx-mips.h 24 Mar 2003 04:55:44 -0000
@@ -108,3 +108,6 @@ extern bfd_reloc_status_type _bfd_mips_e
PARAMS ((bfd *, arelent *, asymbol *, PTR, asection *, bfd *, char **));
extern unsigned long _bfd_elf_mips_mach
PARAMS ((flagword));
+extern bfd_boolean _bfd_mips_relax_section (bfd *, asection *,
+ struct bfd_link_info *,
+ bfd_boolean *);
Index: ld/testsuite/ChangeLog
from Alexandre Oliva <aoliva at redhat dot com>
* ld-mips-elf/mips-elf.exp: Added...
* ld-mips-elf/relax-jalr.s, ld-mips-elf/relax-jalr-n32.d,
ld-mips-elf/relax-jalr-n32-shared.d, ld-mips-elf/relax-jalr-n64.d,
ld-mips-elf/relax-jalr-n64-shared.d: New tests.
Index: ld/testsuite/ld-mips-elf/mips-elf.exp
===================================================================
RCS file: /cvs/uberbaum/ld/testsuite/ld-mips-elf/mips-elf.exp,v
retrieving revision 1.9
diff -u -p -r1.9 mips-elf.exp
--- ld/testsuite/ld-mips-elf/mips-elf.exp 11 Mar 2003 19:20:16 -0000 1.9
+++ ld/testsuite/ld-mips-elf/mips-elf.exp 24 Mar 2003 04:55:46 -0000
@@ -33,6 +33,11 @@ if { [istarget mips*-*-*] } then {
# Test multi-got link.
run_dump_test "multi-got-1"
+
+ run_dump_test "relax-jalr-n32"
+ run_dump_test "relax-jalr-n32-shared"
+ run_dump_test "relax-jalr-n64"
+ run_dump_test "relax-jalr-n64-shared"
}
if { $linux_gnu } {
Index: ld/testsuite/ld-mips-elf/relax-jalr-n32-shared.d
===================================================================
RCS file: ld/testsuite/ld-mips-elf/relax-jalr-n32-shared.d
diff -N ld/testsuite/ld-mips-elf/relax-jalr-n32-shared.d
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-mips-elf/relax-jalr-n32-shared.d 24 Mar 2003 04:55:46 -0000
@@ -0,0 +1,23 @@
+#name: MIPS relax-jalr-shared n32
+#source: relax-jalr.s
+#as: -KPIC -n32
+#objdump: --prefix-addresses -d --show-raw-insn
+#ld: --relax -shared -melf32btsmipn32
+
+.*: file format elf.*mips.*
+
+Disassembly of section \.text:
+ \.\.\.
+ \.\.\.
+.* lw t9,.*
+.* jalr t9
+.* nop
+ \.\.\.
+.* lw t9,.*
+.* jalr t9
+.* nop
+ \.\.\.
+.* lw t9,.*
+.* bal .* <__start>
+.* nop
+ \.\.\.
Index: ld/testsuite/ld-mips-elf/relax-jalr-n32.d
===================================================================
RCS file: ld/testsuite/ld-mips-elf/relax-jalr-n32.d
diff -N ld/testsuite/ld-mips-elf/relax-jalr-n32.d
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-mips-elf/relax-jalr-n32.d 24 Mar 2003 04:55:46 -0000
@@ -0,0 +1,23 @@
+#name: MIPS relax-jalr n32
+#source: relax-jalr.s
+#as: -KPIC -n32
+#objdump: --prefix-addresses -d --show-raw-insn
+#ld: --relax -melf32btsmipn32
+
+.*: file format elf.*mips.*
+
+Disassembly of section \.text:
+ \.\.\.
+ \.\.\.
+.* lw t9,.*
+.* bal .* <__start>
+.* nop
+ \.\.\.
+.* lw t9,.*
+.* bal .* <__start>
+.* nop
+ \.\.\.
+.* lw t9,.*
+.* bal .* <__start>
+.* nop
+.* nop
Index: ld/testsuite/ld-mips-elf/relax-jalr-n64-shared.d
===================================================================
RCS file: ld/testsuite/ld-mips-elf/relax-jalr-n64-shared.d
diff -N ld/testsuite/ld-mips-elf/relax-jalr-n64-shared.d
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-mips-elf/relax-jalr-n64-shared.d 24 Mar 2003 04:55:46 -0000
@@ -0,0 +1,25 @@
+#name: MIPS relax-jalr-shared n64
+#source: relax-jalr.s
+#as: -KPIC -64
+#objdump: --prefix-addresses -d --show-raw-insn
+#ld: --relax -shared -melf64btsmip
+
+.*: file format elf.*mips.*
+
+Disassembly of section \.text:
+ \.\.\.
+ \.\.\.
+.* ld t9,.*
+.* jalr t9
+.* nop
+ \.\.\.
+.* ld t9,.*
+.* jalr t9
+.* nop
+ \.\.\.
+.* ld t9,.*
+.* bal .* <__start>
+.* nop
+.* nop
+Disassembly of section \.MIPS\.stubs:
+ \.\.\.
Index: ld/testsuite/ld-mips-elf/relax-jalr-n64.d
===================================================================
RCS file: ld/testsuite/ld-mips-elf/relax-jalr-n64.d
diff -N ld/testsuite/ld-mips-elf/relax-jalr-n64.d
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-mips-elf/relax-jalr-n64.d 24 Mar 2003 04:55:46 -0000
@@ -0,0 +1,23 @@
+#name: MIPS relax-jalr n64
+#source: relax-jalr.s
+#as: -KPIC -64
+#objdump: --prefix-addresses -d --show-raw-insn
+#ld: --relax -melf64btsmip
+
+.*: file format elf.*mips.*
+
+Disassembly of section \.text:
+ \.\.\.
+ \.\.\.
+.* ld t9,.*
+.* bal .* <__start>
+.* nop
+ \.\.\.
+.* ld t9,.*
+.* bal .* <__start>
+.* nop
+ \.\.\.
+.* ld t9,.*
+.* bal .* <__start>
+.* nop
+.* nop
Index: ld/testsuite/ld-mips-elf/relax-jalr.s
===================================================================
RCS file: ld/testsuite/ld-mips-elf/relax-jalr.s
diff -N ld/testsuite/ld-mips-elf/relax-jalr.s
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-mips-elf/relax-jalr.s 24 Mar 2003 04:55:46 -0000
@@ -0,0 +1,12 @@
+.globl __start
+ .space 8
+.ent __start
+__start:
+.Lstart:
+ .space 16
+ jal __start
+ .space 32
+ jal __start
+ .space 64
+ jal .Lstart
+.end __start
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva at {redhat dot com, gcc.gnu.org}
CS PhD student at IC-Unicamp oliva at {lsd dot ic dot unicamp dot br, gnu.org}
Free Software Evangelist Professional serial bug killer