perf/x86/utils: Fix uninitialized var in get_branch_type()

offset is passed as a pointer and on certain call path is not set by the
function. If the caller does not re-initialize offset between calls, value
could be inherited between calls. Prevent this by initializing offset on each
call.

This impacts the code in amd_pmu_lbr_filter() which does:

   for(i=0; ...) {
       ret = get_branch_type_fused(..., &offset);
       if (offset)
          lbr_entries[i].from += offset;
   }

Fixes: df3e9612f758 ("perf/x86: Make branch classifier fusion-aware")
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sandipan Das <sandipan.das@amd.com>
Link: https://lore.kernel.org/r/20220928184043.408364-2-eranian@google.com

diff --git a/arch/x86/events/utils.c b/arch/x86/events/utils.c
index 5f5617a..76b1f8b 100644 (file)
--- a/arch/x86/events/utils.c
+++ b/arch/x86/events/utils.c
@@ -94,6 +94,10 @@ static int get_branch_type(unsigned long from, unsigned long to, int abort,
        u8 buf[MAX_INSN_SIZE];
        int is64 = 0;
 
+       /* make sure we initialize offset */
+       if (offset)
+               *offset = 0;
+
        to_plm = kernel_ip(to) ? X86_BR_KERNEL : X86_BR_USER;
        from_plm = kernel_ip(from) ? X86_BR_KERNEL : X86_BR_USER;