linux-kernel - [PATCH 1/3] powerpc: don't use __WARN() for WARN

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Date:   Mon, 19 Aug 2019 13:06:28 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        segher@...nel.crashing.org,
        Drew Davenport <ddavenport@...omium.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 1/3] powerpc: don't use __WARN() for WARN_ON()

__WARN() used to just call __WARN_TAINT(TAINT_WARN)

But a call to printk() has been added in the commit identified below
to print a "---- cut here ----" line.

This change only applies to warnings using __WARN(), which means
WARN_ON() where the condition is constant at compile time.
For WARN_ON() with a non constant condition, the additional line is
not printed.

In addition, adding a call to printk() forces GCC to add a stack frame
and save volatile registers. Powerpc has been using traps to implement
warnings in order to avoid that.

So, call __WARN_TAINT(TAINT_WARN) directly instead of using __WARN()
in order to restore the previous behaviour.

If one day powerpc wants the decorative "---- cut here ----" line, it
has to be done in the trap handler, not in the WARN_ON() macro.

Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/include/asm/bug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index fed7e6241349..3928fdaebb71 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -99,7 +99,7 @@
 	int __ret_warn_on = !!(x);				\
 	if (__builtin_constant_p(__ret_warn_on)) {		\
 		if (__ret_warn_on)				\
-			__WARN();				\
+			__WARN_TAINT(TAINT_WARN);		\
 	} else {						\
 		__asm__ __volatile__(				\
 		"1:	"PPC_TLNEI"	%4,0\n"			\
-- 
2.13.3