From cf1509c67f6c2ca0919c60220489e8d10bb4963a Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 12 May 2015 16:52:11 -0700 Subject: [PATCH] Add -mshared option to x86 ELF assembler This patch adds -mshared option to x86 ELF assembler. By default, assembler will optimize out relocations to defined non-weak global branch targets with default visibility. The -mshared option tells the assembler to generate code which may go into a shared library where all non-weak global branch targets with default visibility can be preempted. The resulting code is slightly bigger. This option only affects the handling of branch instructions. gas/ * config/tc-i386.c (shared): New. (OPTION_MSHARED): Likewise. (elf_symbol_resolved_in_segment_p): Add relocation argument. Check PLT relocations and shared. (md_estimate_size_before_relax): Pass fragP->fr_var to elf_symbol_resolved_in_segment_p. (md_longopts): Add -mshared. (md_show_usage): Likewise. (md_parse_option): Handle OPTION_MSHARED. * doc/c-i386.texi: Document -mshared. gas/testsuite/ * gas/i386/i386.exp: Run relax-4 and x86-64-relax-3. * gas/i386/pcrel.d: Pass -mshared to assembler. * gas/i386/relax-3.d: Likewise. Updated. * gas/i386/x86-64-relax-2.d: Likewise. * gas/i386/relax-3.s: Add test for PLT relocation. * gas/i386/relax-4.d: New file. * gas/i386/x86-64-relax-3.d: Likewise. --- gas/config/tc-i386.c | 35 ++++++++++++++++++++++++++++++--- gas/doc/c-i386.texi | 11 +++++++++++ gas/testsuite/gas/i386/i386.exp | 2 ++ gas/testsuite/gas/i386/pcrel.d | 1 + gas/testsuite/gas/i386/relax-3.d | 28 ++++++++++++++------------ gas/testsuite/gas/i386/relax-3.s | 1 + gas/testsuite/gas/i386/relax-4.d | 32 ++++++++++++++++++++++++++++++ gas/testsuite/gas/i386/x86-64-relax-2.d | 24 +++++++++++----------- gas/testsuite/gas/i386/x86-64-relax-3.d | 33 +++++++++++++++++++++++++++++++ 9 files changed, 140 insertions(+), 27 deletions(-) create mode 100644 gas/testsuite/gas/i386/relax-4.d create mode 100644 gas/testsuite/gas/i386/x86-64-relax-3.d diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c index 75f268f..254548f 100644 --- a/gas/config/tc-i386.c +++ b/gas/config/tc-i386.c @@ -524,6 +524,11 @@ static enum x86_elf_abi x86_elf_abi = I386_ABI; static int use_big_obj = 0; #endif +#if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF) +/* 1 if generating code for a shared library. */ +static int shared = 0; +#endif + /* 1 for intel syntax, 0 if att syntax. */ static int intel_syntax = 0; @@ -8818,7 +8823,7 @@ i386_frag_max_var (fragS *frag) #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF) static int -elf_symbol_resolved_in_segment_p (symbolS *fr_symbol) +elf_symbol_resolved_in_segment_p (symbolS *fr_symbol, offsetT fr_var) { /* STT_GNU_IFUNC symbol must go through PLT. */ if ((symbol_get_bfdsym (fr_symbol)->flags @@ -8829,9 +8834,24 @@ elf_symbol_resolved_in_segment_p (symbolS *fr_symbol) /* Symbol may be weak or local. */ return !S_IS_WEAK (fr_symbol); + /* Global symbols with non-default visibility can't be preempted. */ + if (ELF_ST_VISIBILITY (S_GET_OTHER (fr_symbol)) != STV_DEFAULT) + return 1; + + if (fr_var != NO_RELOC) + switch ((enum bfd_reloc_code_real) fr_var) + { + case BFD_RELOC_386_PLT32: + case BFD_RELOC_X86_64_PLT32: + /* Symbol with PLT relocatin may be preempted. */ + return 0; + default: + abort (); + } + /* Global symbols with default visibility in a shared library may be preempted by another definition. */ - return ELF_ST_VISIBILITY (S_GET_OTHER (fr_symbol)) != STV_DEFAULT; + return !shared; } #endif @@ -8858,7 +8878,8 @@ md_estimate_size_before_relax (fragS *fragP, segT segment) if (S_GET_SEGMENT (fragP->fr_symbol) != segment #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF) || (IS_ELF - && !elf_symbol_resolved_in_segment_p (fragP->fr_symbol)) + && !elf_symbol_resolved_in_segment_p (fragP->fr_symbol, + fragP->fr_var)) #endif #if defined (OBJ_COFF) && defined (TE_PE) || (OUTPUT_FLAVOR == bfd_target_coff_flavour @@ -9528,6 +9549,7 @@ const char *md_shortopts = "qn"; #define OPTION_MBIG_OBJ (OPTION_MD_BASE + 18) #define OPTION_OMIT_LOCK_PREFIX (OPTION_MD_BASE + 19) #define OPTION_MEVEXRCIG (OPTION_MD_BASE + 20) +#define OPTION_MSHARED (OPTION_MD_BASE + 21) struct option md_longopts[] = { @@ -9538,6 +9560,7 @@ struct option md_longopts[] = #endif #if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF) {"x32", no_argument, NULL, OPTION_X32}, + {"mshared", no_argument, NULL, OPTION_MSHARED}, #endif {"divide", no_argument, NULL, OPTION_DIVIDE}, {"march", required_argument, NULL, OPTION_MARCH}, @@ -9598,6 +9621,10 @@ md_parse_option (int c, char *arg) /* -s: On i386 Solaris, this tells the native assembler to use .stab instead of .stab.excl. We always use .stab anyhow. */ break; + + case OPTION_MSHARED: + shared = 1; + break; #endif #if (defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF) \ || defined (TE_PE) || defined (TE_PEP) || defined (OBJ_MACH_O)) @@ -10027,6 +10054,8 @@ md_show_usage (FILE *stream) -mold-gcc support old (<= 2.8.1) versions of gcc\n")); fprintf (stream, _("\ -madd-bnd-prefix add BND prefix for all valid branches\n")); + fprintf (stream, _("\ + -mshared disable branch optimization for shared code\n")); # if defined (TE_PE) || defined (TE_PEP) fprintf (stream, _("\ -mbig-obj generate big object files\n")); diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi index 1645c8c..a1997f5 100644 --- a/gas/doc/c-i386.texi +++ b/gas/doc/c-i386.texi @@ -298,6 +298,17 @@ The @code{.att_syntax} and @code{.intel_syntax} directives will take precedent. This option forces the assembler to add BND prefix to all branches, even if such prefix was not explicitly specified in the source code. +@cindex @samp{-mshared} option, i386 +@cindex @samp{-mshared} option, x86-64 +@item -mno-shared +On ELF target, the assembler normally optimizes out relocations to +defined non-weak global branch targets with default visibility. The +@samp{-mshared} option tells the assembler to generate code which +may go into a shared library where all non-weak global branch targets +with default visibility can be preempted. The resulting code is +slightly bigger. This option only affects the handling of branch +instructions. + @cindex @samp{-mbig-obj} option, x86-64 @item -mbig-obj On x86-64 PE/COFF target this option forces the use of big object file diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp index b6f2810..c66dbc5 100644 --- a/gas/testsuite/gas/i386/i386.exp +++ b/gas/testsuite/gas/i386/i386.exp @@ -396,6 +396,7 @@ if [expr ([istarget "i*86-*-*"] || [istarget "x86_64-*-*"]) && [gas_32_check]] run_dump_test "note" run_dump_test "relax-3" + run_dump_test "relax-4" if {![istarget "*-*-nacl*"]} then { run_dump_test "iamcu-1" @@ -763,6 +764,7 @@ if [expr ([istarget "i*86-*-*"] || [istarget "x86_64-*-*"]) && [gas_64_check]] t run_list_test "x86-64-size-inval-1" "-al" run_dump_test "x86-64-relax-2" + run_dump_test "x86-64-relax-3" run_dump_test "x86-64-jump" } diff --git a/gas/testsuite/gas/i386/pcrel.d b/gas/testsuite/gas/i386/pcrel.d index 5b61c23..8a91a1a 100644 --- a/gas/testsuite/gas/i386/pcrel.d +++ b/gas/testsuite/gas/i386/pcrel.d @@ -1,4 +1,5 @@ #objdump: -drw +#as: -mshared #name: i386 pcrel reloc .*: +file format .*i386.* diff --git a/gas/testsuite/gas/i386/relax-3.d b/gas/testsuite/gas/i386/relax-3.d index 8aa94e9..4610553 100644 --- a/gas/testsuite/gas/i386/relax-3.d +++ b/gas/testsuite/gas/i386/relax-3.d @@ -1,3 +1,4 @@ +#as: -mshared #objdump: -dwr .*: +file format .* @@ -5,26 +6,27 @@ Disassembly of section .text: 0+ : -[ ]*[a-f0-9]+: eb 1f jmp 21 -[ ]*[a-f0-9]+: eb 19 jmp 1d -[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 5 5: (R_386_PC)?(DISP)?32 global_def -[ ]*[a-f0-9]+: e9 fc ff ff ff jmp a a: (R_386_PC)?(DISP)?32 weak_def -[ ]*[a-f0-9]+: e9 fc ff ff ff jmp f f: (R_386_PC)?(DISP)?32 weak_hidden_undef -[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 14 14: (R_386_PC)?(DISP)?32 weak_hidden_def -[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 19 19: (R_386_PC)?(DISP)?32 hidden_undef - -0+1d : +[ ]*[a-f0-9]+: eb 24 jmp 26 +[ ]*[a-f0-9]+: eb 1e jmp 22 +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 5 5: R_386_PC32 global_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp a a: R_386_PLT32 global_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp f f: R_386_PC32 weak_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 14 14: R_386_PC32 weak_hidden_undef +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 19 19: R_386_PC32 weak_hidden_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 1e 1e: R_386_PC32 hidden_undef + +0+22 : [ ]*[a-f0-9]+: c3 ret -0+1e : +0+23 : [ ]*[a-f0-9]+: c3 ret -0+1f : +0+24 : [ ]*[a-f0-9]+: c3 ret -0+20 : +0+25 : [ ]*[a-f0-9]+: c3 ret -0+21 : +0+26 : [ ]*[a-f0-9]+: c3 ret #pass diff --git a/gas/testsuite/gas/i386/relax-3.s b/gas/testsuite/gas/i386/relax-3.s index ab52185..48ea917 100644 --- a/gas/testsuite/gas/i386/relax-3.s +++ b/gas/testsuite/gas/i386/relax-3.s @@ -4,6 +4,7 @@ foo: jmp local jmp hidden_def jmp global_def + jmp global_def@PLT jmp weak_def jmp weak_hidden_undef jmp weak_hidden_def diff --git a/gas/testsuite/gas/i386/relax-4.d b/gas/testsuite/gas/i386/relax-4.d new file mode 100644 index 0000000..2039251 --- /dev/null +++ b/gas/testsuite/gas/i386/relax-4.d @@ -0,0 +1,32 @@ +#source: relax-3.s +#objdump: -dwr + +.*: +file format .* + +Disassembly of section .text: + +0+ : +[ ]*[a-f0-9]+: eb 21 jmp 23 +[ ]*[a-f0-9]+: eb 1b jmp 1f +[ ]*[a-f0-9]+: eb 1b jmp 21 +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 7 7: R_386_PLT32 global_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp c c: R_386_PC32 weak_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 11 11: R_386_PC32 weak_hidden_undef +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 16 16: R_386_PC32 weak_hidden_def +[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 1b 1b: R_386_PC32 hidden_undef + +0+1f : +[ ]*[a-f0-9]+: c3 ret + +0+20 : +[ ]*[a-f0-9]+: c3 ret + +0+21 : +[ ]*[a-f0-9]+: c3 ret + +0+22 : +[ ]*[a-f0-9]+: c3 ret + +0+23 : +[ ]*[a-f0-9]+: c3 ret +#pass diff --git a/gas/testsuite/gas/i386/x86-64-relax-2.d b/gas/testsuite/gas/i386/x86-64-relax-2.d index 7b0bd56..c124102 100644 --- a/gas/testsuite/gas/i386/x86-64-relax-2.d +++ b/gas/testsuite/gas/i386/x86-64-relax-2.d @@ -1,4 +1,5 @@ #source: relax-3.s +#as: -mshared #objdump: -dwr .*: +file format .* @@ -7,26 +8,27 @@ Disassembly of section .text: 0+ : -[ ]*[a-f0-9]+: eb 1f jmp 21 -[ ]*[a-f0-9]+: eb 19 jmp 1d +[ ]*[a-f0-9]+: eb 24 jmp 26 +[ ]*[a-f0-9]+: eb 1e jmp 22 [ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 9 5: R_X86_64_PC32 global_def-0x4 -[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq e a: R_X86_64_PC32 weak_def-0x4 -[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 13 f: R_X86_64_PC32 weak_hidden_undef-0x4 -[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 18 14: R_X86_64_PC32 weak_hidden_def-0x4 -[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1d 19: R_X86_64_PC32 hidden_undef-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq e a: R_X86_64_PLT32 global_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 13 f: R_X86_64_PC32 weak_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 18 14: R_X86_64_PC32 weak_hidden_undef-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1d 19: R_X86_64_PC32 weak_hidden_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 22 1e: R_X86_64_PC32 hidden_undef-0x4 -0+1d : +0+22 : [ ]*[a-f0-9]+: c3 retq -0+1e : +0+23 : [ ]*[a-f0-9]+: c3 retq -0+1f : +0+24 : [ ]*[a-f0-9]+: c3 retq -0+20 : +0+25 : [ ]*[a-f0-9]+: c3 retq -0+21 : +0+26 : [ ]*[a-f0-9]+: c3 retq #pass diff --git a/gas/testsuite/gas/i386/x86-64-relax-3.d b/gas/testsuite/gas/i386/x86-64-relax-3.d new file mode 100644 index 0000000..98fd28d --- /dev/null +++ b/gas/testsuite/gas/i386/x86-64-relax-3.d @@ -0,0 +1,33 @@ +#source: relax-3.s +#objdump: -dwr + +.*: +file format .* + + +Disassembly of section .text: + +0+ : +[ ]*[a-f0-9]+: eb 21 jmp 23 +[ ]*[a-f0-9]+: eb 1b jmp 1f +[ ]*[a-f0-9]+: eb 1b jmp 21 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq b 7: R_X86_64_PLT32 global_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 10 c: R_X86_64_PC32 weak_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 15 11: R_X86_64_PC32 weak_hidden_undef-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1a 16: R_X86_64_PC32 weak_hidden_def-0x4 +[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1f 1b: R_X86_64_PC32 hidden_undef-0x4 + +0+1f : +[ ]*[a-f0-9]+: c3 retq + +0+20 : +[ ]*[a-f0-9]+: c3 retq + +0+21 : +[ ]*[a-f0-9]+: c3 retq + +0+22 : +[ ]*[a-f0-9]+: c3 retq + +0+23 : +[ ]*[a-f0-9]+: c3 retq +#pass -- 2.1.0