Messages in this thread | | | Date | Wed, 06 Mar 2019 08:58:43 +0100 | From | Stefan Agner <> | Subject | Re: [PATCH 1/2] ARM: drop unnecessary WASM |
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On 06.03.2019 00:39, Robin Murphy wrote: > Hi Stefan, > > On 2019-03-05 10:18 pm, Stefan Agner wrote: >> The W macro for generating wide instructions when targeting Thumb-2 >> is not required for the preload data instructions (pld, pldw) since >> they are only available as wide instructions. The GNU assembler seems >> to work with or without the .w appended when compiling an Thumb-2 >> kernel. However, Clang's integrated assembler does not consider the >> .w variants as valid instructions: >> >> ./arch/arm/include/asm/processor.h:133:5: error: invalid instruction >> "pldw.w\t%a0 \n" >> ^ >> <inline asm>:2:1: note: instantiated into assembly here >> pldw.w [r0] >> ^ >> 1 error generated. > > Have you filed a bug against Clang for that? Something like "pldwal.w" > may be super-redundant, but it's still perfectly valid syntax. The > "Standard assembler syntax fields" section of the Arm ARM even calls > out that "...the .W qualifier has no effect" on ARM/A32 instructions > since they are inherently 32-bit; that should equally apply for 32-bit > only Thumb/T32 instructions. There are certainly a few instructions > which don't allow a condition code (even "AL"), but off-hand I don't > remember any not having the optional {<q>} field in their syntax.
Good point, bug filed: https://bugs.llvm.org/show_bug.cgi?id=40972
Will send a v2 and note that this is a work around for Clang and reference the bug.
-- Stefan
> > That said, obviously the patch itself is no problem since the syntax > *is* redundant here, but it really is just a workaround for an > assembler bug. > > Robin. > >> Drop the macro to make sure non-wide variants of pld and pldw are >> emitted in all cases. >> >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> arch/arm/include/asm/processor.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h >> index 120f4c9bbfde..042d77cf686d 100644 >> --- a/arch/arm/include/asm/processor.h >> +++ b/arch/arm/include/asm/processor.h >> @@ -131,8 +131,8 @@ static inline void prefetchw(const void *ptr) >> __asm__ __volatile__( >> ".arch_extension mp\n" >> __ALT_SMP_ASM( >> - WASM(pldw) "\t%a0", >> - WASM(pld) "\t%a0" >> + "pldw\t%a0", >> + "pld\t%a0" >> ) >> :: "p" (ptr)); >> } >>
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