Messages in this thread |  | | Subject | Re: [PATCH 1/2] powerpc/irq: don't use current_stack_pointer() in check_stack_overflow() | From | Christophe Leroy <> | Date | Fri, 24 Jan 2020 07:19:57 +0100 |
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Le 24/01/2020 à 06:46, Michael Ellerman a écrit : > Christophe Leroy <christophe.leroy@c-s.fr> writes: > >> current_stack_pointer() doesn't return the stack pointer, but the >> caller's stack frame. See commit bfe9a2cfe91a ("powerpc: Reimplement >> __get_SP() as a function not a define") and commit acf620ecf56c >> ("powerpc: Rename __get_SP() to current_stack_pointer()") for details. >> >> The purpose of check_stack_overflow() is to verify that the stack has >> not overflowed. >> >> To really know whether the stack pointer is still within boundaries, >> the check must be done directly on the value of r1. >> >> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> >> --- >> arch/powerpc/kernel/irq.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c >> index bb34005ff9d2..4d468d835558 100644 >> --- a/arch/powerpc/kernel/irq.c >> +++ b/arch/powerpc/kernel/irq.c >> @@ -599,9 +599,8 @@ u64 arch_irq_stat_cpu(unsigned int cpu) >> static inline void check_stack_overflow(void) >> { >> #ifdef CONFIG_DEBUG_STACKOVERFLOW >> - long sp; >> - >> - sp = current_stack_pointer() & (THREAD_SIZE-1); >> + register unsigned long r1 asm("r1"); >> + long sp = r1 & (THREAD_SIZE - 1); > > This appears to work but seems to be "unsupported" by GCC, and clang > actually complains about it: > > /linux/arch/powerpc/kernel/irq.c:603:12: error: variable 'r1' is uninitialized when used here [-Werror,-Wuninitialized] > long sp = r1 & (THREAD_SIZE - 1); > ^~ > > The GCC docs say: > > The only supported use for this feature is to specify registers for > input and output operands when calling Extended asm (see Extended > Asm). > > https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Local-Register-Variables.html#Local-Register-Variables > > > If I do this it seems to work, but feels a little dicey: > > asm ("" : "=r" (r1)); > sp = r1 & (THREAD_SIZE - 1);
Or we could do add in asm/reg.h what we have in boot/reg.h:
register void *__stack_pointer asm("r1"); #define get_sp() (__stack_pointer)
And use get_sp()
I'll try it.
Christophe
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