Messages in this thread | | | From | Ian Rogers <> | Date | Fri, 27 May 2022 09:03:46 -0700 | Subject | Re: [PATCH] perf: Fix segbase for ld.lld linked objects |
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On Thu, May 26, 2022 at 11:49 PM Ian Rogers <irogers@google.com> wrote: > > On Thu, May 26, 2022 at 10:52 PM Fangrui Song <maskray@google.com> wrote: > > > > 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 => fail > > ld.lld --no-rosegment => ok > > ld.lld -z separate-code => ok > > > > ld.bfd -z separate-code (default for Linux/x86) => ok > > ld.bfd -z noseparate-code => ok > > > > To fix the issue, compute segbase as dso's base address plus > > PT_GNU_EH_FRAME's p_vaddr. > > > > Reported-by: Sebastian Ullrich <sebasti@nullri.ch> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1646 > > Signed-off-by: Fangrui Song <maskray@google.com> > > Cc: Ian Rogers <irogers@google.com> > > Thanks Fangrui! I tested static vs not, bfd and lld, perf test and > some hand tests. I couldn't see anything out of order. The code looks > good although there could be some ambiguity over the variables ending > _addr as these are the ELF given addresses rather than the thread's > virtual memory addresses. I'm also trying to get more comments > especially on major data structures like dso, but that can be fixed as > a follow-on. > > Tested-by: Ian Rogers <irogers@google.com> > > > --- > > tools/perf/util/dso.h | 2 + > > tools/perf/util/unwind-libunwind-local.c | 96 ++++++++++++++++-------- > > 2 files changed, 67 insertions(+), 31 deletions(-) > > > > diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h > > index 3a9fd4d389b5..ec4fc1a9454b 100644 > > --- a/tools/perf/util/dso.h > > +++ b/tools/perf/util/dso.h > > @@ -179,6 +179,7 @@ struct dso { > > bool loaded; > > u8 rel; > > struct build_id bid; > > + u64 base_addr;
This is an address in a thread, as one dso can be shared by multiple threads/processes it seems unsafe to hold it as the dso may be loaded at a different address in a different thread. For now we can just recompute the value rather than store it in the dso.
> > u64 text_offset; > > const char *short_name; > > const char *long_name; > > @@ -197,6 +198,7 @@ struct dso { > > u64 file_size; > > struct list_head open_entry; > > u64 debug_frame_offset; > > + u64 eh_frame_hdr_addr;
This is the elf section address and safe to hold here.
Thanks, Ian
> > 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..7a0053954e49 100644 > > --- a/tools/perf/util/unwind-libunwind-local.c > > +++ b/tools/perf/util/unwind-libunwind-local.c > > @@ -169,30 +169,55 @@ 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 int elf_base_address(int fd) > > +{ > > + Elf *elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL); > > + GElf_Phdr phdr; > > + int retval = 0; > > + > > + if (gelf_getphdr(elf, 0, &phdr) != NULL) > > + retval = phdr.p_vaddr & -getpagesize(); > > + > > + elf_end(elf); > > + return retval; > > +} > > > > #ifndef NO_LIBUNWIND_DEBUG_FRAME > > static int elf_is_exec(int fd, const char *name) > > @@ -248,8 +273,7 @@ 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 +289,45 @@ 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; > > + int ret, fd; > > > > - if (offset == 0) { > > - fd = dso__data_get_fd(dso, machine); > > + if (dso->data.eh_frame_hdr_offset == 0) { > > + u64 addr_min = UINT64_MAX; > > + > > + 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); > > + maps__for_each_entry(ui->thread->maps, map) { > > + if (map->dso == dso && map->start < addr_min) > > + addr_min = map->start; > > + } > > + dso->base_addr = addr_min - 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; > > + *segbase = dso->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; > > + *table_data += *segbase; > > + return 0; > > } > > > > #ifndef NO_LIBUNWIND_DEBUG_FRAME > > @@ -388,14 +422,14 @@ 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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