On Mon, Oct 25, 2021 at 07:46:11AM +0000, David Laight wrote: > 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. It's very possible because I've done a number of tests and noticed that in some cases the called functions' stack doesn't seem to be more than 4-aligned. However the deepest function in the stack starts with an aligned stack so I prefer to follow this same rule. Willy
