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Re: Turn on -fomit-frame-pointer by default for 32bit x86?
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?
--
H.J.
--
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
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 1