Messages in this thread | | | Date | Tue, 12 May 2009 10:20:46 -0400 | From | Masami Hiramatsu <> | Subject | Re: [PATCH -rc] [BUGFIX] x86: fix kernel_trap_sp() |
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Robin Holt wrote: > On Mon, May 11, 2009 at 03:24:07PM -0700, Linus Torvalds wrote: >> >> On Mon, 11 May 2009, Masami Hiramatsu wrote: >>> Use ®s->sp instead of regs for getting the top of stack in kernel mode. >>> (on x86-64, regs->sp always points the top of stack) >> Ack. >> >> That said, we have only _one_ use of this "kernel_trap_sp()" in the whole >> kernel, and that use is actually fairly odd too, in that it does it >> _before_ checking that it's in kernel mode. >> >> Admittedly it will then only _use_ the value after it has checked that >> things are in kernel mode, but it all boils down to "ok, that's pretty >> odd". >> >> So how about fixing that, and also fixing the naming of the function. Call >> it "kernel_stack_pointer()" to match its more widely used sibling function >> "user_stack_pointer()". >> >> IOW, something like this? >> >> Linus >> >> --- >> arch/x86/include/asm/ptrace.h | 7 ++++--- >> arch/x86/oprofile/backtrace.c | 2 +- >> 2 files changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h >> index e304b66..624f133 100644 >> --- a/arch/x86/include/asm/ptrace.h >> +++ b/arch/x86/include/asm/ptrace.h >> @@ -187,14 +187,15 @@ static inline int v8086_mode(struct pt_regs *regs) >> >> /* >> * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode >> - * when it traps. So regs will be the current sp. >> + * when it traps. The previous stack will be directly underneath the saved >> + * registers, and 'sp/ss' won't even have been saved. Thus the '®s->sp'. >> * >> * This is valid only for kernel mode traps. >> */ >> -static inline unsigned long kernel_trap_sp(struct pt_regs *regs) >> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) > > Why not have it return an unsigned long *? >> { >> #ifdef CONFIG_X86_32 >> - return (unsigned long)regs; >> + return (unsigned long)(®s->sp); >> #else >> return regs->sp;
Perhaps, you might forget that this line needs a cast :-).
Anyway, IMHO, it does not come from coding, but meaning. kernel/user_stack_pointer() just return "the value of stack pointer register", not a "stack pointer".
Thank you,
>> #endif >> diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c >> index 04df67f..044897b 100644 >> --- a/arch/x86/oprofile/backtrace.c >> +++ b/arch/x86/oprofile/backtrace.c >> @@ -76,9 +76,9 @@ void >> x86_backtrace(struct pt_regs * const regs, unsigned int depth) >> { >> struct frame_head *head = (struct frame_head *)frame_pointer(regs); >> - unsigned long stack = kernel_trap_sp(regs); >> >> if (!user_mode_vm(regs)) { >> + unsigned long stack = kernel_stack_pointer(regs); > > Make this an unsigned long *? > >> if (depth) >> dump_trace(NULL, regs, (unsigned long *)stack, 0, > > Then get rid of the cast? > > Robin
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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