Re: Fwd: perf: callchain feature on ARM - question about libunwindAPI
From: David Ahern
Date: Tue Aug 27 2013 - 12:12:18 EST
[Added Jiri who added the feature to perf]
On 8/27/13 5:58 AM, Jean Pihet wrote:
Hi!
I am looking for info and help on the libunwind API.
What I am trying to achieve is to allow the callchain feature on perf
for ARM (v7 to start with, then ARMv8), from the DWARF info found in
the .debug_frame section.
From the source code in tools/perf I have added the call to
dwarf_find_debug_frame to load and parse the debug info from
.debug_frame. This works correctly, all IP ranges are found from the
debug code (test program and libraries). Then at some point I get an
assertion: 'perf: dwarf/Gparser.c:459: fetch_proc_info: Assertion
`c->pi.unwind_info' failed.' At that point c->pi is NULL. Cf. below
for more info.
It looks like I am not using the libunwind API as it should, so that
the perf code apparently builds a list of IP ranges to resolve but
cannot use it later on to gather statistics on the runtime info.
Any idea on how to progress? I am also looking at the *_proc_info API
of libunwind.
Here is the patch I am using below.
Cheers,
Jean
---
Debug log:
perf report --sort symbol --call-graph --stdio
_Uarm_step: calling dwarf_step(ip=0x8464, c->dwarf@0xbee150f8,
c->dwarf.pi@0xb2bc0008)
unwind: find_proc_info dso /home/linaro/perf-libunwind/
test_app/stress_bt
read_unwind_spec_debug_frame: .debug_frame offset=9304
opened file '/home/linaro/perf-libunwind/test_app/stress_bt'. Section
header at offset 18152
read 3160 bytes of .debug_frame from offset 9304
...
_ULarm_step: calling dwarf_step(ip=0xb6e6e764, c->dwarf@0xbee07508,
c->dwarf.pi@0xb6e955c0)
_ULarm_find_proc_info: looking for IP=0xb6e6e763
opened file '/usr/lib/arm-linux-gnueabihf/libunwind.so.8'. Section
header at offset 513260
read 17072 bytes of .debug_frame from offset 451836
_ULarm_dwarf_search_unwind_table: looking for IP=0xb6e6e763
_ULarm_find_proc_info returns 0
...
perf: dwarf/Gparser.c:459: fetch_proc_info: Assertion
`c->pi.unwind_info' failed.
---
Patch to the kernel source:
diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
index 958723b..dd97688 100644
--- a/tools/perf/util/unwind.c
+++ b/tools/perf/util/unwind.c
@@ -39,6 +39,14 @@ UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
+extern int
+UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
+ unw_word_t ip, unw_word_t segbase,
+ const char* obj_name, unw_word_t start,
+ unw_word_t end);
+
+#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
+
#define DW_EH_PE_FORMAT_MASK 0x0f /* format of the encoded value */
#define DW_EH_PE_APPL_MASK 0x70 /* how the value is to be applied */
@@ -245,8 +253,9 @@ static int unwind_spec_ehframe(struct dso *dso,
struct machine *machine,
return 0;
}
-static int read_unwind_spec(struct dso *dso, struct machine *machine,
- u64 *table_data, u64 *segbase, u64 *fde_count)
+static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
+ u64 *table_data, u64 *segbase,
+ u64 *fde_count)
{
int ret = -EINVAL, fd;
u64 offset;
@@ -255,18 +264,40 @@ static int read_unwind_spec(struct dso *dso,
struct machine *machine,
if (fd < 0)
return -EINVAL;
+ /* Check the .eh_frame section for unwinding info */
offset = elf_section_offset(fd, ".eh_frame_hdr");
close(fd);
- if (offset)
+ if (offset) {
+ fprintf(stderr, "%s: .eh_frame offset=%llu\n", __func__, offset);
ret = unwind_spec_ehframe(dso, machine, offset,
table_data, segbase,
fde_count);
+ }
- /* TODO .debug_frame check if eh_frame_hdr fails */
return ret;
}
+static int read_unwind_spec_debug_frame(struct dso *dso,
+ struct machine *machine,
+ u64 *segbase)
+{
+ int fd = dso__data_fd(dso, machine);
+ if (fd < 0)
+ return -EINVAL;
+
+ /* Check the .debug_frame section for unwinding info */
+ *segbase = elf_section_offset(fd, ".debug_frame");
+ close(fd);
+
+ fprintf(stderr, "%s: .debug_frame offset=%llu\n", __func__, *segbase);
+
+ if (!segbase)
+ return -EINVAL;
+
+ return 0;
+}
+
static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
{
struct addr_location al;
@@ -289,22 +320,32 @@ find_proc_info(unw_addr_space_t as, unw_word_t
ip, unw_proc_info_t *pi,
if (!map || !map->dso)
return -EINVAL;
- pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
+ fprintf(stderr, "unwind: find_proc_info dso %s\n", map->dso->name);
+
+ /* Check the .eh_frame section for unwinding info */
+ if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
+ &table_data, &segbase, &fde_count)) {
+ memset(&di, 0, sizeof(di));
+ di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
+ di.start_ip = map->start;
+ di.end_ip = map->end;
+ di.u.rti.segbase = map->start + segbase;
+ di.u.rti.table_data = map->start + table_data;
+ di.u.rti.table_len = fde_count * sizeof(struct table_entry)
+ / sizeof(unw_word_t);
+ return dwarf_search_unwind_table(as, ip, &di, pi,
+ need_unwind_info, arg);
+ }
- if (read_unwind_spec(map->dso, ui->machine,
- &table_data, &segbase, &fde_count))
- return -EINVAL;
+ /* Check the .debug_frame section for unwinding info */
+ if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
+ memset(&di, 0, sizeof(di));
+ if (dwarf_find_debug_frame(0, &di, ip, segbase, map->dso->name,
+ map->start, map->end))
+ return 0;
+ }
- memset(&di, 0, sizeof(di));
- di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
- di.start_ip = map->start;
- di.end_ip = map->end;
- di.u.rti.segbase = map->start + segbase;
- di.u.rti.table_data = map->start + table_data;
- di.u.rti.table_len = fde_count * sizeof(struct table_entry)
- / sizeof(unw_word_t);
- return dwarf_search_unwind_table(as, ip, &di, pi,
- need_unwind_info, arg);
+ return -EINVAL;
}
static int access_fpreg(unw_addr_space_t __maybe_unused as,
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