From cf1509c67f6c2ca0919c60220489e8d10bb4963a Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
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+ <foo>:
-[ ]*[a-f0-9]+: eb 1f jmp 21 <local>
-[ ]*[a-f0-9]+: eb 19 jmp 1d <hidden_def>
-[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 5 <foo\+0x5> 5: (R_386_PC)?(DISP)?32 global_def
-[ ]*[a-f0-9]+: e9 fc ff ff ff jmp a <foo\+0xa> a: (R_386_PC)?(DISP)?32 weak_def
-[ ]*[a-f0-9]+: e9 fc ff ff ff jmp f <foo\+0xf> f: (R_386_PC)?(DISP)?32 weak_hidden_undef
-[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 14 <foo\+0x14> 14: (R_386_PC)?(DISP)?32 weak_hidden_def
-[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 19 <foo\+0x19> 19: (R_386_PC)?(DISP)?32 hidden_undef
-
-0+1d <hidden_def>:
+[ ]*[a-f0-9]+: eb 24 jmp 26 <local>
+[ ]*[a-f0-9]+: eb 1e jmp 22 <hidden_def>
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 5 <foo\+0x5> 5: R_386_PC32 global_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp a <foo\+0xa> a: R_386_PLT32 global_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp f <foo\+0xf> f: R_386_PC32 weak_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 14 <foo\+0x14> 14: R_386_PC32 weak_hidden_undef
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 19 <foo\+0x19> 19: R_386_PC32 weak_hidden_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 1e <foo\+0x1e> 1e: R_386_PC32 hidden_undef
+
+0+22 <hidden_def>:
[ ]*[a-f0-9]+: c3 ret
-0+1e <weak_hidden_def>:
+0+23 <weak_hidden_def>:
[ ]*[a-f0-9]+: c3 ret
-0+1f <global_def>:
+0+24 <global_def>:
[ ]*[a-f0-9]+: c3 ret
-0+20 <weak_def>:
+0+25 <weak_def>:
[ ]*[a-f0-9]+: c3 ret
-0+21 <local>:
+0+26 <local>:
[ ]*[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+ <foo>:
+[ ]*[a-f0-9]+: eb 21 jmp 23 <local>
+[ ]*[a-f0-9]+: eb 1b jmp 1f <hidden_def>
+[ ]*[a-f0-9]+: eb 1b jmp 21 <global_def>
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 7 <foo\+0x7> 7: R_386_PLT32 global_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp c <foo\+0xc> c: R_386_PC32 weak_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 11 <foo\+0x11> 11: R_386_PC32 weak_hidden_undef
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 16 <foo\+0x16> 16: R_386_PC32 weak_hidden_def
+[ ]*[a-f0-9]+: e9 fc ff ff ff jmp 1b <foo\+0x1b> 1b: R_386_PC32 hidden_undef
+
+0+1f <hidden_def>:
+[ ]*[a-f0-9]+: c3 ret
+
+0+20 <weak_hidden_def>:
+[ ]*[a-f0-9]+: c3 ret
+
+0+21 <global_def>:
+[ ]*[a-f0-9]+: c3 ret
+
+0+22 <weak_def>:
+[ ]*[a-f0-9]+: c3 ret
+
+0+23 <local>:
+[ ]*[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+ <foo>:
-[ ]*[a-f0-9]+: eb 1f jmp 21 <local>
-[ ]*[a-f0-9]+: eb 19 jmp 1d <hidden_def>
+[ ]*[a-f0-9]+: eb 24 jmp 26 <local>
+[ ]*[a-f0-9]+: eb 1e jmp 22 <hidden_def>
[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 9 <foo\+0x9> 5: R_X86_64_PC32 global_def-0x4
-[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq e <foo\+0xe> a: R_X86_64_PC32 weak_def-0x4
-[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 13 <foo\+0x13> f: R_X86_64_PC32 weak_hidden_undef-0x4
-[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 18 <foo\+0x18> 14: R_X86_64_PC32 weak_hidden_def-0x4
-[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1d <hidden_def> 19: R_X86_64_PC32 hidden_undef-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq e <foo\+0xe> a: R_X86_64_PLT32 global_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 13 <foo\+0x13> f: R_X86_64_PC32 weak_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 18 <foo\+0x18> 14: R_X86_64_PC32 weak_hidden_undef-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1d <foo\+0x1d> 19: R_X86_64_PC32 weak_hidden_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 22 <hidden_def> 1e: R_X86_64_PC32 hidden_undef-0x4
-0+1d <hidden_def>:
+0+22 <hidden_def>:
[ ]*[a-f0-9]+: c3 retq
-0+1e <weak_hidden_def>:
+0+23 <weak_hidden_def>:
[ ]*[a-f0-9]+: c3 retq
-0+1f <global_def>:
+0+24 <global_def>:
[ ]*[a-f0-9]+: c3 retq
-0+20 <weak_def>:
+0+25 <weak_def>:
[ ]*[a-f0-9]+: c3 retq
-0+21 <local>:
+0+26 <local>:
[ ]*[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+ <foo>:
+[ ]*[a-f0-9]+: eb 21 jmp 23 <local>
+[ ]*[a-f0-9]+: eb 1b jmp 1f <hidden_def>
+[ ]*[a-f0-9]+: eb 1b jmp 21 <global_def>
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq b <foo\+0xb> 7: R_X86_64_PLT32 global_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 10 <foo\+0x10> c: R_X86_64_PC32 weak_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 15 <foo\+0x15> 11: R_X86_64_PC32 weak_hidden_undef-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1a <foo\+0x1a> 16: R_X86_64_PC32 weak_hidden_def-0x4
+[ ]*[a-f0-9]+: e9 00 00 00 00 jmpq 1f <hidden_def> 1b: R_X86_64_PC32 hidden_undef-0x4
+
+0+1f <hidden_def>:
+[ ]*[a-f0-9]+: c3 retq
+
+0+20 <weak_hidden_def>:
+[ ]*[a-f0-9]+: c3 retq
+
+0+21 <global_def>:
+[ ]*[a-f0-9]+: c3 retq
+
+0+22 <weak_def>:
+[ ]*[a-f0-9]+: c3 retq
+
+0+23 <local>:
+[ ]*[a-f0-9]+: c3 retq
+#pass
--
2.1.0