Re: [PATCH] BaseTools/tools_def: add "-fno-unwind-tables" to GCC_AARCH64_CC_FLAGS

[Laszlo Ersek <lersek@redhat.com>]

On 05/21/18 11:32, Ard Biesheuvel wrote:
> On 21 May 2018 at 02:37, Gao, Liming <liming.gao@intel.com> wrote:
>> Laszlo:
>>   Is this change required for IA32 and X64 arch?
>>
> 
> The upstream GCC change is limited to AArch64, but I suppose it
> wouldn't hurt to add this to IA32/X64 as well, given that it currently
> only reaffirms the default, and will do the right thing if that
> default ever changes for IA32/X64 as well.

Right; I wanted to keep the patch surgical. I don't really understand
why it makes sense for gcc to use different "unwind-tables" defaults for
AARCH64 vs. IA32/X64; however, I did think the gcc developers must have
made a conscious decision, to restrict the change to AARCH64.

I can submit a followup patch for IA32/X64, but I'll first respond under
Leif's suggestion too (that subthread will likely take more discussion).

Thanks!
Laszlo

> 
> 
>>> -----Original Message-----
>>> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>>> Sent: Saturday, May 19, 2018 4:21 PM
>>> To: Laszlo Ersek <lersek@redhat.com>
>>> Cc: edk2-devel-01 <edk2-devel@lists.01.org>; Danilo C. L. de Paula <ddepaula@redhat.com>; Cole Robinson <crobinso@redhat.com>;
>>> Gerd Hoffmann <kraxel@redhat.com>; Leif Lindholm <leif.lindholm@linaro.org>; Gao, Liming <liming.gao@intel.com>; Paolo Bonzini
>>> <pbonzini@redhat.com>; Zhu, Yonghong <yonghong.zhu@intel.com>
>>> Subject: Re: [PATCH] BaseTools/tools_def: add "-fno-unwind-tables" to GCC_AARCH64_CC_FLAGS
>>>
>>> On 18 May 2018 at 20:23, Laszlo Ersek <lersek@redhat.com> wrote:
>>>> The ElfConvert routines in GenFw don't handle the ".eh_frame" ELF section
>>>> emitted by gcc. For this reason, Leif disabled the generation of that
>>>> section for AARCH64 with "-fno-asynchronous-unwind-tables" in commit
>>>> 28e80befa4fe [1], and Ard did the same for IA32 and X64 in commit
>>>> 26ecc55c027d [2]. (The CLANG38 toolchain received the same flag at its
>>>> inception, in commit 6f756db5ea05 [3].)
>>>>
>>>> However, ".eh_frame" is back now; in upstream gcc commit 9cbee213b579 [4]
>>>> (part of tag "gcc-8_1_0-release"), both "-fasynchronous-unwind-tables" and
>>>> "-funwind-tables" were made the default for AARCH64. (The patch author
>>>> described the effects on the gcc mailing list [5].) We have to counter the
>>>> latter flag with "-fno-unwind-tables", otherwise GenFw chokes on
>>>> ".eh_frame" again (triggered for example on Fedora 28).
>>>>
>>>> "-f[no-]unwind-tables" goes back to at least gcc-4.4 [6], so it's safe to
>>>> add to GCC_AARCH64_CC_FLAGS.
>>>>
>>>> [1] https://github.com/tianocore/edk2/commit/28e80befa4fe
>>>> [2] https://github.com/tianocore/edk2/commit/26ecc55c027d
>>>> [3] https://github.com/tianocore/edk2/commit/6f756db5ea05
>>>> [4] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=9cbee213b579
>>>> [5] http://mid.mail-archive.com/7b28c03a-c032-6cec-c127-1c12cbe98eeb@foss.arm.com
>>>> [6] https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Code-Gen-Options.html
>>>>
>>>> Cc: "Danilo C. L. de Paula" <ddepaula@redhat.com>
>>>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>>> Cc: Cole Robinson <crobinso@redhat.com>
>>>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>>>> Cc: Leif Lindholm <leif.lindholm@linaro.org>
>>>> Cc: Liming Gao <liming.gao@intel.com>
>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>> Cc: Yonghong Zhu <yonghong.zhu@intel.com>
>>>> Reported-by: "Danilo C. L. de Paula" <ddepaula@redhat.com>
>>>> Contributed-under: TianoCore Contribution Agreement 1.1
>>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>>
>>> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>>
>>>> ---
>>>>
>>>> Notes:
>>>>     Repo:   https://github.com/lersek/edk2.git
>>>>     Branch: aarch64_no_unwind_tables
>>>>
>>>>  BaseTools/Conf/tools_def.template | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
>>>> index 03d700018550..9429033fe2e3 100755
>>>> --- a/BaseTools/Conf/tools_def.template
>>>> +++ b/BaseTools/Conf/tools_def.template
>>>> @@ -4537,7 +4537,7 @@ DEFINE GCC_X64_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mno-red-zone -Wno-ad
>>>>  DEFINE GCC_IPF_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -minline-int-divide-min-latency
>>>>  DEFINE GCC_ARM_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -mabi=aapcs -fno-short-enums
>>> -funsigned-char -ffunction-sections -fdata-sections -fomit-frame-pointer -Wno-address -mthumb -mfloat-abi=soft -fno-pic -fno-pie
>>>>  DEFINE GCC_ARM_CC_XIPFLAGS         = -mno-unaligned-access
>>>> -DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm
>>> -funsigned-char  -ffunction-sections -fdata-sections -Wno-address -fno-asynchronous-unwind-tables -fno-pic -fno-pie -ffixed-x18
>>>> +DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm
>>> -funsigned-char  -ffunction-sections -fdata-sections -Wno-address -fno-asynchronous-unwind-tables -fno-unwind-tables -fno-pic
>>> -fno-pie -ffixed-x18
>>>>  DEFINE GCC_AARCH64_CC_XIPFLAGS     = -mstrict-align -mgeneral-regs-only
>>>>  DEFINE GCC_DLINK_FLAGS_COMMON      = -nostdlib --pie
>>>>  DEFINE GCC_DLINK2_FLAGS_COMMON     = -Wl,--script=$(EDK_TOOLS_PATH)/Scripts/GccBase.lds
>>>> --
>>>> 2.14.1.3.gb7cf6e02401b
>>>>