The die_find_variable_by_reg() will search for a variable or a parameter
sub-DIE in the given scope DIE where the location matches to the given
register.
For the simpliest and most common case, memory access usually happens
with a base register and an offset to the field so the register would
hold a pointer in a variable or function parameter. Then we can find
one if it has a location expression at the (instruction) address. So
this function only handles such a simple case for now.
In this case, the expression would have a DW_OP_regN operation where
N < 32. If the register index (N) is greater than or equal to 32,
DW_OP_regx operation with an operand which saves the value for the N
would be used. It would reject expressions with more operations.
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/dwarf-aux.c | 67 +++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 12 +++++++
2 files changed, 79 insertions(+)
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 10aa32334d6f..652e6e7368a2 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1245,6 +1245,73 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
out:
return ret;
}
+
+/* Interval parameters for __die_find_var_reg_cb() */
+struct find_var_data {
+ /* Target instruction address */
+ Dwarf_Addr pc;
+ /* Target register */
+ unsigned reg;
+};
+
+/* Max number of registers DW_OP_regN supports */
+#define DWARF_OP_DIRECT_REGS 32
+
+/* Only checks direct child DIEs in the given scope. */
+static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
+{
+ struct find_var_data *data = arg;
+ int tag = dwarf_tag(die_mem);
+ ptrdiff_t off = 0;
+ Dwarf_Attribute attr;
+ Dwarf_Addr base, start, end;
+ Dwarf_Op *ops;
+ size_t nops;
+
+ if (tag != DW_TAG_variable && tag != DW_TAG_formal_parameter)
+ return DIE_FIND_CB_SIBLING;
+
+ if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
+ return DIE_FIND_CB_SIBLING;
+
+ while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
+ /* Assuming the location list is sorted by address */
+ if (end < data->pc)
+ continue;
+ if (start > data->pc)
+ break;
+
+ /* Only match with a simple case */
+ if (data->reg < DWARF_OP_DIRECT_REGS) {
+ if (ops->atom == (DW_OP_reg0 + data->reg) && nops == 1)
+ return DIE_FIND_CB_END;
+ } else {
+ if (ops->atom == DW_OP_regx && ops->number == data->reg &&
+ nops == 1)
+ return DIE_FIND_CB_END;
+ }
+ }
+ return DIE_FIND_CB_SIBLING;
+}
+
+/**
+ * die_find_variable_by_reg - Find a variable saved in a register
+ * @sc_die: a scope DIE
+ * @pc: the program address to find
+ * @reg: the register number to find
+ * @die_mem: a buffer to save the resulting DIE
+ *
+ * Find the variable DIE accessed by the given register.
+ */
+Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
+ Dwarf_Die *die_mem)
+{
+ struct find_var_data data = {
+ .pc = pc,
+ .reg = reg,
+ };
+ return die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
+}
#endif
/*
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index f9d765f80fb0..b6f430730bd1 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -137,6 +137,10 @@ int die_get_scopes(Dwarf_Die *cu_die, Dwarf_Addr pc, Dwarf_Die **scopes);
/* Get byte offset range of given variable DIE */
int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
+/* Find a variable saved in the 'reg' at given address */
+Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
+ Dwarf_Die *die_mem);
+
#else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
@@ -146,6 +150,14 @@ static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
return -ENOTSUP;
}
+static inline Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die __maybe_unused,
+ Dwarf_Addr pc __maybe_unused,
+ int reg __maybe_unused,
+ Dwarf_Die *die_mem __maybe_unused)
+{
+ return NULL;
+}
+
#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
#endif /* _DWARF_AUX_H */
--
2.42.0.869.gea05f2083d-goog
|