2
0
mirror of https://sourceware.org/git/binutils-gdb.git synced 2024-12-21 04:42:53 +08:00
binutils-gdb/gas/subsegs.c
H.J. Lu d1bcae833b ELF: Don't generate unused section symbols
For ELF targets, section symbols are required only for relocations.
With -ffunction-sections -fdata-sections, there can be many unused
section symbols.  Sizes of libstdc++.a on Linux/x86-64 in GCC 11 are

With unused section symbols   : 39411698 bytes
Without unused section symbols: 39227002 bytes

The unused section symbols in libstdc++.a occupy more than 180 KB.

Add BSF_SECTION_SYM_USED to indicate if a section symbol should be
included in the symbol table.  The BSF_SECTION_SYM_USED should be set
if the section symbol is used for relocation or the section symbol is
always included in the symbol table.

Add keep_unused_section_symbols to bfd_target to indicate if unused
section symbols should be kept.  If TARGET_KEEP_UNUSED_SECTION_SYMBOLS
is defined as FALSE, unused ection symbols will be removed.

Tested on Linux/x86.  Other ELF backends need to:

1. Define TARGET_KEEP_UNUSED_SECTION_SYMBOLS to FALSE.
2. Mark used section symbols in assembler backend.
3. Remove unused section symbols from expected assembler and linker
outputs.

bfd/

	PR 27109
	* aix386-core.c (core_aix386_vec): Initialize
	keep_unused_section_symbol to TARGET_KEEP_UNUSED_SECTION_SYMBOLS.
	* aout-target.h (MY (vec)): Likewise.
	* binary.c (binary_vec): Likewise.
	* cisco-core.c (core_cisco_be_vec): Likewise.
	(core_cisco_le_vec): Likewise.
	* coff-alpha.c (alpha_ecoff_le_vec): Likewise.
	* coff-i386.c (TARGET_SYM): Likewise.
	(TARGET_SYM_BIG): Likewise.
	* coff-ia64.c (TARGET_SYM): Likewise.
	* coff-mips.c (mips_ecoff_le_vec): Likewise.
	(mips_ecoff_be_vec): Likewise.
	(mips_ecoff_bele_vec): Likewise.
	* coff-rs6000.c (rs6000_xcoff_vec): Likewise.
	(powerpc_xcoff_vec): Likewise.
	* coff-sh.c (sh_coff_small_vec): Likewise.
	(sh_coff_small_le_vec): Likewise.
	* coff-tic30.c (tic30_coff_vec): Likewise.
	* coff-tic54x.c (tic54x_coff0_vec): Likewise.
	(tic54x_coff0_beh_vec): Likewise.
	(tic54x_coff1_vec): Likewise.
	(tic54x_coff1_beh_vec): Likewise.
	(tic54x_coff2_vec): Likewise.
	(tic54x_coff2_beh_vec): Likewise.
	* coff-x86_64.c (TARGET_SYM): Likewise.
	(TARGET_SYM_BIG): Likewise.
	* coff64-rs6000.c (rs6000_xcoff64_vec): Likewise.
	(rs6000_xcoff64_aix_vec): Likewise.
	* coffcode.h (CREATE_BIG_COFF_TARGET_VEC): Likewise.
	(CREATE_BIGHDR_COFF_TARGET_VEC): Likewise.
	(CREATE_LITTLE_COFF_TARGET_VEC): Likewise.
	* elfxx-target.h (TARGET_BIG_SYM): Likewise.
	(TARGET_LITTLE_SYM): Likewise.
	* hppabsd-core.c (core_hppabsd_vec): Likewise.
	* hpux-core.c (core_hpux_vec): Likewise.
	* i386msdos.c (i386_msdos_vec): Likewise.
	* ihex.c (ihex_vec): Likewise.
	* irix-core.c (core_irix_vec): Likewise.
	* mach-o-target.c (TARGET_NAME): Likewise.
	* mmo.c (mmix_mmo_vec): Likewise.
	* netbsd-core.c (core_netbsd_vec): Likewise.
	* osf-core.c (core_osf_vec): Likewise.
	* pdp11.c (MY (vec)): Likewise.
	* pef.c (pef_vec): Likewise.
	(pef_xlib_vec): Likewise.
	* plugin.c (plugin_vec): Likewise.
	* ppcboot.c (powerpc_boot_vec): Likewise.
	* ptrace-core.c (core_ptrace_vec): Likewise.
	* sco5-core.c (core_sco5_vec): Likewise.
	* som.c (hppa_som_vec): Likewise.
	* srec.c (srec_vec): Likewise.
	(symbolsrec_vec): Likewise.
	* tekhex.c (tekhex_vec): Likewise.
	* trad-core.c (core_trad_vec): Likewise.
	* verilog.c (verilog_vec): Likewise.
	* vms-alpha.c (alpha_vms_vec): Likewise.
	* vms-lib.c (alpha_vms_lib_txt_vec): Likewise.
	* wasm-module.c (wasm_vec): Likewise.
	* xsym.c (sym_vec): Likewise.
	* elf.c (ignore_section_sym): Return TRUE if BSF_SECTION_SYM_USED
	isn't set.
	(elf_map_symbols): Don't include ignored section symbols.
	* elfcode.h (elf_slurp_symbol_table): Also set
	BSF_SECTION_SYM_USED on STT_SECTION symbols.
	* elflink.c (bfd_elf_final_link): Generated section symbols only
	when emitting relocations or reqired.
	* elfxx-x86.h (TARGET_KEEP_UNUSED_SECTION_SYMBOLS): New.
	* syms.c (BSF_SECTION_SYM_USED): New.
	* targets.c (TARGET_KEEP_UNUSED_SECTION_SYMBOLS): New.
	(bfd_target): Add keep_unused_section_symbols.
	(bfd_keep_unused_section_symbols): New.
	* bfd-in2.h: Regenerated.

binutils/

	PR 27109
	* objcopy.c (copy_object): Handle section symbols for
	non-relocatable inputs.
	* testsuite/binutils-all/readelf.exp (readelf_test): Check
	is_elf_unused_section_symbols.
	* testsuite/binutils-all/readelf.s-64: Updated.
	* testsuite/binutils-all/readelf.ss: Likewise.
	* testsuite/binutils-all/readelf.ss-64: Likewise.
	* testsuite/binutils-all/readelf.s-64-unused: New file.
	* testsuite/binutils-all/readelf.ss-64-unused: Likewise.
	* testsuite/binutils-all/readelf.ss-unused: Likewise.
	* testsuite/lib/binutils-common.exp
	(is_elf_unused_section_symbols): New proc.

gas/ChangeLog:

	PR 27109
	* read.c (s_reloc): Call symbol_mark_used_in_reloc on the
	section symbol.
	* subsegs.c (subseg_set_rest): Set BSF_SECTION_SYM_USED if needed.
	* write.c (adjust_reloc_syms): Call symbol_mark_used_in_reloc
	on the section symbol.
	(set_symtab): Don't generate unused section symbols.
	(maybe_generate_build_notes): Call symbol_mark_used_in_reloc
	on the section symbol.
	* config/obj-elf.c (elf_adjust_symtab): Call
	symbol_mark_used_in_reloc on the group signature symbol.
	* testsuite/gas/cfi/cfi-label.d: Remove unused section symbols
	from expected output.
	* testsuite/gas/elf/elf.exp (run_elf_list_test): Check
	is_elf_unused_section_symbols.
	* testsuite/gas/elf/section2.e: Updated.
	* testsuite/gas/elf/section2.e-unused: New file.
	* testsuite/gas/elf/symver.d: Remove unused section symbols.
	* testsuite/gas/i386/ilp32/elf/symver.d: Likewise.
	* testsuite/gas/i386/ilp32/x86-64-size-1.d: Likewise.
	* testsuite/gas/i386/ilp32/x86-64-size-3.d: Likewise.
	* testsuite/gas/i386/ilp32/x86-64-size-5.d: Likewise.
	* testsuite/gas/i386/ilp32/x86-64-unwind.d: Likewise.
	* testsuite/gas/i386/size-1.d: Likewise.
	* testsuite/gas/i386/size-3.d: Likewise.
	* testsuite/gas/i386/svr4.d: Likewise.
	* testsuite/gas/i386/x86-64-size-1.d: Likewise.
	* testsuite/gas/i386/x86-64-size-3.d: Likewise.
	* testsuite/gas/i386/x86-64-size-5.d: Likewise.
	* testsuite/gas/i386/x86-64-unwind.d: Likewise.

ld/

	PR 27109
	* testsuite/ld-elf/export-class.sd: Adjust the expected output.
	* testsuite/ld-elf/loadaddr3b.d: Likewise.
	* testsuite/ld-i386/ibt-plt-1.d: Likewise.
	* testsuite/ld-i386/ibt-plt-2a.d: Likewise.
	* testsuite/ld-i386/ibt-plt-2c.d: Likewise.
	* testsuite/ld-i386/ibt-plt-3a.d: Likewise.
	* testsuite/ld-i386/ibt-plt-3c.d: Likewise.
	* testsuite/ld-i386/pr19636-1d.d: Likewise.
	* testsuite/ld-i386/pr19636-1l.d: Likewise.
	* testsuite/ld-i386/pr19636-2c.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-i386-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-local-i386-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-local-x86-64-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-x86-64-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-21-x86-64.d: Likewise.
	* testsuite/ld-ifunc/ifunc-22-x86-64.d: Likewise.
	* testsuite/ld-ifunc/pr17154-i386-now.d: Likewise.
	* testsuite/ld-ifunc/pr17154-i386.d: Likewise.
	* testsuite/ld-ifunc/pr17154-x86-64-now.d: Likewise.
	* testsuite/ld-ifunc/pr17154-x86-64.d: Likewise.
	* testsuite/ld-x86-64/bnd-branch-1-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-1-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-2-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-2.d: Likewise.
	* testsuite/ld-x86-64/bnd-plt-1-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-plt-1.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-1-x32.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-1.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-2a-x32.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-2a.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-2c-x32.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-2c.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-3a-x32.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-3a.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-3c-x32.d: Likewise.
	* testsuite/ld-x86-64/ibt-plt-3c.d: Likewise.
	* testsuite/ld-x86-64/pr19609-4e.d: Likewise.
	* testsuite/ld-x86-64/pr19609-6a.d: Likewise.
	* testsuite/ld-x86-64/pr19609-6b.d: Likewise.
	* testsuite/ld-x86-64/pr19609-7b.d: Likewise.
	* testsuite/ld-x86-64/pr19609-7d.d: Likewise.
	* testsuite/ld-x86-64/pr19636-2l.d: Likewise.
	* testsuite/ld-x86-64/pr20253-1d.d: Likewise.
	* testsuite/ld-x86-64/pr20253-1h.d: Likewise.
	* testsuite/ld-x86-64/pr21038b-now.d: Likewise.
	* testsuite/ld-x86-64/pr21038b.d: Likewise.
	* testsuite/ld-x86-64/pr21038c-now.d: Likewise.
	* testsuite/ld-x86-64/pr21038c.d: Likewise.
	* testsuite/ld-x86-64/pr23854.d: Likewise.
	* testsuite/ld-x86-64/pr25416-3.d: Likewise.
	* testsuite/ld-x86-64/pr25416-4.d: Likewise.
	* testsuite/ld-i386/plt-pic.pd: Likewise.
	* testsuite/ld-i386/plt-pic2.dd: Likewise.
	* testsuite/ld-i386/plt.pd: Likewise.
	* testsuite/ld-i386/plt2.dd: Likewise.
	* testsuite/ld-i386/tlsbin.rd: Likewise.
	* testsuite/ld-i386/tlsbin2.rd: Likewise.
	* testsuite/ld-i386/tlsbindesc.rd: Likewise.
	* testsuite/ld-i386/tlsdesc.rd: Likewise.
	* testsuite/ld-i386/tlsgdesc.rd: Likewise.
	* testsuite/ld-i386/tlsnopic.rd: Likewise.
	* testsuite/ld-i386/tlspic.rd: Likewise.
	* testsuite/ld-i386/tlspic2.rd: Likewise.
	* testsuite/ld-x86-64/mpx3.dd: Likewise.
	* testsuite/ld-x86-64/mpx3n.dd: Likewise.
	* testsuite/ld-x86-64/mpx4.dd: Likewise.
	* testsuite/ld-x86-64/mpx4n.dd: Likewise.
	* testsuite/ld-x86-64/pe-x86-64-1.od: Likewise.
	* testsuite/ld-x86-64/pe-x86-64-2.od: Likewise.
	* testsuite/ld-x86-64/pe-x86-64-3.od: Likewise.
	* testsuite/ld-x86-64/pe-x86-64-4.od: Likewise.
	* testsuite/ld-x86-64/plt.pd: Likewise.
	* testsuite/ld-x86-64/plt2.dd: Likewise.
	* testsuite/ld-x86-64/tlsbin.rd: Likewise.
	* testsuite/ld-x86-64/tlsbin2.rd: Likewise.
	* testsuite/ld-x86-64/tlsbindesc.rd: Likewise.
	* testsuite/ld-x86-64/tlsdesc.rd: Likewise.
	* testsuite/ld-x86-64/tlsgdesc.rd: Likewise.
	* testsuite/ld-x86-64/tlspic.rd: Likewise.
	* testsuite/ld-x86-64/tlspic2.rd: Likewise.
	* testsuite/ld-elf/sec64k.exp: Check
	is_elf_unused_section_symbols.
2021-01-07 06:46:55 -08:00

335 lines
8.3 KiB
C
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

/* subsegs.c - subsegments -
Copyright (C) 1987-2021 Free Software Foundation, Inc.
This file is part of GAS, the GNU Assembler.
GAS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GAS is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GAS; see the file COPYING. If not, write to the Free
Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
02110-1301, USA. */
/* Segments & sub-segments. */
#include "as.h"
#include "subsegs.h"
#include "obstack.h"
frchainS *frchain_now;
static struct obstack frchains;
static fragS dummy_frag;
void
subsegs_begin (void)
{
obstack_begin (&frchains, chunksize);
#if __GNUC__ >= 2
obstack_alignment_mask (&frchains) = __alignof__ (frchainS) - 1;
#endif
frchain_now = NULL; /* Warn new_subseg() that we are booting. */
frag_now = &dummy_frag;
}
/*
* subseg_change()
*
* Change the subsegment we are in, BUT DO NOT MAKE A NEW FRAG for the
* subsegment. If we are already in the correct subsegment, change nothing.
* This is used eg as a worker for subseg_set [which does make a new frag_now]
* and for changing segments after we have read the source. We construct eg
* fixSs even after the source file is read, so we do have to keep the
* segment context correct.
*/
void
subseg_change (segT seg, int subseg)
{
segment_info_type *seginfo = seg_info (seg);
now_seg = seg;
now_subseg = subseg;
if (! seginfo)
{
seginfo = XCNEW (segment_info_type);
seginfo->bfd_section = seg;
bfd_set_section_userdata (seg, seginfo);
}
}
static void
subseg_set_rest (segT seg, subsegT subseg)
{
frchainS *frcP; /* crawl frchain chain */
frchainS **lastPP; /* address of last pointer */
frchainS *newP; /* address of new frchain */
segment_info_type *seginfo;
mri_common_symbol = NULL;
if (frag_now && frchain_now)
frchain_now->frch_frag_now = frag_now;
gas_assert (frchain_now == 0
|| frchain_now->frch_last == frag_now);
subseg_change (seg, (int) subseg);
seginfo = seg_info (seg);
/* Should the section symbol be kept? */
if (bfd_keep_unused_section_symbols (stdoutput))
seg->symbol->flags |= BSF_SECTION_SYM_USED;
/* Attempt to find or make a frchain for that subsection.
We keep the list sorted by subsection number. */
for (frcP = *(lastPP = &seginfo->frchainP);
frcP != NULL;
frcP = *(lastPP = &frcP->frch_next))
if (frcP->frch_subseg >= subseg)
break;
if (frcP == NULL || frcP->frch_subseg != subseg)
{
/* This should be the only code that creates a frchainS. */
newP = (frchainS *) obstack_alloc (&frchains, sizeof (frchainS));
newP->frch_subseg = subseg;
newP->fix_root = NULL;
newP->fix_tail = NULL;
obstack_begin (&newP->frch_obstack, chunksize);
#if __GNUC__ >= 2
obstack_alignment_mask (&newP->frch_obstack) = __alignof__ (fragS) - 1;
#endif
newP->frch_frag_now = frag_alloc (&newP->frch_obstack);
newP->frch_frag_now->fr_type = rs_fill;
newP->frch_cfi_data = NULL;
newP->frch_root = newP->frch_last = newP->frch_frag_now;
*lastPP = newP;
newP->frch_next = frcP;
frcP = newP;
}
frchain_now = frcP;
frag_now = frcP->frch_frag_now;
gas_assert (frchain_now->frch_last == frag_now);
}
/*
* subseg_set(segT, subsegT)
*
* If you attempt to change to the current subsegment, nothing happens.
*
* In: segT, subsegT code for new subsegment.
* frag_now -> incomplete frag for current subsegment.
* If frag_now==NULL, then there is no old, incomplete frag, so
* the old frag is not closed off.
*
* Out: now_subseg, now_seg updated.
* Frchain_now points to the (possibly new) struct frchain for this
* sub-segment.
*/
segT
subseg_get (const char *segname, int force_new)
{
segT secptr;
segment_info_type *seginfo;
const char *now_seg_name = now_seg ? bfd_section_name (now_seg) : 0;
if (!force_new
&& now_seg_name
&& (now_seg_name == segname
|| !strcmp (now_seg_name, segname)))
return now_seg;
if (!force_new)
secptr = bfd_make_section_old_way (stdoutput, segname);
else
secptr = bfd_make_section_anyway (stdoutput, segname);
seginfo = seg_info (secptr);
if (! seginfo)
{
secptr->output_section = secptr;
seginfo = XCNEW (segment_info_type);
seginfo->bfd_section = secptr;
bfd_set_section_userdata (secptr, seginfo);
}
return secptr;
}
segT
subseg_new (const char *segname, subsegT subseg)
{
segT secptr;
secptr = subseg_get (segname, 0);
subseg_set_rest (secptr, subseg);
return secptr;
}
/* Like subseg_new, except a new section is always created, even if
a section with that name already exists. */
segT
subseg_force_new (const char *segname, subsegT subseg)
{
segT secptr;
secptr = subseg_get (segname, 1);
subseg_set_rest (secptr, subseg);
return secptr;
}
void
subseg_set (segT secptr, subsegT subseg)
{
if (! (secptr == now_seg && subseg == now_subseg))
subseg_set_rest (secptr, subseg);
mri_common_symbol = NULL;
}
#ifndef obj_sec_sym_ok_for_reloc
#define obj_sec_sym_ok_for_reloc(SEC) 0
#endif
symbolS *
section_symbol (segT sec)
{
segment_info_type *seginfo = seg_info (sec);
symbolS *s;
if (seginfo == 0)
abort ();
if (seginfo->sym)
return seginfo->sym;
#ifndef EMIT_SECTION_SYMBOLS
#define EMIT_SECTION_SYMBOLS 1
#endif
if (! EMIT_SECTION_SYMBOLS || symbol_table_frozen)
{
/* Here we know it won't be going into the symbol table. */
s = symbol_create (sec->symbol->name, sec, &zero_address_frag, 0);
}
else
{
segT seg;
s = symbol_find (sec->symbol->name);
/* We have to make sure it is the right symbol when we
have multiple sections with the same section name. */
if (s == NULL
|| ((seg = S_GET_SEGMENT (s)) != sec
&& seg != undefined_section))
s = symbol_new (sec->symbol->name, sec, &zero_address_frag, 0);
else if (seg == undefined_section)
{
S_SET_SEGMENT (s, sec);
symbol_set_frag (s, &zero_address_frag);
}
}
S_CLEAR_EXTERNAL (s);
/* Use the BFD section symbol, if possible. */
if (obj_sec_sym_ok_for_reloc (sec))
symbol_set_bfdsym (s, sec->symbol);
else
symbol_get_bfdsym (s)->flags |= BSF_SECTION_SYM;
seginfo->sym = s;
return s;
}
/* Return whether the specified segment is thought to hold text. */
int
subseg_text_p (segT sec)
{
return (bfd_section_flags (sec) & SEC_CODE) != 0;
}
/* Return non zero if SEC has at least one byte of data. It is
possible that we'll return zero even on a non-empty section because
we don't know all the fragment types, and it is possible that an
fr_fix == 0 one still contributes data. Think of this as
seg_definitely_not_empty_p. */
int
seg_not_empty_p (segT sec ATTRIBUTE_UNUSED)
{
segment_info_type *seginfo = seg_info (sec);
frchainS *chain;
fragS *frag;
if (!seginfo)
return 0;
for (chain = seginfo->frchainP; chain; chain = chain->frch_next)
{
for (frag = chain->frch_root; frag; frag = frag->fr_next)
if (frag->fr_fix)
return 1;
if (obstack_next_free (&chain->frch_obstack)
!= chain->frch_last->fr_literal)
return 1;
}
return 0;
}
void
subsegs_print_statistics (FILE *file)
{
frchainS *frchp;
asection *s;
/* PR 20897 - check to see if the output bfd was actually created. */
if (stdoutput == NULL)
return;
fprintf (file, "frag chains:\n");
for (s = stdoutput->sections; s; s = s->next)
{
segment_info_type *seginfo;
/* Skip gas-internal sections. */
if (segment_name (s)[0] == '*')
continue;
seginfo = seg_info (s);
if (!seginfo)
continue;
for (frchp = seginfo->frchainP; frchp; frchp = frchp->frch_next)
{
int count = 0;
fragS *fragp;
for (fragp = frchp->frch_root; fragp; fragp = fragp->fr_next)
count++;
fprintf (file, "\n");
fprintf (file, "\t%p %-10s\t%10d frags\n", (void *) frchp,
segment_name (s), count);
}
}
}
/* end of subsegs.c */