linux-kernel - Silence compiler warning in arch/x86/kvm/emulate.c

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Message-ID: <142668.1440884956@turing-police.cc.vt.edu>
Date:	Sat, 29 Aug 2015 17:49:16 -0400
From:	Valdis Kletnieks <Valdis.Kletnieks@...edu>
To:	Gleb Natapov <gleb@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>
cc:	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Aruna Hewapathirane <aruna.hewapathirane@...il.com>
Subject: Silence compiler warning in  arch/x86/kvm/emulate.c

Compiler warning:

 CC [M]  arch/x86/kvm/emulate.o
arch/x86/kvm/emulate.c: In function "__do_insn_fetch_bytes":
arch/x86/kvm/emulate.c:814:9: warning: "linear" may be used uninitialized in this function [-Wmaybe-uninitialized]

GCC is smart enough to realize that the inlined __linearize may return before
setting the value of linear, but not smart enough to realize the same
X86EMU_CONTINUE blocks actual use of the value.  However, the value of
'linear' can only be set to one value, so hoisting the one line of code
upwards makes GCC happy with the code.

Reported-by: Aruna Hewapathirane <aruna.hewapathirane@...il.com>
Tested-by: Aruna Hewapathirane <aruna.hewapathirane@...il.com>
Signed-off-by: Valdis Kletnieks <valdis.kletnieks@...edu>

--- a/arch/x86/kvm/emulate.c.dist	2015-08-11 14:10:05.366061993 -0400
+++ b/arch/x86/kvm/emulate.c	2015-08-29 13:43:13.014163958 -0400
@@ -650,6 +650,7 @@ static __always_inline int __linearize(s
 	u16 sel;
 
 	la = seg_base(ctxt, addr.seg) + addr.ea;
+	*linear = la;
 	*max_size = 0;
 	switch (mode) {
 	case X86EMUL_MODE_PROT64:
@@ -693,7 +694,6 @@ static __always_inline int __linearize(s
 	}
 	if (insn_aligned(ctxt, size) && ((la & (size - 1)) != 0))
 		return emulate_gp(ctxt, 0);
-	*linear = la;
 	return X86EMUL_CONTINUE;
 bad:
 	if (addr.seg == VCPU_SREG_SS)

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