The die_get_cfa() is to get frame base register and offset at the given
instruction address (pc). This info will be used to locate stack
variables which have location expression using DW_OP_fbreg.
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/dwarf-aux.c | 64 +++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 9 ++++++
2 files changed, 73 insertions(+)
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 97d9ae56350e..796413eb4e8f 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1408,6 +1408,70 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
return result;
}
+static int reg_from_dwarf_op(Dwarf_Op *op)
+{
+ switch (op->atom) {
+ case DW_OP_reg0 ... DW_OP_reg31:
+ return op->atom - DW_OP_reg0;
+ case DW_OP_breg0 ... DW_OP_breg31:
+ return op->atom - DW_OP_breg0;
+ case DW_OP_regx:
+ case DW_OP_bregx:
+ return op->number;
+ default:
+ break;
+ }
+ return -1;
+}
+
+static int offset_from_dwarf_op(Dwarf_Op *op)
+{
+ switch (op->atom) {
+ case DW_OP_reg0 ... DW_OP_reg31:
+ case DW_OP_regx:
+ return 0;
+ case DW_OP_breg0 ... DW_OP_breg31:
+ return op->number;
+ case DW_OP_bregx:
+ return op->number2;
+ default:
+ break;
+ }
+ return -1;
+}
+
+/**
+ * die_get_cfa - Get frame base information
+ * @dwarf: a Dwarf info
+ * @pc: program address
+ * @preg: pointer for saved register
+ * @poffset: pointer for saved offset
+ *
+ * This function gets register and offset for CFA (Canonical Frame Address)
+ * by searching the CIE/FDE info. The CFA usually points to the start address
+ * of the current stack frame and local variables can be located using an offset
+ * from the CFA. The @preg and @poffset will be updated if it returns 0.
+ */
+int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset)
+{
+ Dwarf_CFI *cfi;
+ Dwarf_Frame *frame = NULL;
+ Dwarf_Op *ops = NULL;
+ size_t nops;
+
+ cfi = dwarf_getcfi(dwarf);
+ if (cfi == NULL)
+ return -1;
+
+ if (!dwarf_cfi_addrframe(cfi, pc, &frame) &&
+ !dwarf_frame_cfa(frame, &ops, &nops) && nops == 1) {
+ *preg = reg_from_dwarf_op(ops);
+ *poffset = offset_from_dwarf_op(ops);
+ return 0;
+ }
+ return -1;
+}
+
#endif
/*
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 742098e3ee7e..29a7243b1a45 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -149,6 +149,9 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
Dwarf_Addr addr, Dwarf_Die *die_mem,
int *offset);
+/* Get the frame base information from CFA */
+int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset);
+
#else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
@@ -175,6 +178,12 @@ static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unu
return NULL;
}
+static inline int die_get_cfa(Dwarf *dwarf __maybe_unused, u64 pc __maybe_unused,
+ int *preg __maybe_unused, int *poffset __maybe_unused)
+{
+ return -1;
+}
+
#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
#endif /* _DWARF_AUX_H */
--
2.42.0.655.g421f12c284-goog
|