Messages in this thread | | | Date | Wed, 15 Feb 2023 09:17:23 +0000 | From | Andrew Cooper <> | Subject | Re: [RFC PATCH v1 1/2] selftests/x86: sysret_rip: Handle syscall in a FRED system |
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On 26/01/2023 8:08 pm, Ammar Faizi wrote: > On Mon, Jan 23, 2023 at 05:40:23PM -0800, H. Peter Anvin wrote: >> So as per Andrew's comment, add: >> >> register void * rsp asm("%rsp"); >> >> ... >> >> "+r" (rsp) /* clobber the redzone */ >> >> ... as the right way to avoid redzone problems. > I played with this more. I found something wrong with this. This doesn't > work for me. The compiler still uses red zone despite I use "+r" (rsp). > > What did I do wrong?
Well this is a fine mess...
https://godbolt.org/z/MaPM7s8qr does the right thing, but is now contrary to the prior discussion regarding calls in asm, which concluded that the "+r"(rsp) was the way to go.
Furthermore GCC regressed in 9.0 and emits:
warning: listing the stack pointer register 'rsp' in a clobber list is deprecated [-Wdeprecated]
which might be the intention of the developers, but is wrong seeing as this is the only way to say "I modify the redzone" to the compiler...
~Andrew
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