perf probe through debuginfo__find_probes() in util/probe-finder.c
checks for the functions' frame descriptions in either .eh_frame section
of an ELF or the .debug_frame. The check is based on whether either one
of these sections is present. But sometimes, it may happen that,
.eh_frame, even if present, may not be complete and may miss some
descriptions. For e.g., in powerpc, this may happen :
$ gcc -g bin.c -o bin
$ objdump --dwarf ./bin
<1><145>: Abbrev Number: 7 (DW_TAG_subprogram)
<146> DW_AT_external : 1
<146> DW_AT_name : (indirect string, offset: 0x9e): main
<14a> DW_AT_decl_file : 1
<14b> DW_AT_decl_line : 39
<14c> DW_AT_prototyped : 1
<14c> DW_AT_type : <0x57>
<150> DW_AT_low_pc : 0x100007b8
If the .eh_frame and .debug_frame are checked for the same binary, we
will find that, .eh_frame (although present) doesn't contain a
description for "main" function.
But, .debug_frame has a description :
000000d8 00000024 00000000 FDE cie=00000000 pc=100007b8..10000838
DW_CFA_advance_loc: 16 to 100007c8
DW_CFA_def_cfa_offset: 144
DW_CFA_offset_extended_sf: r65 at cfa+16
...
Due to this (since, perf checks whether .eh_frame is present and goes on
searching for that address inside that frame), perf is unable to process
the probes :
# perf probe -x ./bin main
Failed to get call frame on 0x100007b8
Error: Failed to add events.
To avoid this issue, we need to check both the sections (.eh_frame and
.debug_frame), which is done in this patch.
Note that, we can always force everything into both .eh_frame and
.debug_frame by :
$ gcc bin.c -fasynchronous-unwind-tables -fno-dwarf2-cfi-asm -g -o bin
Signed-off-by: Hemant Kumar <hem...@linux.vnet.ibm.com>
---
tools/perf/util/probe-finder.c | 59 +++++++++++++++++++++++++-----------------
1 file changed, 35 insertions(+), 24 deletions(-)
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 2da65a7..7ce02b9 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1022,9 +1022,8 @@ static int pubname_search_cb(Dwarf *dbg, Dwarf_Global
*gl, void *data)
return DWARF_CB_OK;
}
-/* Find probe points from debuginfo */
-static int debuginfo__find_probes(struct debuginfo *dbg,
- struct probe_finder *pf)
+static int debuginfo__find_probe_location(struct debuginfo *dbg,
+ struct probe_finder *pf)
{
struct perf_probe_point *pp = &pf->pev->point;
Dwarf_Off off, noff;
@@ -1032,27 +1031,6 @@ static int debuginfo__find_probes(struct debuginfo *dbg,
Dwarf_Die *diep;
int ret = 0;
-#if _ELFUTILS_PREREQ(0, 142)
- Elf *elf;
- GElf_Ehdr ehdr;
- GElf_Shdr shdr;
-
- /* Get the call frame information from this dwarf */
- elf = dwarf_getelf(dbg->dbg);
- if (elf == NULL)
- return -EINVAL;
-
- if (gelf_getehdr(elf, &ehdr) == NULL)
- return -EINVAL;
-
- if (elf_section_by_name(elf, &ehdr, &shdr, ".eh_frame", NULL) &&
- shdr.sh_type == SHT_PROGBITS) {
- pf->cfi = dwarf_getcfi_elf(elf);
- } else {
- pf->cfi = dwarf_getcfi(dbg->dbg);
- }
-#endif
-
off = 0;
pf->lcache = intlist__new(NULL);
if (!pf->lcache)
@@ -1115,6 +1093,39 @@ found:
return ret;
}
+/* Find probe points from debuginfo */
+static int debuginfo__find_probes(struct debuginfo *dbg,
+ struct probe_finder *pf)
+{
+ int ret = 0;
+
+#if _ELFUTILS_PREREQ(0, 142)
+ Elf *elf;
+ GElf_Ehdr ehdr;
+ GElf_Shdr shdr;
+
+ /* Get the call frame information from this dwarf */
+ elf = dwarf_getelf(dbg->dbg);
+ if (elf == NULL)
+ return -EINVAL;
+
+ if (gelf_getehdr(elf, &ehdr) == NULL)
+ return -EINVAL;
+
+ if (elf_section_by_name(elf, &ehdr, &shdr, ".eh_frame", NULL) &&
+ shdr.sh_type == SHT_PROGBITS) {
+ pf->cfi = dwarf_getcfi_elf(elf);
+ ret = debuginfo__find_probe_location(dbg, pf);
+ if (ret >= 0)
+ return ret;
+ }
+ pf->cfi = dwarf_getcfi(dbg->dbg);
+#endif
+
+ ret = debuginfo__find_probe_location(dbg, pf);
+ return ret;
+}
+
struct local_vars_finder {
struct probe_finder *pf;
struct perf_probe_arg *args;
--
1.9.3
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