* checkstack.pl <large_number>
@ 2005-02-18 19:12 Randy.Dunlap
2005-02-21 12:38 ` Jörn Engel
0 siblings, 1 reply; 2+ messages in thread
From: Randy.Dunlap @ 2005-02-18 19:12 UTC (permalink / raw)
To: joern, lkml
Hi,
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?
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 $0xc0000000,%edx
or I can just ignore it, like I've been doing for awhile...
--
~Randy
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: checkstack.pl <large_number>
2005-02-18 19:12 checkstack.pl <large_number> Randy.Dunlap
@ 2005-02-21 12:38 ` Jörn Engel
0 siblings, 0 replies; 2+ messages in thread
From: Jörn Engel @ 2005-02-21 12:38 UTC (permalink / raw)
To: Randy.Dunlap; +Cc: lkml
On Fri, 18 February 2005 11:12:45 -0800, Randy.Dunlap wrote:
>
> In checkstack.pl, do you recall the reason for this code snippet:
>
> if ($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
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2005-02-21 12:38 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-02-18 19:12 checkstack.pl <large_number> Randy.Dunlap
2005-02-21 12:38 ` Jörn Engel
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).