[hjl@gnu-6 new-2]$ cat foo.s .data foo: .dc.a bar [hjl@gnu-6 new-2]$ make as -o foo.o foo.s ./ld -shared -o lib.so foo.o readelf -sW lib.so | grep "ABS $" 10: 0000000000000000 0 FILE LOCAL DEFAULT ABS [hjl@gnu-6 new-2]$ It comes from: https://sourceware.org/ml/binutils/2012-06/msg00016.html But it is useless for linker generated symbols.
How useful is adding add another NULL STT_FILE symbol before outputting linker generated symbols or symbols defined by linker scripts? Do we have a testcase to show it is necessary?
A NULL STT_FILE symbol is useful here: [hjl@gnu-6 pr17975]$ cat foo.s .data foo: .dc.a bar [hjl@gnu-6 pr17975]$ cat bar.s .data foo: .dc.a bar [hjl@gnu-6 pr17975]$ cat global.s .data .hidden foo .global foo foo: .dc.a bar [hjl@gnu-6 pr17975]$ make hidden.so as -o foo.o foo.s as -o bar.o bar.s as -o global.o global.s ./ld -shared -o hidden.so foo.o bar.o global.o readelf -sW hidden.so Symbol table '.dynsym' contains 6 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000002002f0 0 SECTION LOCAL DEFAULT 7 2: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 __bss_start 3: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 _edata 4: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 _end 5: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND bar Symbol table '.symtab' contains 20 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000000000e8 0 SECTION LOCAL DEFAULT 1 2: 0000000000000118 0 SECTION LOCAL DEFAULT 2 3: 00000000000001a8 0 SECTION LOCAL DEFAULT 3 4: 00000000000001c8 0 SECTION LOCAL DEFAULT 4 5: 0000000000000210 0 SECTION LOCAL DEFAULT 5 6: 0000000000200210 0 SECTION LOCAL DEFAULT 6 7: 00000000002002f0 0 SECTION LOCAL DEFAULT 7 8: 0000000000000000 0 FILE LOCAL DEFAULT ABS foo.o 9: 00000000002002f0 0 NOTYPE LOCAL DEFAULT 7 foo 10: 0000000000000000 0 FILE LOCAL DEFAULT ABS bar.o 11: 00000000002002f8 0 NOTYPE LOCAL DEFAULT 7 foo 12: 0000000000000000 0 FILE LOCAL DEFAULT ABS 13: 0000000000200210 0 OBJECT LOCAL DEFAULT 6 _DYNAMIC 14: 0000000000200300 0 NOTYPE LOCAL DEFAULT 7 foo 15: 00000000002002f0 0 OBJECT LOCAL DEFAULT 7 _GLOBAL_OFFSET_TABLE_ 16: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 __bss_start 17: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 _edata 18: 0000000000200308 0 NOTYPE GLOBAL DEFAULT 7 _end 19: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND bar [hjl@gnu-6 pr17975]$ But not here [hjl@gnu-6 pr17975]$ make lib.so ./ld -shared -o lib.so foo.o bar.o readelf -sW lib.so Symbol table '.dynsym' contains 6 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000002002d8 0 SECTION LOCAL DEFAULT 7 2: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 __bss_start 3: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 _edata 4: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 _end 5: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND bar Symbol table '.symtab' contains 19 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000000000e8 0 SECTION LOCAL DEFAULT 1 2: 0000000000000118 0 SECTION LOCAL DEFAULT 2 3: 00000000000001a8 0 SECTION LOCAL DEFAULT 3 4: 00000000000001c8 0 SECTION LOCAL DEFAULT 4 5: 00000000000001f8 0 SECTION LOCAL DEFAULT 5 6: 00000000002001f8 0 SECTION LOCAL DEFAULT 6 7: 00000000002002d8 0 SECTION LOCAL DEFAULT 7 8: 0000000000000000 0 FILE LOCAL DEFAULT ABS foo.o 9: 00000000002002d8 0 NOTYPE LOCAL DEFAULT 7 foo 10: 0000000000000000 0 FILE LOCAL DEFAULT ABS bar.o 11: 00000000002002e0 0 NOTYPE LOCAL DEFAULT 7 foo 12: 0000000000000000 0 FILE LOCAL DEFAULT ABS 13: 00000000002001f8 0 OBJECT LOCAL DEFAULT 6 _DYNAMIC 14: 00000000002002d8 0 OBJECT LOCAL DEFAULT 7 _GLOBAL_OFFSET_TABLE_ 15: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 __bss_start 16: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 _edata 17: 00000000002002e8 0 NOTYPE GLOBAL DEFAULT 7 _end 18: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND bar [hjl@gnu-6 pr17975]$
We should generate a A NULL STT_FILE symbol before a forced_local symbol which isn't linker created nor defined by linker script.
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=35f82954b5e46ef5f56653d4f3aa0d1236f558da commit 35f82954b5e46ef5f56653d4f3aa0d1236f558da Author: H.J. Lu <hjl.tools@gmail.com> Date: Sat Feb 14 20:17:28 2015 -0800 Properly place the NULL STT_FILE symbol We output a NULL STT_FILE symbol for forced local symbols so that they are not associated with the STT_FILE symbol for real local symbols. This patch makes sure that the NULL STT_FILE symbol is placed before forced local symbols. bfd/ PR ld/17975 * elflink.c (elf_link_output_extsym): Only check filesym_count when outputting a NULL FILE symbol. Set second_pass_sym to h->forced_local && !h->root.linker_def. ld/testsuite/ PR ld/17975 * ld-i386/tlsbin-nacl.rd: Likewise. * ld-i386/tlsbin.rd: Likewise. * ld-i386/tlsbindesc-nacl.rd: Likewise. * ld-i386/tlsbindesc.rd: Likewise. * ld-i386/tlsdesc-nacl.rd: Likewise. * ld-i386/tlsdesc.rd: Likewise. * ld-i386/tlsnopic-nacl.rd: Likewise. * ld-i386/tlsnopic.rd: Likewise. * ld-i386/tlspic-nacl.rd: Likewise. * ld-i386/tlspic.rd: Likewise. * ld-x86-64/tlsbin-nacl.rd: Likewise. * ld-x86-64/tlsbin.rd: Likewise. * ld-x86-64/tlsbindesc-nacl.rd: Likewise. * ld-x86-64/tlsbindesc.rd: Likewise. * ld-x86-64/tlsdesc-nacl.rd: Likewise. * ld-x86-64/tlsdesc.rd: Likewise. * ld-x86-64/tlspic-nacl.rd: Likewise. * ld-x86-64/tlspic.rd: 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=6dfb72b9068626cbbf0017df092162d11304a3b0 commit 6dfb72b9068626cbbf0017df092162d11304a3b0 Author: H.J. Lu <hjl.tools@gmail.com> Date: Mon Feb 16 07:31:46 2015 -0800 Add ChangeLog entries for PR ld/17975 fix
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=49bd1d6e875d4b9ab0cdb909ae6db2bfc95f364b commit 49bd1d6e875d4b9ab0cdb909ae6db2bfc95f364b Author: H.J. Lu <hjl.tools@gmail.com> Date: Mon Feb 16 08:35:17 2015 -0800 Update more ld testcases after PR ld/17975 fix * ld-alpha/tlspic.rd: Updated. * ld-powerpc/tlsexe.r: Likewise. * ld-powerpc/tlsexetoc.r: Likewise. * ld-powerpc/tlsso.r: Likewise. * ld-powerpc/tlstocso.r: Likewise. * ld-s390/tlspic.rd: Likewise. * ld-s390/tlspic_64.rd: Likewise. * ld-sparc/gotop32.dd: Likewise. * ld-sparc/gotop64.dd: Likewise. * ld-sparc/tlssunnopic32.rd: Likewise. * ld-sparc/tlssunnopic64.rd: Likewise. * ld-sparc/tlssunpic32.rd: Likewise. * ld-sparc/tlssunpic64.rd: Likewise. * ld-tic6x/shlib-1.rd: Likewise. * ld-tic6x/shlib-1b.rd: Likewise. * ld-tic6x/shlib-1r.rd: Likewise. * ld-tic6x/shlib-1rb.rd: Likewise. * ld-tic6x/shlib-noindex.rd: Likewise.
Fixed.
The master branch has been updated by Alan Modra <amodra@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2ec55de302e4a6c49a06c673c8262a119fa6226f commit 2ec55de302e4a6c49a06c673c8262a119fa6226f Author: Alan Modra <amodra@gmail.com> Date: Tue Feb 17 09:14:59 2015 +1030 Properly place the NULL STT_FILE symbol revistited I was having a little closer look at what is going on here and noticed that HJ unconditionally emits a NULL STT_FILE symbol before emitting forced local symbols. That means we really don't need a second pass over forced local symbols. The only reason for two passes is when some forced local symbol can be emitted before the NULL STT_FILE. So I set about removing the second pass, updating the testsuite all over again. It's also unnecessary to emit the NULL STT_FILE when no previous file symbol has been emitted. bfd/ PR ld/17975 * elflink.c (struct elf_outext_info): Remove need_second_pass and second_pass. (elf_link_output_extsym): Delete code handling second forced local pass. Move code emitting NULL STT_FILE symbol later, so that it can be omitted if forced local is stripped. Don't emit the NULL STT_FILE if no file symbols have been output. (bfd_elf_final_link): Remove second forced local pass. * elf32-ppc.c (add_stub_sym): Set linker_def on linker syms. (ppc_elf_size_dynamic_sections): Likewise. * elf64-ppc.c (ppc_build_one_stub): Likewise. (build_global_entry_stubs): Likewise. (ppc64_elf_build_stubs): Likewise. ld/testsuite/ PR ld/17975 * ld-aarch64/gc-tls-relocs.d, * ld-alpha/tlspic.rd, * ld-cris/libdso-2.d, * ld-i386/tlsdesc-nacl.rd, * ld-i386/tlsdesc.rd, * ld-i386/tlsnopic-nacl.rd, * ld-i386/tlsnopic.rd, * ld-i386/tlspic-nacl.rd, * ld-i386/tlspic.rd, * ld-ia64/tlspic.rd, * ld-powerpc/tlsexe.r, * ld-powerpc/tlsexetoc.r, * ld-powerpc/tlsso.r, * ld-powerpc/tlstocso.r, * ld-s390/tlspic.rd, * ld-s390/tlspic_64.rd, * ld-sparc/tlssunnopic32.rd, * ld-sparc/tlssunnopic64.rd, * ld-sparc/tlssunpic32.rd, * ld-sparc/tlssunpic64.rd, * ld-tic6x/shlib-1.rd, * ld-tic6x/shlib-1b.rd, * ld-tic6x/shlib-1r.rd, * ld-tic6x/shlib-1rb.rd, * ld-tic6x/shlib-noindex.rd, * ld-x86-64/tlsdesc-nacl.rd, * ld-x86-64/tlsdesc.rd, * ld-x86-64/tlspic-nacl.rd, * ld-x86-64/tlspic.rd: Update.