Le 24/01/2020 à 06:46, Michael Ellerman a écrit :
Christophe Leroy <christophe.le...@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.le...@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
