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perf unwind: Fix segbase for ld.lld linked objects

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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@nullri.ch>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: llvm@lists.linux.dev
Link: https://github.com/ClangBuiltLinux/linux/issues/1646
Link: https://lore.kernel.org/r/20220527182039.673248-1-maskray@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Fangrui Song 2022-05-27 11:20:39 -07:00 committed by Arnaldo Carvalho de Melo
parent 4f52ca1358
commit dc2cf4ca86
2 changed files with 77 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
tools/perf/util/dso.h
View File

@ -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 */

101
tools/perf/util/unwind-libunwind-local.c
View File

@ -169,29 +169,63 @@ 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;
goto out_err;
if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
break;
goto out_err;
offset = shdr.sh_offset;
} while (0);
*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 offset;
return retval;
}
#ifndef NO_LIBUNWIND_DEBUG_FRAME
@ -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);
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,