[PATCH] powerpc/xmon: avoid warnings about variables that might be clobbered by ‘longjmp’

Move initialization of variables after data definitions. This silence
warnings treated as error with W=1:

  arch/powerpc/xmon/xmon.c:3389:14: error: variable ‘name’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
  arch/powerpc/xmon/xmon.c:3100:22: error: variable ‘tsk’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]

Signed-off-by: Mathieu Malaterre <redacted>
---
 arch/powerpc/xmon/xmon.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 47166ad2a669..982848c784ff 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c

@@ -3097,10 +3097,11 @@ static void show_pte(unsigned long addr)
 static void show_tasks(void)
 {
 	unsigned long tskv;
-	struct task_struct *tsk = NULL;
+	struct task_struct *tsk;
 
 	printf("     task_struct     ->thread.ksp    PID   PPID S  P CMD\n");
 
+	tsk = NULL;
 	if (scanhex(&tskv))
 		tsk = (struct task_struct *)tskv;
 

@@ -3386,10 +3387,11 @@ static void xmon_print_symbol(unsigned long address, const char *mid,
 			      const char *after)
 {
 	char *modname;
-	const char *name = NULL;
+	const char *name;
 	unsigned long offset, size;
 
 	printf(REG, address);
+	name = NULL;
 	if (setjmp(bus_error_jmp) == 0) {
 		catch_memory_errors = 1;
 		sync();

-- 
2.11.0

Le 22/06/2018 à 21:27, Mathieu Malaterre a écrit :

Move initialization of variables after data definitions. This silence
warnings treated as error with W=1:

   arch/powerpc/xmon/xmon.c:3389:14: error: variable ‘name’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
   arch/powerpc/xmon/xmon.c:3100:22: error: variable ‘tsk’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]

Is that an invalid warning ?

If so, please explain in the commit log.

Otherwise, I'd expect one to fix the warning, not just cheat on GCC.

Christophe

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On Sat, Jun 23, 2018 at 06:59:27PM +0200, christophe leroy wrote:

Le 22/06/2018 à 21:27, Mathieu Malaterre a écrit :

quoted

Move initialization of variables after data definitions. This silence
warnings treated as error with W=1:

  arch/powerpc/xmon/xmon.c:3389:14: error: variable ‘name’ might be 
  clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
  arch/powerpc/xmon/xmon.c:3100:22: error: variable ‘tsk’ might be 
  clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]

Is that an invalid warning ?

No, both are correct warnings.  GCC can not see which functions it only
has a declaration of can call longjmp.

Otherwise, I'd expect one to fix the warning, not just cheat on GCC.

Yes, the patch seems to change the code in such a way that some versions
of GCC will no longer warn.  Which does not make to code any more correct.

Either restructure the code, or make the var non-automatic, or make it
volatile.


Segher

On Sat, Jun 23, 2018 at 9:47 PM Segher Boessenkool
[off-list ref] wrote:

On Sat, Jun 23, 2018 at 06:59:27PM +0200, christophe leroy wrote:

quoted

Le 22/06/2018 =C3=A0 21:27, Mathieu Malaterre a =C3=A9crit :

quoted

Move initialization of variables after data definitions. This silence
warnings treated as error with W=3D1:

  arch/powerpc/xmon/xmon.c:3389:14: error: variable =E2=80=98name=E2=

=80=99 might be

quoted

quoted

  clobbered by =E2=80=98longjmp=E2=80=99 or =E2=80=98vfork=E2=80=99 [=

-Werror=3Dclobbered]

quoted

quoted

  arch/powerpc/xmon/xmon.c:3100:22: error: variable =E2=80=98tsk=E2=

=80=99 might be

quoted

quoted

  clobbered by =E2=80=98longjmp=E2=80=99 or =E2=80=98vfork=E2=80=99 [=

-Werror=3Dclobbered]

quoted

Is that an invalid warning ?

No, both are correct warnings.  GCC can not see which functions it only
has a declaration of can call longjmp.

I assumed those were false positive warnings, given how easy it was to
defeat them. Let give it another try.

quoted

Otherwise, I'd expect one to fix the warning, not just cheat on GCC.

Yes, the patch seems to change the code in such a way that some versions
of GCC will no longer warn.  Which does not make to code any more correct=

.

Either restructure the code, or make the var non-automatic, or make it
volatile.


Segher