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f5b095924d
This is to support per-cpu variable access often without a matching DWARF entry. For some reason, I cannot find debug info of per-cpu variables sometimes. They have more complex pattern to calculate the address of per-cpu variables like below. 2b7d: mov -0x1e0(%rbp),%rax ; rax = cpu 2b84: mov -0x7da0f7e0(,%rax,8),%rcx ; rcx = __per_cpu_offset[cpu] * 2b8c: mov 0x34870(%rcx),%rax ; *(__per_cpu_offset[cpu] + 0x34870) Let's assume the rax register has a number for a CPU at 2b7d. The next instruction is to get the per-cpu offset' for that cpu. The offset -0x7da0f7e0 is 0xffffffff825f0820 in u64 which is the address of the '__per_cpu_offset' array in my system. So it'd get the actual offset of that CPU's per-cpu region and save it to the rcx register. Then, at 2b8c, accesses using rcx can be handled same as the global variable access. To handle this case, it should check if the offset of the instruction matches to the address of '__per_cpu_offset'. Signed-off-by: Namhyung Kim <namhyung@kernel.org> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Ian Rogers <irogers@google.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Link: https://lore.kernel.org/r/20240319055115.4063940-20-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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