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[Qemu-devel] [PATCH for-2.6] target-sparc: fix ldstub sign-extension bug

From: Mark Cave-Ayland
Subject: [Qemu-devel] [PATCH for-2.6] target-sparc: fix ldstub sign-extension bug
Date: Sat, 9 Apr 2016 12:43:32 +0100

ldstub [addr], reg incorrectly reads a signed byte from memory which causes
problems in the 32-bit Solaris mutex code. Here the byte value being read is
0xff which is incorrectly sign-extended to 0xffffffff before being written back
to the target register causing lock detection to behave incorrectly.

This fixes the intermittent hangs and MUTEX_HELD warnings issued to the
console when running 32-bit Solaris images under qemu-system-sparc.

With thanks to Joseph Dery for providing a condensed test image to consistently
reproduce the problem on demand, and Martin Husemann for allowing me access to
real hardware for comparison.

Signed-off-by: Mark Cave-Ayland <address@hidden>
 target-sparc/translate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target-sparc/translate.c b/target-sparc/translate.c
index 58572c3..7998ff5 100644
--- a/target-sparc/translate.c
+++ b/target-sparc/translate.c
@@ -4670,7 +4670,7 @@ static void disas_sparc_insn(DisasContext * dc, unsigned 
int insn)
                         TCGv r_const;
                         gen_address_mask(dc, cpu_addr);
-                        tcg_gen_qemu_ld8s(cpu_val, cpu_addr, dc->mem_idx);
+                        tcg_gen_qemu_ld8u(cpu_val, cpu_addr, dc->mem_idx);
                         r_const = tcg_const_tl(0xff);
                         tcg_gen_qemu_st8(r_const, cpu_addr, dc->mem_idx);

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