Messages in this thread | | | From | Jiri Olsa <> | Date | Sun, 29 May 2022 22:14:45 +0200 | Subject | Re: [PATCH v2] perf: Fix segbase for ld.lld linked objects |
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On Sat, May 28, 2022 at 07:49:13AM -0700, Ian Rogers wrote: > On Sat, May 28, 2022 at 5:06 AM Jiri Olsa <olsajiri@gmail.com> wrote: > > > > On Fri, May 27, 2022 at 11:20:39AM -0700, Fangrui Song 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 (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> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1646 > > > Signed-off-by: Fangrui Song <maskray@google.com> > > > Cc: Ian Rogers <irogers@google.com> > > > > nice, is this a problem for libdw dwarf unwind as well? > > libdw also is broken with lld but not bfd. When I switch on verbose > output (-vv) with perf report I see: > > overlapping maps: > 202000-203000 0 a.out > 202000-203000 0 a.out > > and: > > unwind: failed with 'address range overlaps an existing module' > > The sense I get from this is libdw is rejecting the file before > anything we can do in perf.
Jan, any idea if can this be fixed in libdw?
thanks, jirka
> > Thanks, > Ian > > > you should be able to build it with: > > > > $ make NO_LIBUNWIND=1 > > > > thanks, > > jirka > > > > > > > > -- > > > 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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