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Re: PATCH] PR target/65612: Multiversioning doesn't work with DSO nor PIE



On 09/05/15 19:57, Szabolcs Nagy wrote:
> * H.J. Lu <hjl.tools@gmail.com> [2015-05-09 10:41:41 -0700]:
>> There are
>>
>>      4: 0000000000002b70   806 FUNC    GLOBAL DEFAULT   12
>> __cpu_indicator_init@GCC_4.8.0
>>     38: 00000000002153d0    16 OBJECT  GLOBAL DEFAULT   25 __cpu_model@GCC_4.8.0
>>
>> and
>>
>> 000000000215000  0000000400000001 R_X86_64_64
>> 0000000000002b70 __cpu_indicator_init@GCC_4.8.0 + 0
>> 0000000000215220  0000002600000006 R_X86_64_GLOB_DAT
>> 00000000002153d0 __cpu_model@GCC_4.8.0 + 0
>>
>> in libgcc_s.so.1.  Musl ld.so must be fixed to handle it.
>>

Rich is looking at how to do this non-intrusively, but
it seems non-trivial (some users of musl prefer not to
resolve such versioned symbols).

> 
> i think it might be enough to add __cpu_indicator_init_local
> as an alias to __cpu_indicator_init in libgcc.a and then use
> the *_local symbol from the ifunc resolver, that way no new
> dependency is added to libgcc_s.so handling.

i tried this approach and it seems to work: passes all
multiversioning tests on x86_64.

i think it's no worse than the symver approach.

is it ok to change the current fix to this?


libgcc/Changelog:

2015-05-11  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* config/i386/cpuinfo.c (__cpu_indicator_init_local): Add.
	(__cpu_indicator_init@GCC_4.8.0, __cpu_model@GCC_4.8.0): Remove.

	* config/i386/t-linux (HOST_LIBGCC2_CFLAGS): Remove -DUSE_ELF_SYMVER.

gcc/Changelog:

2015-05-11  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* config/i386/i386.c (ix86_expand_builtin): Make __builtin_cpu_init
	call __cpu_indicator_init_local instead of __cpu_indicator_init.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 7bd9ff3..7327cf3 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -38398,10 +38398,10 @@ ix86_expand_builtin (tree exp, rtx target, rtx subtarget,
     {
     case IX86_BUILTIN_CPU_INIT:
       {
-	/* Make it call __cpu_indicator_init in libgcc. */
+	/* Make it call __cpu_indicator_init_local in libgcc.a. */
 	tree call_expr, fndecl, type;
         type = build_function_type_list (integer_type_node, NULL_TREE); 
-	fndecl = build_fn_decl ("__cpu_indicator_init", type);
+	fndecl = build_fn_decl ("__cpu_indicator_init_local", type);
 	call_expr = build_call_expr (fndecl, 0); 
 	return expand_expr (call_expr, target, mode, EXPAND_NORMAL);
       }
diff --git a/libgcc/config/i386/cpuinfo.c b/libgcc/config/i386/cpuinfo.c
index f6f91dd..86b6d21 100644
--- a/libgcc/config/i386/cpuinfo.c
+++ b/libgcc/config/i386/cpuinfo.c
@@ -425,7 +425,7 @@ __cpu_indicator_init (void)
   return 0;
 }
 
-#if defined SHARED && defined USE_ELF_SYMVER
-__asm__ (".symver __cpu_indicator_init, __cpu_indicator_init@GCC_4.8.0");
-__asm__ (".symver __cpu_model, __cpu_model@GCC_4.8.0");
+#ifndef SHARED
+int __cpu_indicator_init_local (void)
+  __attribute__ ((weak, alias ("__cpu_indicator_init")));
 #endif
diff --git a/libgcc/config/i386/t-linux b/libgcc/config/i386/t-linux
index 11bb46e..4f47f7b 100644
--- a/libgcc/config/i386/t-linux
+++ b/libgcc/config/i386/t-linux
@@ -3,4 +3,4 @@
 # t-slibgcc-elf-ver and t-linux
 SHLIB_MAPFILES = libgcc-std.ver $(srcdir)/config/i386/libgcc-glibc.ver
 
-HOST_LIBGCC2_CFLAGS += -mlong-double-80 -DUSE_ELF_SYMVER
+HOST_LIBGCC2_CFLAGS += -mlong-double-80

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