Messages in this thread | | | Date | Thu, 26 Aug 2021 08:47:58 -0500 | From | Segher Boessenkool <> | Subject | Re: [PATCH v2 2/2] powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with asm goto |
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On Thu, Aug 26, 2021 at 08:37:09AM +0200, Christophe Leroy wrote: > Le 26/08/2021 à 05:21, Michael Ellerman a écrit : > >This patch seems to fix it. Not sure if that's just papering over it > >though. > > > >diff --git a/arch/powerpc/include/asm/bug.h > >b/arch/powerpc/include/asm/bug.h > >index 1ee0f22313ee..75fcb4370d96 100644 > >--- a/arch/powerpc/include/asm/bug.h > >+++ b/arch/powerpc/include/asm/bug.h > >@@ -119,7 +119,7 @@ __label_warn_on: \ > > \ > > WARN_ENTRY(PPC_TLNEI " %4, 0", \ > > BUGFLAG_WARNING | > > BUGFLAG_TAINT(TAINT_WARN), \ > >- __label_warn_on, "r" (x)); \ > >+ __label_warn_on, "r" (!!(x))); \ > > break; \ > > __label_warn_on: \ > > __ret_warn_on = true; \ > > But for a simple WARN_ON() call: > > void test(unsigned long b) > { > WARN_ON(b); > } > > Without your change with GCC you get: > > 00000000000012d0 <.test>: > 12d0: 0b 03 00 00 tdnei r3,0 > 12d4: 4e 80 00 20 blr > > > With the !! change you get: > > 00000000000012d0 <.test>: > 12d0: 31 23 ff ff addic r9,r3,-1 > 12d4: 7d 29 19 10 subfe r9,r9,r3 > 12d8: 0b 09 00 00 tdnei r9,0 > 12dc: 4e 80 00 20 blr
That is because the asm (unlike the builtin) cannot be optimised by the compiler.
Segher
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