[Xen-changelog] [qemu-upstream-unstable] PPC: Fix missing TRACE exception

[patchbot@xxxxxxx]

commit f0cc4aa8450376ca2aee3ebb09db71f9f2ff333b
Author: Julio Guerra <guerr@xxxxxxxx>
Date:   Fri Oct 19 00:17:13 2012 +0000

    PPC: Fix missing TRACE exception
    
    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
                         ^^^^^^^^^^^^^^^^^^
    
    0xb5442396:  mov    %ebp,(%esp)
    0xb5442399:  mov    $0x44,%ebx
    0xb544239e:  mov    %ebx,0x4(%esp)
    0xb54423a2:  mov    $0x1800270,%ebx
    0xb54423a7:  mov    %ebx,0x25c(%ebp)
    
    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 <guerr@xxxxxxxx>
    Signed-off-by: Alexander Graf <agraf@xxxxxxx>
---
 target-ppc/translate.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/target-ppc/translate.c b/target-ppc/translate.c
index 16b9c5d..987b04e 100644
--- a/target-ppc/translate.c
+++ b/target-ppc/translate.c
@@ -3473,7 +3473,8 @@ static inline void gen_goto_tb(DisasContext *ctx, int n, 
target_ulong dest)
         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);
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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