perf unwind: 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@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>
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@ -196,7 +196,9 @@ struct dso {
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u32 status_seen;
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u32 status_seen;
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u64 file_size;
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u64 file_size;
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struct list_head open_entry;
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struct list_head open_entry;
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u64 elf_base_addr;
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u64 debug_frame_offset;
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u64 debug_frame_offset;
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u64 eh_frame_hdr_addr;
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u64 eh_frame_hdr_offset;
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u64 eh_frame_hdr_offset;
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} data;
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} data;
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/* bpf prog information */
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/* bpf prog information */
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@ -169,29 +169,63 @@ static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
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__v; \
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__v; \
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})
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})
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static u64 elf_section_offset(int fd, const char *name)
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static int elf_section_address_and_offset(int fd, const char *name, u64 *address, u64 *offset)
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{
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{
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Elf *elf;
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Elf *elf;
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GElf_Ehdr ehdr;
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GElf_Ehdr ehdr;
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GElf_Shdr shdr;
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GElf_Shdr shdr;
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u64 offset = 0;
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int ret;
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elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
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elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
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if (elf == NULL)
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if (elf == NULL)
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return -1;
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if (gelf_getehdr(elf, &ehdr) == NULL)
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goto out_err;
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if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
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goto out_err;
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*address = shdr.sh_addr;
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*offset = shdr.sh_offset;
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ret = 0;
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out_err:
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elf_end(elf);
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return ret;
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}
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#ifndef NO_LIBUNWIND_DEBUG_FRAME
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static u64 elf_section_offset(int fd, const char *name)
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{
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u64 address, offset;
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if (elf_section_address_and_offset(fd, name, &address, &offset))
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return 0;
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return 0;
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do {
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return offset;
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if (gelf_getehdr(elf, &ehdr) == NULL)
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}
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break;
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#endif
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if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
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static u64 elf_base_address(int fd)
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break;
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{
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Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
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GElf_Phdr phdr;
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u64 retval = 0;
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size_t i, phdrnum = 0;
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offset = shdr.sh_offset;
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if (elf == NULL)
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} while (0);
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return 0;
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(void)elf_getphdrnum(elf, &phdrnum);
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/* PT_LOAD segments are sorted by p_vaddr, so the first has the minimum p_vaddr. */
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for (i = 0; i < phdrnum; i++) {
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if (gelf_getphdr(elf, i, &phdr) && phdr.p_type == PT_LOAD) {
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retval = phdr.p_vaddr & -getpagesize();
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break;
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}
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}
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elf_end(elf);
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elf_end(elf);
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return offset;
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return retval;
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}
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}
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#ifndef NO_LIBUNWIND_DEBUG_FRAME
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#ifndef NO_LIBUNWIND_DEBUG_FRAME
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@ -248,8 +282,7 @@ struct eh_frame_hdr {
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} __packed;
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} __packed;
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static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
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static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
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u64 offset, u64 *table_data, u64 *segbase,
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u64 offset, u64 *table_data_offset, u64 *fde_count)
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u64 *fde_count)
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{
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{
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struct eh_frame_hdr hdr;
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struct eh_frame_hdr hdr;
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u8 *enc = (u8 *) &hdr.enc;
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u8 *enc = (u8 *) &hdr.enc;
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@ -265,35 +298,47 @@ static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
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dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
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dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
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*fde_count = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
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*fde_count = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
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*segbase = offset;
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*table_data_offset = enc - (u8 *) &hdr;
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*table_data = (enc - (u8 *) &hdr) + offset;
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return 0;
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return 0;
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}
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}
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static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
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static int read_unwind_spec_eh_frame(struct dso *dso, struct unwind_info *ui,
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u64 *table_data, u64 *segbase,
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u64 *table_data, u64 *segbase,
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u64 *fde_count)
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u64 *fde_count)
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{
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{
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int ret = -EINVAL, fd;
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struct map *map;
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u64 offset = dso->data.eh_frame_hdr_offset;
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u64 base_addr = UINT64_MAX;
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int ret, fd;
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if (offset == 0) {
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if (dso->data.eh_frame_hdr_offset == 0) {
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fd = dso__data_get_fd(dso, machine);
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fd = dso__data_get_fd(dso, ui->machine);
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if (fd < 0)
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if (fd < 0)
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return -EINVAL;
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return -EINVAL;
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/* Check the .eh_frame section for unwinding info */
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/* Check the .eh_frame section for unwinding info */
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offset = elf_section_offset(fd, ".eh_frame_hdr");
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ret = elf_section_address_and_offset(fd, ".eh_frame_hdr",
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dso->data.eh_frame_hdr_offset = offset;
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&dso->data.eh_frame_hdr_addr,
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&dso->data.eh_frame_hdr_offset);
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dso->data.elf_base_addr = elf_base_address(fd);
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dso__data_put_fd(dso);
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dso__data_put_fd(dso);
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if (ret || dso->data.eh_frame_hdr_offset == 0)
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return -EINVAL;
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}
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}
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if (offset)
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maps__for_each_entry(ui->thread->maps, map) {
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ret = unwind_spec_ehframe(dso, machine, offset,
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if (map->dso == dso && map->start < base_addr)
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table_data, segbase,
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base_addr = map->start;
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fde_count);
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}
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base_addr -= dso->data.elf_base_addr;
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return ret;
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/* Address of .eh_frame_hdr */
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*segbase = base_addr + dso->data.eh_frame_hdr_addr;
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ret = unwind_spec_ehframe(dso, ui->machine, dso->data.eh_frame_hdr_offset,
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table_data, fde_count);
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if (ret)
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return ret;
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/* binary_search_table offset plus .eh_frame_hdr address */
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*table_data += *segbase;
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return 0;
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}
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}
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#ifndef NO_LIBUNWIND_DEBUG_FRAME
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#ifndef NO_LIBUNWIND_DEBUG_FRAME
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@ -388,14 +433,14 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
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pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
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pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
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/* Check the .eh_frame section for unwinding info */
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/* Check the .eh_frame section for unwinding info */
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if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
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if (!read_unwind_spec_eh_frame(map->dso, ui,
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&table_data, &segbase, &fde_count)) {
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&table_data, &segbase, &fde_count)) {
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memset(&di, 0, sizeof(di));
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memset(&di, 0, sizeof(di));
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di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
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di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
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di.start_ip = map->start;
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di.start_ip = map->start;
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di.end_ip = map->end;
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di.end_ip = map->end;
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di.u.rti.segbase = map->start + segbase - map->pgoff;
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di.u.rti.segbase = segbase;
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di.u.rti.table_data = map->start + table_data - map->pgoff;
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di.u.rti.table_data = table_data;
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di.u.rti.table_len = fde_count * sizeof(struct table_entry)
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di.u.rti.table_len = fde_count * sizeof(struct table_entry)
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/ sizeof(unw_word_t);
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/ sizeof(unw_word_t);
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ret = dwarf_search_unwind_table(as, ip, &di, pi,
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ret = dwarf_search_unwind_table(as, ip, &di, pi,
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