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Re: amd64 signal stack alignment
On Tue, May 13, 2014 at 9:57 AM, Masao Uebayashi <uebayasi%gmail.com@localhost>
> 562 /* Allocate space for the signal handler context. */
> 563 if (onstack)
> 564 sp = ((char *)l->l_sigstk.ss_sp + l->l_sigstk.ss_size);
> 565 else
> 566 /* AMD64 ABI 128-bytes "red zone". */
> 567 sp = (char *)tf->tf_rsp - 128;
> 569 sp -= sizeof(struct sigframe_siginfo);
> 570 /* Round down the stackpointer to a multiple of 16 for the ABI.
> 571 fp = (struct sigframe_siginfo *)(((unsigned long)sp & ~15) - 8);
> These calculation is very unclear to me. IIUC:
> - 8-bytes fxsave is saved below "red zone" with 8-bytes alignment, and
fxsave saved on stack was not part of ABI but just an implementation.
Now it's no longer on stack but in pcb, right? If yes the "- 8" can
> - sigframe_siginfo is written below fxsave (above initial signal SP)
> - Initial signal SP is 16-bytes aligned
> FreeBSD/amd64 sendsig() is much clearer.
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