Messages in this thread | | | Date | Fri, 5 Nov 2021 09:04:00 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 21/22] x86,word-at-a-time: Remove .fixup usage |
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On Thu, Nov 04, 2021 at 04:33:10PM -0700, Josh Poimboeuf wrote: > On Thu, Nov 04, 2021 at 05:47:50PM +0100, Peter Zijlstra wrote: > > XXX: I'm not really happy with this patch > > > > static inline unsigned long load_unaligned_zeropad(const void *addr) > > { > > - unsigned long ret, dummy; > > + unsigned long ret; > > + > > + asm("1:\tmov (%0),%0\n" > > + "2:\n" > > + _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_LOAD_UNALIGNED, %0) > > + : "=&r" (ret) > > + : "0" ((unsigned long)addr)); > > > > - asm( > > - "1:\tmov %2,%0\n" > > - "2:\n" > > - ".section .fixup,\"ax\"\n" > > - "3:\t" > > - "lea %2,%1\n\t" > > - "and %3,%1\n\t" > > - "mov (%1),%0\n\t" > > - "leal %2,%%ecx\n\t" > > - "andl %4,%%ecx\n\t" > > - "shll $3,%%ecx\n\t" > > - "shr %%cl,%0\n\t" > > - "jmp 2b\n" > > - ".previous\n" > > - _ASM_EXTABLE(1b, 3b) > > - :"=&r" (ret),"=&c" (dummy) > > - :"m" (*(unsigned long *)addr), > > - "i" (-sizeof(unsigned long)), > > - "i" (sizeof(unsigned long)-1)); > > return ret; > > } > > Yeah, it hurts code generation and I guess it's a hot path. > > Maybe put the fixup code in the function. In case of > CONFIG_CC_HAS_ASM_GOTO_OUTPUT, it could be at a label at the end of the > function. Otherwise it'd have to be inline.
Ooh, yes. If we use ASM_GOTO_OUTPUT then it'll work just right, and the legacy code will get worse, but I can live with that (everybody is already building their kernels with gcc-11/clang anyway :-))
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