Messages in this thread | | | Date | Wed, 25 Mar 1998 11:03:01 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] APM support doesn't compile with binutils 2.8.1.0.24 |
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On Wed, 25 Mar 1998, MOLNAR Ingo wrote: > > On Wed, 25 Mar 1998, Linus Torvalds wrote: > > > So I think the APM bios access code is actually correct in specifying a > > "l" on the push/pop operations. > > pushl %ds has better alignment and it pairs better with other 32-bit > instructions. pushl %%ds does zero-extend. movl %%ds, %%eax does > zero-extend as well, so the behavior seems to be symmetric. (i've just > tested this to be sure ;).
No. "pushl" does not zero-extend reliably: test it on older intel chips and you'll see (the i386 at least only wrote the low 16 bits, I think the same is true of the 486 but I wouldn't bet on the latter). Also, look at the behaviour of "movl %ds,mem", to see the case where it doesn't write the high bits at all.
Linus
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