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

[Leif Lindholm <leif.lindholm@linaro.org>]

On Fri, May 18, 2018 at 08:23:01PM +0200, Laszlo Ersek 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.

I'm not against this patch (which fixes a real problem), but would
it be possible to take the opposite approach, as Peter Jones did for
GRUB when the same issue hit there?:

http://lists.gnu.org/archive/html/grub-devel/2018-02/msg00095.html

I.e., rather than keep adding flags when new "special" sections are
added by toolchains, explicitly filter those out as part of the link
step.

/
    Leif

> [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>
> ---
> 
> 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
>