Hi Tommi,

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.

Regards, Jean

--- Log:

_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,