linux/arch/loongarch
Linus Torvalds 4356e9f841 work around gcc bugs with 'asm goto' with outputs
We've had issues with gcc and 'asm goto' before, and we created a
'asm_volatile_goto()' macro for that in the past: see commits
3f0116c323 ("compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug") and a9f180345f ("compiler/gcc4: Make quirk for
asm_volatile_goto() unconditional").

Then, much later, we ended up removing the workaround in commit
43c249ea0b ("compiler-gcc.h: remove ancient workaround for gcc PR
58670") because we no longer supported building the kernel with the
affected gcc versions, but we left the macro uses around.

Now, Sean Christopherson reports a new version of a very similar
problem, which is fixed by re-applying that ancient workaround.  But the
problem in question is limited to only the 'asm goto with outputs'
cases, so instead of re-introducing the old workaround as-is, let's
rename and limit the workaround to just that much less common case.

It looks like there are at least two separate issues that all hit in
this area:

 (a) some versions of gcc don't mark the asm goto as 'volatile' when it
     has outputs:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619
        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420

     which is easy to work around by just adding the 'volatile' by hand.

 (b) Internal compiler errors:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422

     which are worked around by adding the extra empty 'asm' as a
     barrier, as in the original workaround.

but the problem Sean sees may be a third thing since it involves bad
code generation (not an ICE) even with the manually added 'volatile'.

but the same old workaround works for this case, even if this feels a
bit like voodoo programming and may only be hiding the issue.

Reported-and-tested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Andrew Pinski <quic_apinski@quicinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-02-09 15:57:48 -08:00
..
boot LoongArch: dts: DeviceTree for Loongson-2K2000 2024-01-17 12:43:08 +08:00
configs LoongArch changes for v6.8 2024-01-19 13:30:49 -08:00
crypto crypto: loongarch/crc32 - remove redundant setting of alignmask to 0 2023-10-27 18:04:24 +08:00
include work around gcc bugs with 'asm goto' with outputs 2024-02-09 15:57:48 -08:00
kernel LoongArch: Change acpi_core_pic[NR_CPUS] to acpi_core_pic[MAX_CORE_PIC] 2024-02-06 12:32:05 +08:00
kvm LoongArch: KVM: Fix build due to API changes 2024-01-26 16:22:07 +08:00
lib LoongArch: Add KASAN (Kernel Address Sanitizer) support 2023-09-06 22:54:16 +08:00
mm LoongArch: Fix earlycon parameter if KASAN enabled 2024-02-06 12:32:05 +08:00
net LoongArch: BPF: Prevent out-of-bounds memory access 2024-01-17 12:43:13 +08:00
pci LoongArch: Add FDT booting support from efi system table 2022-12-14 08:41:53 +08:00
power LoongArch: Export some arch-specific pm interfaces 2023-06-29 20:58:44 +08:00
vdso LoongArch: vDSO: Disable UBSAN instrumentation 2024-02-06 12:32:05 +08:00
Kbuild LoongArch: Allow device trees be built into the kernel 2024-01-17 12:43:00 +08:00
Kconfig LoongArch: Select HAVE_ARCH_SECCOMP to use the common SECCOMP menu 2024-02-06 12:32:05 +08:00
Kconfig.debug LoongArch: Add prologue unwinder support 2022-08-12 13:10:11 +08:00
Makefile LoongArch: Allow device trees be built into the kernel 2024-01-17 12:43:00 +08:00