On Fri, 18 February 2005 11:12:45 -0800, Randy.Dunlap wrote:
>
> In checkstack.pl, do you recall the reason for this code snippet:
>
> if ($size > 0x80000000) {
> $size = - $size;
> $size += 0x80000000;
> $size += 0x80000000;
> }
>
> There is one (unusual:) case where it fails. Is it needed?
Something like this is needed, also for unusual cases. gcc sometimes
decides to switch "sub 16" with "add -16". Later, when the stack
frame is popped back, the exchange goes vice versa.
Without this code, you'd see a few cases of nearly 4GiB.
> For arch/i386/kernel/efi_stub.S, checkstack reports:
>
> 0xc0116f5d efi_call_phys: 1073741824
> which is 0x4000_0000 (_ added for readability only), however the
> actual change in %esp there is __PAGE_OFFSET (0xc000_0000 on ia32),
>
> so if I alter the "if" test above to check for > 0xf000_0000,
> checkstack reports the correct value:
> 0xc0116f5d efi_call_phys: 3221225472
> which is 0xc000_0000.
>
>
> from objdump of efi_stub.o:
> 5: 81 ea 00 00 00 c0 sub $0xc0000000,%edx
>
> or I can just ignore it, like I've been doing for awhile...
Changing 0x8000_0000 to 0xf000_0000 would work for the add case as
well. Sounds like a sane change.
Checkstack could also do the ignoring for you, maybe like this:
if ($size > 0xf0000000) {
$size = - $size;
$size += 0x80000000;
$size += 0x80000000;
}
if ($size > 0x10000000) {
$size = 0;
}
Jörn
--
Ninety percent of everything is crap.
-- Sturgeon's Law
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