On 21 June 2017 at 02:11, Gao, Liming <liming....@intel.com> wrote: > Reviewed-by: Liming Gao <liming....@intel.com> >
Thanks, pushed as 9ba8baae15ca >>-----Original Message----- >>From: Leif Lindholm [mailto:leif.lindh...@linaro.org] >>Sent: Wednesday, June 21, 2017 4:00 AM >>To: Ard Biesheuvel <ard.biesheu...@linaro.org> >>Cc: edk2-devel@lists.01.org; Gao, Liming <liming....@intel.com>; Zhu, >>Yonghong <yonghong....@intel.com>; ler...@redhat.com >>Subject: Re: [PATCH 2/2] BaseTools/tools_def: AARCH64: disable LTO type >>mismatch warnings >> >>On Tue, Jun 20, 2017 at 08:43:54PM +0200, Ard Biesheuvel wrote: >>> On AARCH64, any code that may execute with the MMU off needs to be >>built >>> with -mstrict-align, given that unaligned accesses are not allowed unless >>> the MMU is enabled. This does not only affect SEC and PEI modules, but >>> also static libraries of the BASE type, which may be linked into such >>> modules, as well as into modules of other types. As it turns out, the >>> presence of -mstrict-align is reflected in the internal representations >>> of the types defined in those libraries. >>> >>> When -fstrict-aliasing is passed to GCC, it assumes that pointers to >>> objects of different types cannot refer to the same memory location, and >>> attempts to exploit this fact when optimizing the code. Since such >>> assumptions are only valid under very strict conditions which are not >>> guaranteed to be met in EDK2, we disable this optimization by passing >>> -fno-strict-aliasing by default. >> >>Just a comment - you don't necessarily have to update this excellent >>commit mesage, but: >>-fstrict-aliasing is GCC default, because it is a restriction in the C >>language. Because it's a bit non-obvious, things can go hilariously >>wrong in very non-obvious ways, and the potential optimization gains >>are ulikely to be generally relevant, -fno-strict-aliasing is a >>sensible thing to always have set (like we do). >> >>> When LTO is in effect, this applies equally to the code generation that >>> may occur at link time, which is why the linker warns about unexpected >>> differences in type definitions between the intermediate representations >>> that are present in the object files being linked. This may result in >>> warnings such as the one below, even if -fno-strict-aliasing is used: >>> >>> MdePkg/Include/Library/BaseLib.h:1712:1: >>> warning: type of 'StrToGuid' does not match original declaration >>> [-Wlto-type-mismatch] >>> StrToGuid ( >>> ^ >>> MdePkg/Library/BaseLib/SafeString.c:1506:1: >>> note: 'StrToGuid' was previously declared here >>> StrToGuid ( >>> ^ >>> MdePkg/Library/BaseLib/SafeString.c:1506:1: >>> note: code may be misoptimized unless -fno-strict-aliasing is used >>> >>> This warning is inadvertently triggered when linking BASE libraries built >>> with -mstrict-align into modules of types other than SEC or PEI, since the >>> types are subtly different, even though the use of code that maintains >>> strict alignment in a module that does not care about this is unlikely to >>> cause problems. And even if it did, it would still only affect code built >>> with -fstrict-aliasing enabled, which we disable unconditionally. So let's >>> just silence the warning by passing -Wno-lto-type-mismatch. >>> >>> Contributed-under: TianoCore Contribution Agreement 1.0 >>> Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org> >> >>Reviewed-by: Leif Lindholm <leif.lindh...@linaro.org> >> >>> --- >>> 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 7a58ce365ed2..9a3ba9defb12 100755 >>> --- a/BaseTools/Conf/tools_def.template >>> +++ b/BaseTools/Conf/tools_def.template >>> @@ -5407,7 +5407,7 @@ RELEASE_GCC5_ARM_DLINK_FLAGS = >>DEF(GCC5_ARM_DLINK_FLAGS) -flto -Os -L$(WORKS >>> DEBUG_GCC5_AARCH64_DLINK_XIPFLAGS = -z common-page-size=0x20 >>> >>> RELEASE_GCC5_AARCH64_CC_FLAGS = DEF(GCC5_AARCH64_CC_FLAGS) - >>flto -Wno-unused-but-set-variable -mcmodel=tiny -fomit-frame-pointer >>> -RELEASE_GCC5_AARCH64_DLINK_FLAGS = >>DEF(GCC5_AARCH64_DLINK_FLAGS) -flto -Os - >>L$(WORKSPACE)/ArmPkg/Library/GccLto -llto-aarch64 -Wl,-plugin-opt=-pass- >>through=-llto-aarch64 >>> +RELEASE_GCC5_AARCH64_DLINK_FLAGS = >>DEF(GCC5_AARCH64_DLINK_FLAGS) -flto -Os - >>L$(WORKSPACE)/ArmPkg/Library/GccLto -llto-aarch64 -Wl,-plugin-opt=-pass- >>through=-llto-aarch64 -Wno-lto-type-mismatch >>> >>> NOOPT_GCC5_AARCH64_CC_FLAGS = DEF(GCC5_AARCH64_CC_FLAGS) - >>O0 -mcmodel=small >>> NOOPT_GCC5_AARCH64_DLINK_FLAGS = >>DEF(GCC5_AARCH64_DLINK_FLAGS) -z common-page-size=0x1000 -O0 >>> -- >>> 2.7.4 >>> _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
