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

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

[Mark Cave-Ayland]

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 <mark.cave-ayland@ilande.co.uk>
---
 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);
                         tcg_temp_free(r_const);
-- 
1.7.10.4

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

[Artyom Tarasenko]

On Sat, Apr 9, 2016 at 1:43 PM, Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:
> 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 <mark.cave-ayland@ilande.co.uk>

Reviewed-By: Artyom Tarasenko <atar4qemu@gmail.com>

> ---
>  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);
>                          tcg_temp_free(r_const);
> --
> 1.7.10.4
>



-- 
Regards,
Artyom Tarasenko

SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu