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Turn on -fomit-frame-pointer by default for 32bit x86?

Message ID AANLkTimEjx_mMsUWM2niDdmdefVLbAgksSVJLsl23_es@mail.gmail.com
State New
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Commit Message

H.J. Lu July 14, 2010, 9:55 p.m. UTC 
On Wed, Jul 14, 2010 at 6:46 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Jul 14, 2010 at 1:09 AM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
>> On Tue, Jul 13, 2010 at 11:44 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Tue, Jul 13, 2010 at 2:02 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>>> On Tue, Jul 13, 2010 at 2:01 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>>>> On Tue, Jul 13, 2010 at 1:59 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>> What will stop working when -fomit-frame-pointer is on?
>>>>>
>>>>> backtraces when debugging information is not turned on.
>>>>
>>>> See http://gcc.gnu.org/ml/gcc-patches/2004-08/msg01033.html and many
>>>> more.  This is not the first time this has been discussed.
>>>
>>> Most of 32bit x86 assembly codes in glibc have .eh_frame section.
>>> If backtrace is absolutely needed, they can add -fasynchronous-unwind-tables
>>> or -fno-omit-frame-pointer.
>>
>> We build opensuse with -fomit-frame-pointer -fasynchronous-unwind-tables.
>> If you want to make -fomit-frame-pointer the default then you should enable
>> unwind tables by default.
>>
>
> I will try and make it target/OS dependent.
>

Here is a patch. How does it look?
diff mbox

Patch

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 4fd2aab..fe30bfd 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2985,10 +2985,23 @@  override_options (bool main_args_p)
     {
       if (flag_zee == 2)
         flag_zee = 0;
+      /* Unwind info is not correct around the CFG unless either a
+	 frame pointer is present or -maccumulate-outgoing-args is
+	 set. When both -fasynchronous-unwind-tables and
+	 -fomit-frame-pointer are turned on by default, turn off
+	 both if -mno-accumulate-outgoing-args is used.  */
       if (flag_omit_frame_pointer == 2)
-	flag_omit_frame_pointer = 0;
+	flag_omit_frame_pointer
+	  = (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+	     && (!TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+		 || !(target_flags_explicit
+		      & MASK_ACCUMULATE_OUTGOING_ARGS)));
       if (flag_asynchronous_unwind_tables == 2)
-	flag_asynchronous_unwind_tables = 0;
+	flag_asynchronous_unwind_tables
+	  = (TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+	     && (!TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+		 || !(target_flags_explicit
+		      & MASK_ACCUMULATE_OUTGOING_ARGS)));
       if (flag_pcc_struct_return == 2)
 	flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;
     }
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index eb3eb9f..c0ae95f 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -467,6 +467,8 @@  extern tree x86_mfence;
 /* Extra bits to force on w/ 32-bit mode.  */
 #define TARGET_SUBTARGET32_DEFAULT 0
 #define TARGET_SUBTARGET32_ISA_DEFAULT 0
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 0
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 0

 /* Extra bits to force on w/ 64-bit mode.  */
 #define TARGET_SUBTARGET64_DEFAULT 0
diff --git a/gcc/config/i386/linux.h b/gcc/config/i386/linux.h
index 81dfd1e..61d53b5 100644
--- a/gcc/config/i386/linux.h
+++ b/gcc/config/i386/linux.h
@@ -219,3 +219,10 @@  along with GCC; see the file COPYING3.  If not see
 /* i386 glibc provides __stack_chk_guard in %gs:0x14.  */
 #define TARGET_THREAD_SSP_OFFSET	0x14
 #endif
+
+/* Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables by
+   default.  */
+#undef TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 1
+#undef TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 1
diff --git a/gcc/config/i386/linux64.h b/gcc/config/i386/linux64.h
index 33b4dc9..5a02205 100644
--- a/gcc/config/i386/linux64.h
+++ b/gcc/config/i386/linux64.h
@@ -123,3 +123,10 @@  see the files COPYING3 and COPYING.RUNTIME
respectively.  If not, see
    x86_64 glibc provides it in %fs:0x28.  */
 #define TARGET_THREAD_SSP_OFFSET	(TARGET_64BIT ? 0x28 : 0x14)
 #endif
+
+/* Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables by
+   default.  */
+#undef TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 1
+#undef TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT