Messages in this thread | | | From | Brian Gerst <> | Date | Thu, 21 Jul 2016 23:08:40 -0400 | Subject | Re: [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments |
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On Thu, Jul 21, 2016 at 9:41 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > On Thu, Jul 21, 2016 at 02:56:52PM -0700, Andy Lutomirski wrote: >> On Thu, Jul 21, 2016 at 2:21 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: >> > When calling show_stack_log_lvl() or dump_trace() with a regs argument, >> > providing a stack pointer or frame pointer is redundant. >> > >> >> > diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c >> > index 358fe1c..c533b8b 100644 >> > --- a/arch/x86/kernel/dumpstack_32.c >> > +++ b/arch/x86/kernel/dumpstack_32.c >> > @@ -122,7 +122,7 @@ void show_regs(struct pt_regs *regs) >> > u8 *ip; >> > >> > pr_emerg("Stack:\n"); >> > - show_stack_log_lvl(NULL, regs, ®s->sp, 0, KERN_EMERG); >> > + show_stack_log_lvl(NULL, regs, NULL, 0, KERN_EMERG); >> >> This is weird -- note the &. You're at some risk of exposing a bug in >> x86_32's kernel_stack_pointer() function, which is a mess. (I don't >> see why it's written the way it is -- the actual return stack pointer >> given a pt_regs is quite well defined -- if regs->cs & 3 != 0, then >> it's regs->sp, else it's ®s->sp.) >> >> That being said, this isn't a big deal, so: >> >> Reviewed-by: Andy Lutomirski <luto@kernel.org> >> >> If you want to make this all a bit more reliably on x86_32, you could >> fix kernel_stack_pointer(). > > Ok. The whole '®s->sp' thing threw me for a loop. I have no idea > what kernel_stack_pointer() is trying to do. I just assumed it was > correct. I'll take a look at it and try to fix it in another patch.
On 32-bit, when an interrupt doesn't change CPL, SS:ESP is not pushed. So, effectively, the old stack pointer is ®s->sp.
-- Brian Gerst
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