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Re: [Qemu-ppc] [PATCH] Fix missing TRACE exception
From: |
Alexander Graf |
Subject: |
Re: [Qemu-ppc] [PATCH] Fix missing TRACE exception |
Date: |
Fri, 23 Nov 2012 17:06:23 +0100 |
On 19.10.2012, at 12:17, Julio Guerra wrote:
> This patch fixes bug 1031698 :
> https://bugs.launchpad.net/qemu/+bug/1031698
>
> If we look at the (truncated) translation of the conditional branch
> instruction in the test submitted in the bug post, the call to the
> exception helper is missing in the "bne-false" chunk of translated
> code :
>
> IN:
> bne- 0x1800278
>
> OUT:
> 0xb544236d: jne 0xb5442396
>
> 0xb5442373: mov %ebp,(%esp)
> 0xb5442376: mov $0x44,%ebx
> 0xb544237b: mov %ebx,0x4(%esp)
> 0xb544237f: mov $0x1800278,%ebx
> 0xb5442384: mov %ebx,0x25c(%ebp)
> 0xb544238a: call 0x827475a
> ^^^^^^^^^^^^^^^^^^
> # OK : call the exception helper function
>
> 0xb5442396: mov %ebp,(%esp)
> 0xb5442399: mov $0x44,%ebx
> 0xb544239e: mov %ebx,0x4(%esp)
> 0xb54423a2: mov $0x1800270,%ebx
> 0xb54423a7: mov %ebx,0x25c(%ebp)
> # KO : missing "call 0x827475a"
>
>
> Indeed, gen_exception(ctx, excp) called by gen_goto_tb (called by
> gen_bcond) changes ctx->exception's value to excp's :
>
> gen_bcond()
> {
> gen_goto_tb(ctx, 0, ctx->nip + li - 4);
> /* ctx->exception value is POWERPC_EXCP_BRANCH */
>
> gen_goto_tb(ctx, 1, ctx->nip);
> /* ctx->exception now value is POWERPC_EXCP_TRACE */
> }
>
>
> Making the following gen_goto_tb()'s test false during the second call :
>
> if ((ctx->singlestep_enabled &
> (CPU_BRANCH_STEP | CPU_SINGLE_STEP)) &&
> ctx->exception == POWERPC_EXCP_BRANCH /* false...*/) {
> target_ulong tmp = ctx->nip;
> ctx->nip = dest;
> /* ... and this is the missing call */
> gen_exception(ctx, POWERPC_EXCP_TRACE);
> ctx->nip = tmp;
> }
>
> So the patch simply adds the missing matching case, fixing our problem.
>
> Signed-off-by: Julio Guerra <address@hidden>
Thanks, applied to ppc-next :)
Alex
> ---
> target-ppc/translate.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff -up a/target-ppc/translate.c b/target-ppc/translate.c
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -3466,7 +3466,8 @@ static inline void gen_goto_tb(DisasCont
> if (unlikely(ctx->singlestep_enabled)) {
> if ((ctx->singlestep_enabled &
> (CPU_BRANCH_STEP | CPU_SINGLE_STEP)) &&
> - ctx->exception == POWERPC_EXCP_BRANCH) {
> + (ctx->exception == POWERPC_EXCP_BRANCH ||
> + ctx->exception == POWERPC_EXCP_TRACE)) {
> target_ulong tmp = ctx->nip;
> ctx->nip = dest;
> gen_exception(ctx, POWERPC_EXCP_TRACE);