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

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

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.


>> -----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
>> >