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Re: [Qemu-devel] [PATCH] hw/mips_malta: Fix YAMON API print routine
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH] hw/mips_malta: Fix YAMON API print routine |
Date: |
Fri, 22 Jul 2016 15:05:39 +0200 |
User-agent: |
Mutt/1.6.0 (2016-04-01) |
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 <address@hidden>
> Cc: Aurelien Jarno <address@hidden>
> Cc: Leon Alrae <address@hidden>
> ---
> 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 <address@hidden>
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
address@hidden http://www.aurel32.net