| Date | Sun, 19 Aug 2012 09:37:27 +0100 | From | "Jan Beulich" <> | Subject | Re: [PATCH 48/74] x86, lto: Use inline assembler instead of global register variable to get sp |
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>>> Andi Kleen <andi@firstfloor.org> 08/19/12 4:59 AM >>> >I verified this generates the same binary (on 64bit) as the original >register variable.
This isn't very surprising given that the modified code is inside a CONFIG_X86_32 conditional (as ought to be obvious from the code using %%esp). Given that it's being used as operand to a binary &, the resulting code - if the compiler handles this only half way sensibly - can hardly be expected to be identical.
>-register unsigned long current_stack_pointer asm("esp") __used; >+#define current_stack_pointer ({ \ >+ unsigned long sp; \ >+ asm("mov %%esp,%0" : "=r" (sp)); \ >+ sp; \ >+})
It would get closer to the original if you used "=g" (I noticed in a few earlier patches already that you like to use "=r" in places where a register is not strictly required, thus reducing the flexibility the compiler has).
Also, given that this is more a workaround for a compiler deficiency, shouldn't this be conditional upon use of LTO?
Jan
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