The find_data_type() is to get a data type from the memory access at the
given address (IP) using a register and an offset. It requires DWARF
debug info in the DSO and searches the list of variables and function
parameters in the scope.
In a pseudo code, it does basically the following:
find_data_type(dso, ip, reg, offset)
{
pc = map__rip_2objdump(ip);
CU = dwarf_addrdie(dso->dwarf, pc);
scopes = die_get_scopes(CU, pc);
for_each_scope(S, scopes) {
V = die_find_variable_by_reg(S, pc, reg);
if (V && V.type == pointer_type) {
T = die_get_real_type(V);
if (offset < T.size)
return T;
}
}
return NULL;
}
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/Build | 1 +
tools/perf/util/annotate-data.c | 163 ++++++++++++++++++++++++++++++++
tools/perf/util/annotate-data.h | 40 ++++++++
3 files changed, 204 insertions(+)
create mode 100644 tools/perf/util/annotate-data.c
create mode 100644 tools/perf/util/annotate-data.h
Hi Arnaldo,
On Sat, Nov 11, 2023 at 10:55 AM Arnaldo Carvalho de Melo
<arnaldo.melo@gmail.com> wrote:
>
> On Thu, Nov 9, 2023, 9:00 PM Namhyung Kim <namhyung@kernel.org> wrote:
>>
>>
>> +static bool find_cu_die(struct debuginfo *di, u64 pc, Dwarf_Die *cu_die)
>> +{
>> + Dwarf_Off off, next_off;
>> + size_t header_size;
>> +
>> + if (dwarf_addrdie(di->dbg, pc, cu_die) != NULL)
>> + return cu_die;
>
> Isn't the return type a bool?
>
> Shouldn't be 'return true;'?
>
> Ends up like that as cu_die isn't NULL, but looks confusing.
Ok, will change.
>
>> +
>> + /*
>> + * There are some kernels don't have full aranges and contain only a few
>> + * aranges entries. Fallback to iterate all CU entries in .debug_info
>> + * in case it's missing.
>> + */
>> + off = 0;
>> + while (dwarf_nextcu(di->dbg, off, &next_off, &header_size,
>> + NULL, NULL, NULL) == 0) {
>> + if (dwarf_offdie(di->dbg, off + header_size, cu_die) &&
>> + dwarf_haspc(cu_die, pc))
>> + return true;
>> +
>> + off = next_off;
>> + }
>> + return false;
>> +}
>> +
>>
>> +struct annotated_data_type *find_data_type(struct map_symbol *ms, u64 ip,
>> + int reg, int offset)
>> +{
>> + struct annotated_data_type *result = NULL;
>> + struct dso *dso = ms->map->dso;
>> + struct debuginfo *di;
>> + Dwarf_Die type_die;
>> + struct strbuf sb;
>> + u64 pc;
>> +
>> + di = debuginfo__new(dso->long_name);
>> + if (di == NULL) {
>> + pr_debug("cannot get the debug info\n");
>
>
> Shouldn't inform the dso->long_name and function name to ease debugging?
Sounds good, I'll update it in the v3.
Thanks,
Namhyung
@@ -196,6 +196,7 @@ perf-$(CONFIG_DWARF) += probe-finder.o
perf-$(CONFIG_DWARF) += dwarf-aux.o
perf-$(CONFIG_DWARF) += dwarf-regs.o
perf-$(CONFIG_DWARF) += debuginfo.o
+perf-$(CONFIG_DWARF) += annotate-data.o
perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind-local.o
new file mode 100644
@@ -0,0 +1,163 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Convert sample address to data type using DWARF debug info.
+ *
+ * Written by Namhyung Kim <namhyung@kernel.org>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "annotate-data.h"
+#include "debuginfo.h"
+#include "debug.h"
+#include "dso.h"
+#include "map.h"
+#include "map_symbol.h"
+#include "strbuf.h"
+#include "symbol.h"
+
+static bool find_cu_die(struct debuginfo *di, u64 pc, Dwarf_Die *cu_die)
+{
+ Dwarf_Off off, next_off;
+ size_t header_size;
+
+ if (dwarf_addrdie(di->dbg, pc, cu_die) != NULL)
+ return cu_die;
+
+ /*
+ * There are some kernels don't have full aranges and contain only a few
+ * aranges entries. Fallback to iterate all CU entries in .debug_info
+ * in case it's missing.
+ */
+ off = 0;
+ while (dwarf_nextcu(di->dbg, off, &next_off, &header_size,
+ NULL, NULL, NULL) == 0) {
+ if (dwarf_offdie(di->dbg, off + header_size, cu_die) &&
+ dwarf_haspc(cu_die, pc))
+ return true;
+
+ off = next_off;
+ }
+ return false;
+}
+
+/* The type info will be saved in @type_die */
+static int check_variable(Dwarf_Die *var_die, Dwarf_Die *type_die, int offset)
+{
+ Dwarf_Word size;
+
+ /* Get the type of the variable */
+ if (die_get_real_type(var_die, type_die) == NULL) {
+ pr_debug("variable has no type\n");
+ return -1;
+ }
+
+ /*
+ * It expects a pointer type for a memory access.
+ * Convert to a real type it points to.
+ */
+ if (dwarf_tag(type_die) != DW_TAG_pointer_type ||
+ die_get_real_type(type_die, type_die) == NULL) {
+ pr_debug("no pointer or no type\n");
+ return -1;
+ }
+
+ /* Get the size of the actual type */
+ if (dwarf_aggregate_size(type_die, &size) < 0) {
+ pr_debug("type size is unknown\n");
+ return -1;
+ }
+
+ /* Minimal sanity check */
+ if ((unsigned)offset >= size) {
+ pr_debug("offset: %d is bigger than size: %lu\n", offset, size);
+ return -1;
+ }
+
+ return 0;
+}
+
+/* The result will be saved in @type_die */
+static int find_data_type_die(struct debuginfo *di, u64 pc,
+ int reg, int offset, Dwarf_Die *type_die)
+{
+ Dwarf_Die cu_die, var_die;
+ Dwarf_Die *scopes = NULL;
+ int ret = -1;
+ int i, nr_scopes;
+
+ /* Get a compile_unit for this address */
+ if (!find_cu_die(di, pc, &cu_die)) {
+ pr_debug("cannot find CU for address %lx\n", pc);
+ return -1;
+ }
+
+ /* Get a list of nested scopes - i.e. (inlined) functions and blocks. */
+ nr_scopes = die_get_scopes(&cu_die, pc, &scopes);
+
+ /* Search from the inner-most scope to the outer */
+ for (i = nr_scopes - 1; i >= 0; i--) {
+ /* Look up variables/parameters in this scope */
+ if (!die_find_variable_by_reg(&scopes[i], pc, reg, &var_die))
+ continue;
+
+ /* Found a variable, see if it's correct */
+ ret = check_variable(&var_die, type_die, offset);
+ break;
+ }
+
+ free(scopes);
+ return ret;
+}
+
+/**
+ * find_data_type - Return a data type at the location
+ * @ms: map and symbol at the location
+ * @ip: instruction address of the memory access
+ * @reg: register that holds the base address
+ * @offset: offset from the base address
+ *
+ * This functions searches the debug information of the binary to get the data
+ * type it accesses. The exact location is expressed by (ip, reg, offset).
+ * It return %NULL if not found.
+ */
+struct annotated_data_type *find_data_type(struct map_symbol *ms, u64 ip,
+ int reg, int offset)
+{
+ struct annotated_data_type *result = NULL;
+ struct dso *dso = ms->map->dso;
+ struct debuginfo *di;
+ Dwarf_Die type_die;
+ struct strbuf sb;
+ u64 pc;
+
+ di = debuginfo__new(dso->long_name);
+ if (di == NULL) {
+ pr_debug("cannot get the debug info\n");
+ return NULL;
+ }
+
+ /*
+ * IP is a relative instruction address from the start of the map, as
+ * it can be randomized/relocated, it needs to translate to PC which is
+ * a file address for DWARF processing.
+ */
+ pc = map__rip_2objdump(ms->map, ip);
+ if (find_data_type_die(di, pc, reg, offset, &type_die) < 0)
+ goto out;
+
+ result = zalloc(sizeof(*result));
+ if (result == NULL)
+ goto out;
+
+ strbuf_init(&sb, 32);
+ if (die_get_typename_from_type(&type_die, &sb) < 0)
+ strbuf_add(&sb, "(unknown type)", 14);
+
+ result->type_name = strbuf_detach(&sb, NULL);
+
+out:
+ debuginfo__delete(di);
+ return result;
+}
new file mode 100644
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _PERF_ANNOTATE_DATA_H
+#define _PERF_ANNOTATE_DATA_H
+
+#include <errno.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+struct map_symbol;
+
+/**
+ * struct annotated_data_type - Data type to profile
+ * @type_name: Name of the data type
+ * @type_size: Size of the data type
+ *
+ * This represents a data type accessed by samples in the profile data.
+ */
+struct annotated_data_type {
+ char *type_name;
+ int type_size;
+};
+
+#ifdef HAVE_DWARF_SUPPORT
+
+/* Returns data type at the location (ip, reg, offset) */
+struct annotated_data_type *find_data_type(struct map_symbol *ms, u64 ip,
+ int reg, int offset);
+
+#else /* HAVE_DWARF_SUPPORT */
+
+static inline struct annotated_data_type *
+find_data_type(struct map_symbol *ms __maybe_unused, u64 ip __maybe_unused,
+ int reg __maybe_unused, int offset __maybe_unused)
+{
+ return NULL;
+}
+
+#endif /* HAVE_DWARF_SUPPORT */
+
+#endif /* _PERF_ANNOTATE_DATA_H */