perf annotate-data: Handle this-cpu variables in kernel

On x86, the kernel gets the current task using the current macro like
below:

  #define current  get_current()

  static __always_inline struct task_struct *get_current(void)
  {
      return this_cpu_read_stable(pcpu_hot.current_task);
  }

So it returns the current_task field of struct pcpu_hot which is the
first member.  On my build, it's located at 0x32940.

  $ nm vmlinux | grep pcpu_hot
  0000000000032940 D pcpu_hot

And the current macro generates the instructions like below:

  mov  %gs:0x32940, %rcx

So the %gs segment register points to the beginning of the per-cpu
region of this cpu and it points the variable with a constant.

Let's update the instruction location info to have a segment register
and handle %gs in kernel to look up a global variable.  Pretend it as
a global variable by changing the register number to DWARF_REG_PC.

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/20240319055115.4063940-18-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index 3aa3a3b987ad..e4121acb4f88 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -3921,6 +3921,13 @@ retry:
 							    op_loc->offset, dl);
 		}
 
+		/* This CPU access in kernel - pretend PC-relative addressing */
+		if (map__dso(ms->map)->kernel && arch__is(arch, "x86") &&
+		    op_loc->segment == INSN_SEG_X86_GS && op_loc->imm) {
+			dloc.var_addr = op_loc->offset;
+			op_loc->reg1 = DWARF_REG_PC;
+		}
+
 		mem_type = find_data_type(&dloc);
 		if (mem_type)
 			istat->good++;