[PATCH 17/23] perf annotate-data: Handle this-cpu variables in kernel

[Namhyung Kim]

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@xxxxxxxxxx>
---
 tools/perf/util/annotate-data.c | 21 +++++++++++++++++++--
 tools/perf/util/annotate.c      |  7 +++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index f5329a78a97d..d57622ddd5d3 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -790,7 +790,7 @@ static void delete_var_types(struct die_var_type *var_types)
 /* It's at the target address, check if it has a matching type */
 static bool check_matching_type(struct type_state *state,
 				struct data_loc_info *dloc, int reg,
-				Dwarf_Die *type_die)
+				Dwarf_Die *cu_die, Dwarf_Die *type_die)
 {
 	Dwarf_Word size;
 	u32 insn_offset = dloc->ip - dloc->ms->sym->start;
@@ -864,6 +864,23 @@ static bool check_matching_type(struct type_state *state,
 		return true;
 	}
 
+	if (map__dso(dloc->ms->map)->kernel && arch__is(dloc->arch, "x86")) {
+		u64 addr;
+		int offset;
+
+		if (dloc->op->segment == INSN_SEG_X86_GS && dloc->op->imm) {
+			pr_debug_dtp(" this-cpu var\n");
+
+			addr = dloc->op->offset;
+
+			if (get_global_var_type(cu_die, dloc, dloc->ip, addr,
+						&offset, type_die)) {
+				dloc->type_offset = offset;
+				return true;
+			}
+		}
+	}
+
 	pr_debug_dtp("\n");
 	return false;
 }
@@ -897,7 +914,7 @@ static bool find_data_type_insn(struct data_loc_info *dloc, int reg,
 
 			if (this_ip == dloc->ip) {
 				found = check_matching_type(&state, dloc, reg,
-							    type_die);
+							    cu_die, type_die);
 				goto out;
 			}
 
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 @@ struct annotated_data_type *hist_entry__get_data_type(struct hist_entry *he)
 							    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++;
-- 
2.44.0.291.gc1ea87d7ee-goog