Messages in this thread | | | Date | Sat, 18 Mar 2000 09:31:23 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: Serious bug in save_flags |
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On Sun, 19 Mar 2000, Alan Modra wrote: > > Unless I'm very much mistaken, I've hit a bad problem with save_flags and > restore_flags on x86 with --fomit-frame-pointer.
You're mistaken.
The magic to know about is that the x86 will, for a "pop" instruction, use the %esp _after_ the pop for any modrm calculations, so
pushfl popl 0x18(%esp)
the "0x18(%esp)" address will be calculated using %esp after the popl, which is obviously the same as the %esp before the pushfl, which in turn is exactly what gcc thinks it should be.
Of course, this didn't used to be true - one of the changes between the 286 and the 386 was exactly this "which %esp will be used" issue (or maybe it was between the 186 and the 286 - quite a long time ago, in any case). However, it had been an undocumented issue until then, and it IS documented now.
Linus
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