(originally mentioned in bug 21557) Linker manual explicitly states that __start_SCN symbols are automatically provided only for orphan sections. However, the following testcase shows that such symbols appear virtually present when marking reachable sections for --gc-sections: cat <<EOF >test.s .section scnfoo,"aw",@progbits .zero 1 .globl bar .data .align 8 .type bar, @object .size bar, 8 bar: .quad __start_scnfoo EOF cat <<EOF >lds SECTIONS { scnfoo : { *(scnfoo) } } EOF $ ld.bfd -shared -o test.so test.o --gc-sections --print-gc-sections -T lds <no output, scnfoo not eliminated, __start_scnfoo is undefined>
_bfd_elf_gc_mark_rsec has if (start_stop != NULL) { /* To work around a glibc bug, mark all XXX input sections when there is an as yet undefined reference to __start_XXX or __stop_XXX symbols. The linker will later define such symbols for orphan input sections that have a name representable as a C identifier. */ asection *s = _bfd_elf_is_start_stop (info, h); if (s != NULL) { *start_stop = !s->gc_mark; return s; } } The question is if ELF linker automatically creates a definition when there is a reference, regardless if the input section is orphan or not.
Created attachment 10084 [details] Try this
Created attachment 10085 [details] A better patch
Created attachment 10088 [details] A new patch
The patch looks wrong, it appears to ensure that __start_scnfoo is defined. The linker manual says it shouldn't get defined (scnfoo is not orphan), and therefore scnfoo should be eliminated due to --gc-sections. (note that bug 20022 and bug 19167 are both for orphan sections, linker scripts are not involved there)
(In reply to Alexander Monakov from comment #5) > The patch looks wrong, it appears to ensure that __start_scnfoo is defined. > The linker manual says it shouldn't get defined (scnfoo is not orphan), and > therefore scnfoo should be eliminated due to --gc-sections. > I posted a patch to always define referenced __start_SECNAME/__stop_SECNAME: https://sourceware.org/ml/binutils/2017-06/msg00105.html
(In reply to H.J. Lu from comment #6) > I posted a patch to always define referenced __start_SECNAME/__stop_SECNAME: That's quite confusing, because originally bug 21557 (wrongly) complained about those symbols not being defined, and you closed that bug as WONTFIX. If you changed your mind, can you please update that bug? I don't see the reason to extend __start_SECNAME auto-provisioning, it seems it would be simpler to avoid extraneous gc-marking shown in this bug.
(In reply to Alexander Monakov from comment #7) > (In reply to H.J. Lu from comment #6) > > I posted a patch to always define referenced __start_SECNAME/__stop_SECNAME: > > That's quite confusing, because originally bug 21557 (wrongly) complained > about those symbols not being defined, and you closed that bug as WONTFIX. > If you changed your mind, can you please update that bug? I will update it after my patch has been checked in. > I don't see the reason to extend __start_SECNAME auto-provisioning, it seems > it would be simpler to avoid extraneous gc-marking shown in this bug. The new approach is faster and happens to support non-orphaned sections.
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=cbd0eecf261c2447781f8c89b0d955ee66fae7e9 commit cbd0eecf261c2447781f8c89b0d955ee66fae7e9 Author: H.J. Lu <hjl.tools@gmail.com> Date: Tue Jun 13 08:53:22 2017 -0700 Always define referenced __start_SECNAME/__stop_SECNAME Currently, linker will define __start_SECNAME and __stop_SECNAME symbols only for orphaned sections. However, during garbage collection, ELF linker marks all sections with references to __start_SECNAME and __stop_SECNAME symbols as used even when section SECNAME isn't an orphaned section and linker won't define __start_SECNAME nor __stop_SECNAME. And ELF linker stores the first input section whose name matches __start_SECNAME or __stop_SECNAME in u.undef.section for garbage collection. If these symbols are provided in linker script, u.undef.section is set to the section where they will defined by linker script, which leads to the incorrect output. This patch changes linker to always define referenced __start_SECNAME and __stop_SECNAME if the input section name is the same as the output section name, which is always true for orphaned sections, and SECNAME is a C identifier. Also __start_SECNAME and __stop_SECNAME symbols are marked as hidden by ELF linker so that __start_SECNAME and __stop_SECNAME symbols for section SECNAME in different modules are unique. For garbage collection, ELF linker stores the first matched input section in the unused vtable field. bfd/ PR ld/20022 PR ld/21557 PR ld/21562 PR ld/21571 * elf-bfd.h (elf_link_hash_entry): Add start_stop. Change the vtable field to a union. (_bfd_elf_is_start_stop): Removed. * elf32-i386.c (elf_i386_convert_load_reloc): Also check for __start_SECNAME and __stop_SECNAME symbols. * elf64-x86-64.c (elf_x86_64_convert_load_reloc): Likewise. * elflink.c (_bfd_elf_is_start_stop): Removed. (_bfd_elf_gc_mark_rsec): Check start_stop instead of calling _bfd_elf_is_start_stop. (elf_gc_propagate_vtable_entries_used): Skip __start_SECNAME and __stop_SECNAME symbols. Updated. (elf_gc_smash_unused_vtentry_relocs): Likewise. (bfd_elf_gc_record_vtinherit): Likewise. (bfd_elf_gc_record_vtentry): Likewise. ld/ PR ld/20022 PR ld/21557 PR ld/21562 PR ld/21571 * ld.texinfo: Update __start_SECNAME/__stop_SECNAME symbols. * ldlang.c (lang_insert_orphan): Move handling of __start_SECNAME and __stop_SECNAME symbols to ... (lang_set_startof): Here. Also define __start_SECNAME and __stop_SECNAME for -Ur. * emultempl/elf32.em (gld${EMULATION_NAME}_after_open): Mark referenced __start_SECNAME and __stop_SECNAME symbols as hidden and set start_stop for garbage collection. * testsuite/ld-elf/pr21562a.d: New file. * testsuite/ld-elf/pr21562a.s: Likewise. * testsuite/ld-elf/pr21562a.t: Likewise. * testsuite/ld-elf/pr21562b.d: Likewise. * testsuite/ld-elf/pr21562b.s: Likewise. * testsuite/ld-elf/pr21562b.t: Likewise. * testsuite/ld-elf/pr21562c.d: Likewise. * testsuite/ld-elf/pr21562c.t: Likewise. * testsuite/ld-elf/pr21562d.d: Likewise. * testsuite/ld-elf/pr21562d.t: Likewise. * testsuite/ld-elf/pr21562e.d: Likewise. * testsuite/ld-elf/pr21562f.d: Likewise. * testsuite/ld-elf/pr21562g.d: Likewise. * testsuite/ld-elf/pr21562h.d: Likewise. * testsuite/ld-elf/pr21562i.d: Likewise. * testsuite/ld-elf/pr21562j.d: Likewise. * testsuite/ld-elf/pr21562k.d: Likewise. * testsuite/ld-elf/pr21562l.d: Likewise. * testsuite/ld-elf/pr21562m.d: Likewise. * testsuite/ld-elf/pr21562n.d: Likewise. * testsuite/ld-gc/pr20022.d: Likewise. * testsuite/ld-gc/pr20022a.s: Likewise. * testsuite/ld-gc/pr20022b.s: Likewise. * testsuite/ld-gc/gc.exp: Run PR ld/20022 tests. * testsuite/ld-gc/pr19161.d: Also accept local __start_SECNAME symbol. * testsuite/ld-gc/start.d: Likewise. * testsuite/ld-x86-64/lea1a.d: Updated. * testsuite/ld-x86-64/lea1b.d: Updated. * testsuite/ld-x86-64/lea1d.d: Updated. * testsuite/ld-x86-64/lea1e.d: Likewise.
Fixed.
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8eca1095d96c215409371c5687573aac89a0a980 commit 8eca1095d96c215409371c5687573aac89a0a980 Author: H.J. Lu <hjl.tools@gmail.com> Date: Wed Jun 14 04:36:17 2017 -0700 Skip PR ld/21562 tests on targets with leading char or without --gc-sections Symbol lookup in linker will always fail on targets with leading char in symbol name since __start_SECNAME and __stop_SECNAME in C may be ___start_SECNAME and ___stop_SECNAME in assembly. Also tests with --gc-sections always fails on targets without --gc-sections support. * testsuite/ld-elf/pr21562a.d: Skip on targets with leading char in in symbol name or without --gc-sections. * testsuite/ld-elf/pr21562b.d: Likewise. * testsuite/ld-elf/pr21562c.d: Likewise. * testsuite/ld-elf/pr21562d.d: Likewise. * testsuite/ld-elf/pr21562i.d: Likewise. * testsuite/ld-elf/pr21562j.d: Likewise. * testsuite/ld-elf/pr21562k.d: Likewise. * testsuite/ld-elf/pr21562l.d: Likewise. * testsuite/ld-elf/pr21562m.d: Likewise. * testsuite/ld-elf/pr21562n.d: Likewise. * testsuite/ld-elf/pr21562e.d: Skip on targets with leading char in symbol name. * testsuite/ld-elf/pr21562f.d: Likewise. * testsuite/ld-elf/pr21562g.d: Likewise. * testsuite/ld-elf/pr21562h.d: Likewise.
The master branch has been updated by Alan Modra <amodra@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7dba9362c172f1073487536eb137feb2da30b0ff commit 7dba9362c172f1073487536eb137feb2da30b0ff Author: Alan Modra <amodra@gmail.com> Date: Fri Jun 16 19:41:41 2017 +0930 Rewrite __start and __stop symbol handling This arranges for __start and __stop symbols to be defined before garbage collection, for all target formats. That should allow the COFF and PE --gc-sections to keep a singleton orphan input section, a feature lost by 2017-06-13 commit cbd0eecf26. The fancier ELF treatment of keeping all input sections associated with a __start or __stop symbol, from 2015-10-23 commit 1cce69b9dc, is retained. .startof. and .sizeof. symbols are deliberately not defined before garbage collection, so these won't affect garbage collection of sections. The patch also ensures __start, __stop, .startof. and .sizeof. symbols are defined before target size_dynamic_sections is called, albeit with a preliminary value, so that target code doesn't need to cope with a symbol changing from undefined at size_dynamic_sections to defined at relocate_section. Also, a number of problems with the testcases have been fixed. PR ld/20022 PR ld/21557 PR ld/21562 PR ld/21571 include/ * bfdlink.h (struct bfd_link_hash_entry): Delete undef.section. bfd/ * targets.c (struct bfd_target): Add _bfd_define_start_stop. (BFD_JUMP_TABLE_LINK): Likewise. * elf-bfd.h (bfd_elf_define_start_stop): Declare. * elflink.c (_bfd_elf_gc_mark_rsec): Update comment. (bfd_elf_define_start_stop): New function. * linker.c (bfd_generic_define_start_stop): New function. * coff64-rs6000.c (rs6000_xcoff64_vec, rs6000_xcoff64_aix_vec): Init new field. * aout-adobe.c (aout_32_bfd_define_start_stop): Define. * aout-target.h (MY_bfd_define_start_stop): Define. * aout-tic30.c (MY_bfd_define_start_stop): Define. * binary.c (binary_bfd_define_start_stop): Define. * bout.c (b_out_bfd_define_start_stop): Define. * coff-alpha.c (_bfd_ecoff_bfd_define_start_stop): Define. * coff-mips.c (_bfd_ecoff_bfd_define_start_stop): Define. * coff-rs6000.c (_bfd_xcoff_bfd_define_start_stop): Define. * coffcode.h (coff_bfd_define_start_stop): Define. * elfxx-target.h (bfd_elfNN_bfd_define_start_stop): Define. * i386msdos.c (msdos_bfd_define_start_stop): Define. * i386os9k.c (os9k_bfd_define_start_stop): Define. * ieee.c (ieee_bfd_define_start_stop): Define. * ihex.c (ihex_bfd_define_start_stop): Define. * libbfd-in.h (_bfd_nolink_bfd_define_start_stop): Define. * mach-o-target.c (bfd_mach_o_bfd_define_start_stop): Define. * mmo.c (mmo_bfd_define_start_stop): Define. * nlm-target.h (nlm_bfd_define_start_stop): Define. * oasys.c (oasys_bfd_define_start_stop): Define. * pef.c (bfd_pef_bfd_define_start_stop): Define. * plugin.c (bfd_plugin_bfd_define_start_stop): Define. * ppcboot.c (ppcboot_bfd_define_start_stop): Define. * som.c (som_bfd_define_start_stop): Define. * srec.c (srec_bfd_define_start_stop): Define. * tekhex.c (tekhex_bfd_define_start_stop): Define. * versados.c (versados_bfd_define_start_stop): Define. * vms-alpha.c (vms_bfd_define_start_stop): Define. (alpha_vms_bfd_define_start_stop): Define. * xsym.c (bfd_sym_bfd_define_start_stop): Define. * bfd-in2.h: Regenerate. * libbfd.h: Regenerate. ld/ * emultempl/elf32.em (gld${EMULATION_NAME}_after_open): Don't set __start/__stop syms here. * ldlang.c (lang_set_startof): Delete. (start_stop_syms, start_stop_count, start_stop_alloc): New vars. (lang_define_start_stop, lang_init_start_stop, foreach_start_stop, undef_start_stop, lang_undef_start_stop, lang_init_startof_sizeof, set_start_stop, lang_finalize_start_stop): New functions. (lang_process): Call _start_stop functions. * testsuite/ld-elf/pr21562a.d: Use xfail rather than notarget. Correct typos and list of xfail targets. * testsuite/ld-elf/pr21562b.d: Likewise. * testsuite/ld-elf/pr21562c.d: Likewise. * testsuite/ld-elf/pr21562d.d: Likewise. * testsuite/ld-elf/pr21562e.d: Likewise. * testsuite/ld-elf/pr21562f.d: Likewise. * testsuite/ld-elf/pr21562g.d: Likewise. * testsuite/ld-elf/pr21562h.d: Likewise. * testsuite/ld-elf/pr21562i.d: Likewise. * testsuite/ld-elf/pr21562j.d: Likewise. * testsuite/ld-elf/pr21562k.d: Likewise. * testsuite/ld-elf/pr21562l.d: Likewise. * testsuite/ld-elf/pr21562m.d: Likewise. * testsuite/ld-elf/pr21562n.d: Likewise. * testsuite/ld-elf/sizeofa.d: Likewise. Adjust to pass for generic ELF. * testsuite/ld-elf/sizeofb.d: Likewise. * testsuite/ld-elf/startofa.d: Likewise. * testsuite/ld-elf/startofb.d: Likewise.
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8b77421a20c22c9a66048e7d1484b149da060b67 commit 8b77421a20c22c9a66048e7d1484b149da060b67 Author: H.J. Lu <hjl.tools@gmail.com> Date: Fri Nov 24 08:58:43 2017 -0800 Update PR ld/21562 tests for underscore targets We also need to provide __start_scnfoo and __stop_scnfoo with the extra leading underscore for underscore targets. This patch fixed: FAIL: ld-elf/pr21562k FAIL: ld-elf/pr21562l FAIL: ld-elf/pr21562m FAIL: ld-elf/pr21562n for metag-linux, * testsuite/ld-elf/pr21562c.t: Also provide ___start_scnfoo and ___stop_scnfoo. * testsuite/ld-elf/pr21562d.t: Likewise.