Re: [Qemu-devel] [PATCH] hw/mips_malta: Fix YAMON API print routine

[Aurelien Jarno <aurelien@aurel32.net>]

On 2016-07-22 10:55, Paul Burton wrote:
> The print routine provided as part of the in-built bootloader had a bug
> in that it attempted to use a jump instruction as part of a loop, but
> the target has its upper bits zeroed leading to control flow
> transferring to 0xb0000814 rather than the intended 0xbfc00814. Fix this
> by using a branch instruction instead, which seems more fit for purpose.
> 
> A simple way to test this is to build a Linux kernel with EVA enabled &
> attempt to boot it in QEMU. It will attempt to print a message
> indicating the configuration mismatch but QEMU would previously
> incorrectly jump & wind up printing a continuous stream of the letter E.
> 
> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> Cc: Aurelien Jarno <aurelien@aurel32.net>
> Cc: Leon Alrae <leon.alrae@imgtec.com>
> ---
>  hw/mips/mips_malta.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> index 34d41ef..e90857e 100644
> --- a/hw/mips/mips_malta.c
> +++ b/hw/mips/mips_malta.c
> @@ -727,7 +727,7 @@ static void write_bootloader(uint8_t *base, int64_t run_addr,
>      stl_p(p++, 0x00000000);                                     /* nop */
>      stl_p(p++, 0x0ff0021c);                                     /* jal 870 */
>      stl_p(p++, 0x00000000);                                     /* nop */
> -    stl_p(p++, 0x08000205);                                     /* j 814 */
> +    stl_p(p++, 0x1000fff9);                                     /* b 814 */
>      stl_p(p++, 0x00000000);                                     /* nop */
>      stl_p(p++, 0x01a00009);                                     /* jalr t5 */
>      stl_p(p++, 0x01602021);                                     /* move a0,t3 */

This looks fine. The switch from jump to branch is questionable given
there are other jumps around in the code, but that's just nitpicking.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net