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From: "Ard Biesheuvel" <ardb@kernel.org>
Date: Tue, 13 Apr 2021 18:36:31 +0200
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Subject: Re: [edk2-devel] GCC49 DEBUG AARCH64 and ARM builds use -O0
To: Rebecca Cran <rebecca@nuviainc.com>
Cc: Laszlo Ersek <lersek@redhat.com>, edk2-devel-groups-io <devel@edk2.groups.io>, 
	Leif Lindholm <leif@nuviainc.com>, 
	"Liming Gao (Byosoft address)" <gaoliming@byosoft.com.cn>, Ard Biesheuvel <ardb+tianocore@kernel.org>
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On Tue, 13 Apr 2021 at 14:12, Rebecca Cran <rebecca@nuviainc.com> wrote:
>
> +Ard (with the correct email address)
>
> On 4/13/21 4:32 AM, Laszlo Ersek wrote:
> > +Liming
> >
> > On 04/12/21 17:10, Rebecca Cran wrote:
> >> I noticed the GCC49 (and GCC48) AARCH64 and ARM DEBUG builds use -O0,
> >> unlike IA32 and X64 platforms which build with -Os.
> >>
> >> e.g. from
> >> https://github.com/tianocore/edk2/blob/master/BaseTools/Conf/tools_def.template
> >> :
> >>
> >> DEBUG_GCC49_AARCH64_CC_FLAGS     = DEF(GCC49_AARCH64_CC_FLAGS) -O0
> >>
> >> Is that deliberate, or should it be like X64 where DEBUG builds are
> >> optimized and NOOPT is used when unoptimized binaries are needed?
> >>
> >
> > Seems to go back to commit dafe0fedc508 ("BaseTools: Add GCC49
> > toolchain; align data sections to 0x40", 2014-07-28). My guess is that
> > in 2014, gcc (4.9) may have had issues with arm64 code generation with -Os.
> >
> > You hint at DEBUG_GCC48_AARCH64_CC_FLAGS too, which seems like a
> > promising clue at first -- because, perhaps the GCC49 flags in the
> > above-mentioned commit had simply been modeled on the then-existent
> > GCC48 ones.
> >
> > Unfortunately however, the GCC48 entry appeared in the
> > less-than-helpfully-explained commit 2bc3256ca6d4 ("Sync BaseTool trunk
> > (version r2640) into EDKII BaseTools.", 2014-01-10).
> >
> > Thanks
> > Laszlo
> >
>

IIRC we only added NOOPT for ARM much later, and at that time, we
decided to leave GCC49 alone.