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Message-Id: <20220527182039.673248-1-maskray@google.com>
Date: Fri, 27 May 2022 11:20:39 -0700
From: Fangrui Song <maskray@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Ian Rogers <irogers@...gle.com>, llvm@...ts.linux.dev,
Fangrui Song <maskray@...gle.com>,
Sebastian Ullrich <sebasti@...lri.ch>
Subject: [PATCH v2] perf: Fix segbase for ld.lld linked objects
segbase is the address of .eh_frame_hdr and table_data is segbase plus
the header size. find_proc_info computes segbase as `map->start +
segbase - map->pgoff` which is wrong when
* .eh_frame_hdr and .text are in different PT_LOAD program headers
* and their p_vaddr difference does not equal their p_offset difference
Since 10.0, ld.lld's default --rosegment -z noseparate-code layout has
such R and RX PT_LOAD program headers.
ld.lld (default) => perf report fails to unwind `perf record
--call-graph dwarf` recorded data
ld.lld --no-rosegment => ok (trivial, no R PT_LOAD)
ld.lld -z separate-code => ok but by luck: there are two PT_LOAD but
their p_vaddr difference equals p_offset difference
ld.bfd -z noseparate-code => ok (trivial, no R PT_LOAD)
ld.bfd -z separate-code (default for Linux/x86) => ok but by luck:
there are two PT_LOAD but their p_vaddr difference equals p_offset
difference
To fix the issue, compute segbase as dso's base address plus
PT_GNU_EH_FRAME's p_vaddr. The base address is computed by iterating
over all dso-associated maps and then subtract the first PT_LOAD p_vaddr
(the minimum guaranteed by generic ABI) from the minimum address.
In libunwind, find_proc_info transitively called by unw_step is cached,
so the iteration overhead is acceptable.
Reported-by: Sebastian Ullrich <sebasti@...lri.ch>
Link: https://github.com/ClangBuiltLinux/linux/issues/1646
Signed-off-by: Fangrui Song <maskray@...gle.com>
Cc: Ian Rogers <irogers@...gle.com>
--
Changes from v1:
* Fix elf_base_address to use the first PT_LOAD
* Use dso::elf_base_addr which is a constant even if the dso is loaded into multiple processes
---
tools/perf/util/dso.h | 2 +
tools/perf/util/unwind-libunwind-local.c | 107 ++++++++++++++++-------
2 files changed, 78 insertions(+), 31 deletions(-)
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 3a9fd4d389b5..97047a11282b 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -196,7 +196,9 @@ struct dso {
u32 status_seen;
u64 file_size;
struct list_head open_entry;
+ u64 elf_base_addr;
u64 debug_frame_offset;
+ u64 eh_frame_hdr_addr;
u64 eh_frame_hdr_offset;
} data;
/* bpf prog information */
diff --git a/tools/perf/util/unwind-libunwind-local.c b/tools/perf/util/unwind-libunwind-local.c
index 41e29fc7648a..37622699c91a 100644
--- a/tools/perf/util/unwind-libunwind-local.c
+++ b/tools/perf/util/unwind-libunwind-local.c
@@ -169,30 +169,64 @@ static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
__v; \
})
-static u64 elf_section_offset(int fd, const char *name)
+static int elf_section_address_and_offset(int fd, const char *name, u64 *address, u64 *offset)
{
Elf *elf;
GElf_Ehdr ehdr;
GElf_Shdr shdr;
- u64 offset = 0;
+ int ret;
elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
if (elf == NULL)
- return 0;
+ return -1;
- do {
- if (gelf_getehdr(elf, &ehdr) == NULL)
- break;
+ if (gelf_getehdr(elf, &ehdr) == NULL)
+ goto out_err;
- if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
- break;
-
- offset = shdr.sh_offset;
- } while (0);
+ if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
+ goto out_err;
+ *address = shdr.sh_addr;
+ *offset = shdr.sh_offset;
+ ret = 0;
+out_err:
elf_end(elf);
+ return ret;
+}
+
+#ifndef NO_LIBUNWIND_DEBUG_FRAME
+static u64 elf_section_offset(int fd, const char *name)
+{
+ u64 address, offset;
+
+ if (elf_section_address_and_offset(fd, name, &address, &offset))
+ return 0;
+
return offset;
}
+#endif
+
+static u64 elf_base_address(int fd)
+{
+ Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+ GElf_Phdr phdr;
+ u64 retval = 0;
+ size_t i, phdrnum = 0;
+
+ if (elf == NULL)
+ return 0;
+ (void)elf_getphdrnum(elf, &phdrnum);
+ /* PT_LOAD segments are sorted by p_vaddr, so the first has the minimum p_vaddr. */
+ for (i = 0; i < phdrnum; i++) {
+ if (gelf_getphdr(elf, i, &phdr) && phdr.p_type == PT_LOAD) {
+ retval = phdr.p_vaddr & -getpagesize();
+ break;
+ }
+ }
+
+ elf_end(elf);
+ return retval;
+}
#ifndef NO_LIBUNWIND_DEBUG_FRAME
static int elf_is_exec(int fd, const char *name)
@@ -248,8 +282,7 @@ struct eh_frame_hdr {
} __packed;
static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
- u64 offset, u64 *table_data, u64 *segbase,
- u64 *fde_count)
+ u64 offset, u64 *table_data_offset, u64 *fde_count)
{
struct eh_frame_hdr hdr;
u8 *enc = (u8 *) &hdr.enc;
@@ -265,35 +298,47 @@ static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
*fde_count = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
- *segbase = offset;
- *table_data = (enc - (u8 *) &hdr) + offset;
+ *table_data_offset = enc - (u8 *) &hdr;
return 0;
}
-static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
+static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,
u64 *table_data, u64 *segbase,
u64 *fde_count)
{
- int ret = -EINVAL, fd;
- u64 offset = dso->data.eh_frame_hdr_offset;
+ struct map *map;
+ u64 base_addr = UINT64_MAX;
+ int ret, fd;
- if (offset == 0) {
- fd = dso__data_get_fd(dso, machine);
+ if (dso->data.eh_frame_hdr_offset == 0) {
+ fd = dso__data_get_fd(dso, ui->machine);
if (fd < 0)
return -EINVAL;
/* Check the .eh_frame section for unwinding info */
- offset = elf_section_offset(fd, ".eh_frame_hdr");
- dso->data.eh_frame_hdr_offset = offset;
+ ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",
+ &dso->data.eh_frame_hdr_addr,
+ &dso->data.eh_frame_hdr_offset);
+ dso->data.elf_base_addr = elf_base_address(fd);
dso__data_put_fd(dso);
+ if (ret || dso->data.eh_frame_hdr_offset == 0)
+ return -EINVAL;
}
- if (offset)
- ret = unwind_spec_ehframe(dso, machine, offset,
- table_data, segbase,
- fde_count);
-
- return ret;
+ maps__for_each_entry(ui->thread->maps, map) {
+ if (map->dso == dso && map->start < base_addr)
+ base_addr = map->start;
+ }
+ base_addr -= dso->data.elf_base_addr;
+ /* Address of .eh_frame_hdr */
+ *segbase = base_addr + dso->data.eh_frame_hdr_addr;
+ ret = unwind_spec_ehframe(dso, ui->machine, dso->data.eh_frame_hdr_offset,
+ table_data, fde_count);
+ if (ret)
+ return ret;
+ /* binary_search_table offset plus .eh_frame_hdr address */
+ *table_data += *segbase;
+ return 0;
}
#ifndef NO_LIBUNWIND_DEBUG_FRAME
@@ -388,14 +433,14 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
pr_debug("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,
+ if (!read_unwind_spec_eh_frame(map->dso, ui,
&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 - map->pgoff;
- di.u.rti.table_data = map->start + table_data - map->pgoff;
+ di.u.rti.segbase = segbase;
+ di.u.rti.table_data = table_data;
di.u.rti.table_len = fde_count * sizeof(struct table_entry)
/ sizeof(unw_word_t);
ret = dwarf_search_unwind_table(as, ip, &di, pi,
--
2.36.1.124.g0e6072fb45-goog
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