Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 2/3] tools/nolibc: i386: fix initial stack alignment | Date | Mon, 25 Oct 2021 07:46:11 +0000 |
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From: Willy Tarreau > Sent: 24 October 2021 18:28 > > After re-checking in the spec and comparing stack offsets with glibc, > The last pushed argument must be 16-byte aligned (i.e. aligned before the > call) so that in the callee esp+4 is multiple of 16, so the principle is > the 32-bit equivalent to what Ammar fixed for x86_64. It's possible that > 32-bit code using SSE2 or MMX could have been affected. In addition the > frame pointer ought to be zero at the deepest level. > ... > /* startup code */ > +/* > + * i386 System V ABI mandates: > + * 1) last pushed argument must be 16-byte aligned. > + * 2) The deepest stack frame should be set to zero
I'm pretty sure that the historic SYSV i386 ABI only every required 4-byte alignment for the stack.
At some point it got 'randomly' changed to 16-byte. I don't think this happened until after compiler support for SSE2 intrinsics was added. ISTR the NetBSD found that it was gcc that moved the goalposts.
David
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