| Message ID | 20230318041555.4192172-1-davidgow@google.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | arch:um: Only disable SSE on clang to work around old GCC bugs | expand |
> As part of the Rust support for UML, we disable SSE (and similar flags) > to match the normal x86 builds. This both makes sense (we ideally want a > similar configuration to x86), and works around a crash bug with SSE > generation under Rust with LLVM. > > However, this breaks compiling stdlib.h under gcc < 11, as the x86_64 > ABI requires floating-point return values be stored in an SSE register. > gcc 11 fixes this by only doing register allocation when a function is > actually used, and since we never use atof(), it shouldn't be a problem: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 > > Nevertheless, only disable SSE on clang setups, as that's a simple way > of working around everyone's bugs. > > Fixes: 884981867947 ("rust: arch/um: Disable FP/SIMD instruction to match x86") > Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/ > Tested-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Tested-by: SeongJae Park <sj@kernel.org> > Signed-off-by: David Gow <davidgow@google.com> > --- > arch/x86/Makefile.um | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um > index b70559b821df..2106a2bd152b 100644 > --- a/arch/x86/Makefile.um > +++ b/arch/x86/Makefile.um > @@ -3,9 +3,14 @@ core-y += arch/x86/crypto/ > > # > # Disable SSE and other FP/SIMD instructions to match normal x86 > +# This is required to work around issues in older LLVM versions, but breaks > +# GCC versions < 11. See: > +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 > # > +ifeq ($(CONFIG_CC_IS_CLANG),y) > KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx > KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 > +endif > > ifeq ($(CONFIG_X86_32),y) > START := 0x8048000 > -- > 2.40.0.rc1.284.g88254d51c5-goog Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
On 18/03/23 01:15, 'David Gow' via KUnit Development wrote: > As part of the Rust support for UML, we disable SSE (and similar flags) > to match the normal x86 builds. This both makes sense (we ideally want a > similar configuration to x86), and works around a crash bug with SSE > generation under Rust with LLVM. > > However, this breaks compiling stdlib.h under gcc < 11, as the x86_64 > ABI requires floating-point return values be stored in an SSE register. > gcc 11 fixes this by only doing register allocation when a function is > actually used, and since we never use atof(), it shouldn't be a problem: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 > > Nevertheless, only disable SSE on clang setups, as that's a simple way > of working around everyone's bugs. > > Fixes: 884981867947 ("rust: arch/um: Disable FP/SIMD instruction to match x86") > Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/ > Tested-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Tested-by: SeongJae Park <sj@kernel.org> > Signed-off-by: David Gow <davidgow@google.com> > --- > arch/x86/Makefile.um | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um > index b70559b821df..2106a2bd152b 100644 > --- a/arch/x86/Makefile.um > +++ b/arch/x86/Makefile.um > @@ -3,9 +3,14 @@ core-y += arch/x86/crypto/ > > # > # Disable SSE and other FP/SIMD instructions to match normal x86 > +# This is required to work around issues in older LLVM versions, but breaks > +# GCC versions < 11. See: > +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 > # > +ifeq ($(CONFIG_CC_IS_CLANG),y) > KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx > KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 > +endif > > ifeq ($(CONFIG_X86_32),y) > START := 0x8048000 Tested-by: Arthur Grillo <arthurgrillo@riseup.net>
On Sat, 18 Mar 2023 at 12:16, David Gow <davidgow@google.com> wrote: > > As part of the Rust support for UML, we disable SSE (and similar flags) > to match the normal x86 builds. This both makes sense (we ideally want a > similar configuration to x86), and works around a crash bug with SSE > generation under Rust with LLVM. > > However, this breaks compiling stdlib.h under gcc < 11, as the x86_64 > ABI requires floating-point return values be stored in an SSE register. > gcc 11 fixes this by only doing register allocation when a function is > actually used, and since we never use atof(), it shouldn't be a problem: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 > > Nevertheless, only disable SSE on clang setups, as that's a simple way > of working around everyone's bugs. > > Fixes: 884981867947 ("rust: arch/um: Disable FP/SIMD instruction to match x86") > Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/ > Tested-by: Roberto Sassu <roberto.sassu@huaweicloud.com> > Tested-by: SeongJae Park <sj@kernel.org> > Signed-off-by: David Gow <davidgow@google.com> > --- Any chance we could get this picked up as a fix for 6.3? The UML build is still broken with older gcc versions. Cheers, -- David
----- Ursprüngliche Mail ----- > Von: "davidgow" <davidgow@google.com> > An: "richard" <richard@nod.at>, "anton ivanov" <anton.ivanov@cambridgegreys.com>, "Johannes Berg" > Any chance we could get this picked up as a fix for 6.3? The UML build > is still broken with older gcc versions. Sure. Just got flooded with other stuff. :-S Thanks, //richard
On Sat, Mar 18, 2023 at 5:16 AM David Gow <davidgow@google.com> wrote: > > Nevertheless, only disable SSE on clang setups, as that's a simple way > of working around everyone's bugs. Sounds good to me. If GCC >= 11 has fixed it, should we instead test for GCC < 11, i.e. it could help catching future new regressions like the linked GCC bug, if I understand correctly, right? Of course, that could be done for the next cycle, since this one minimizes the original change w.r.t. v6.2. By the way, missing space on the title (`arch:um`). Cheers, Miguel
----- Ursprüngliche Mail ----- >> Von: "davidgow" <davidgow@google.com> >> An: "richard" <richard@nod.at>, "anton ivanov" >> <anton.ivanov@cambridgegreys.com>, "Johannes Berg" >> Any chance we could get this picked up as a fix for 6.3? The UML build >> is still broken with older gcc versions. > > Sure. Just got flooded with other stuff. :-S Patch applied to fixes branch. PR will happen soon. Thanks everyone and sorry for the delay on my side! -- Thanks, //richard
diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um index b70559b821df..2106a2bd152b 100644 --- a/arch/x86/Makefile.um +++ b/arch/x86/Makefile.um @@ -3,9 +3,14 @@ core-y += arch/x86/crypto/ # # Disable SSE and other FP/SIMD instructions to match normal x86 +# This is required to work around issues in older LLVM versions, but breaks +# GCC versions < 11. See: +# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 # +ifeq ($(CONFIG_CC_IS_CLANG),y) KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 +endif ifeq ($(CONFIG_X86_32),y) START := 0x8048000
As part of the Rust support for UML, we disable SSE (and similar flags) to match the normal x86 builds. This both makes sense (we ideally want a similar configuration to x86), and works around a crash bug with SSE generation under Rust with LLVM. However, this breaks compiling stdlib.h under gcc < 11, as the x86_64 ABI requires floating-point return values be stored in an SSE register. gcc 11 fixes this by only doing register allocation when a function is actually used, and since we never use atof(), it shouldn't be a problem: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652 Nevertheless, only disable SSE on clang setups, as that's a simple way of working around everyone's bugs. Fixes: 884981867947 ("rust: arch/um: Disable FP/SIMD instruction to match x86") Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com> Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/ Tested-by: Roberto Sassu <roberto.sassu@huaweicloud.com> Tested-by: SeongJae Park <sj@kernel.org> Signed-off-by: David Gow <davidgow@google.com> --- arch/x86/Makefile.um | 5 +++++ 1 file changed, 5 insertions(+)