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Merged
vadimskipin merged 1 commit into from
May 6, 2026
Merged

Add a comment about handling bpf_map_lookup_elem error #9

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12 changes: 10 additions & 2 deletions src/profiler/profiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -204,13 +204,21 @@ void Profiler::collect(Symbolizer * symbolizer)
uint64_t userAddrs[MAX_FRAMES] = {};
uint64_t kernelAddrs[MAX_FRAMES] = {};

// UINT32_MAX is the sentinel the BPF program stores when bpf_get_stackid
// fails (normalizes all negative errno values to -1, which becomes
// 0xFFFFFFFF when cast to u32). Valid stack IDs are always non-negative
// s32 values and never alias UINT32_MAX.
//
// On lookup failure (stack ID evicted between map iteration and lookup)
// the arrays remain zero-initialized, countFrames returns 0, and the
// sample is skipped by the nUser == 0 && nKernel == 0 check below.
if (userSid != UINT32_MAX)
{
bpf_map_lookup_elem(stackFd, &userSid, userAddrs);
(void)bpf_map_lookup_elem(stackFd, &userSid, userAddrs);
}
if (kernelSid != UINT32_MAX)
{
bpf_map_lookup_elem(stackFd, &kernelSid, kernelAddrs);
(void)bpf_map_lookup_elem(stackFd, &kernelSid, kernelAddrs);
}

int nUser = countFrames(userAddrs);
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