From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f49.google.com (mail-wr1-f49.google.com [209.85.221.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9C66B1FC8 for ; Fri, 27 May 2022 18:52:08 +0000 (UTC) Received: by mail-wr1-f49.google.com with SMTP id q20so2408647wrc.10 for ; Fri, 27 May 2022 11:52:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=6mnq6s94t7HVDlK1KKnF1BOHF1n74alGQX0XJ6Y9vKE=; b=BR3zd/vBbmw1kqJ+9veXoJPVyr84j7xUtlwS+kx2VF6cEeRX56XW2ceoNXenDm9cZF 2+DmTQCWed/9NzrE3uAczYkvyLQ484ZJfmb7Jq99BEeHPk/dCA4R4tNBMp9ptoB6DLjR 4RhF4sPLrM7ojQITMHh/++RTnYQ8wqRDWhyUZd7j/V1axvFB0KABe07CqLntG8G6unap CYUOysMLIuOsOf6dO2599uUE2wbyLoj3UshMAZ8oF5nwCkY/iRREw0X4yFGJ8RrKHyKn 2dQIMVyCFq4qPRqviXpWzvrQNbjJW7qZRPywaMLukSHwzb8qtFq4jTRAN7VD2NsD1x1R 5qVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6mnq6s94t7HVDlK1KKnF1BOHF1n74alGQX0XJ6Y9vKE=; b=6NqtZsUWRK/bjVVNUNfQgccrJcWzcTMZLdE3a9brqQBEL4YTy9OyMs1J3kPoR14tG6 9LyNfrbLJBiNbgJ7WDz3BYoxz8ZhJPG9kl9GKNiQYdHUSYuazuf8frMWr82OYBGL552D x+YEd4j1OB3yTMOrtxdYfBl/V3m8ab2b7J7jeCdWIBQVqvmuL1ELJ4yqkMY6ITCjKAY9 MD+sh9au9IrvnVUKq35O42q9jLtqaoPtq8kWNMt3Xs+nHX8pZUDVGYRSdOWjB8bJpv/s 70RAkSddZfSY9P+tYzP9+WTTG4/OWT2fSQANKnj8OJurHdziKFPSn2za9Sl7Gk51CgH9 GYCw== X-Gm-Message-State: AOAM532pSWnHYBTxxAu0RcXq0wpTmtrwDVPyY/qavoElIWywp0aSqizo 6rYDd/a8YBnOUzGVQrxI4kgdyj+0Mtbb4986altELA== X-Google-Smtp-Source: ABdhPJzInRoKCYogfXHEE4xel1G0d7QXLMHln0xOKGtmqeWL3sU5RFq0Efp5yPiLAgMVa1MHVNXDl5F+Bm5iOr/g/9o= X-Received: by 2002:a5d:598f:0:b0:20c:83c9:b05b with SMTP id n15-20020a5d598f000000b0020c83c9b05bmr36529153wri.343.1653677526611; Fri, 27 May 2022 11:52:06 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20220527182039.673248-1-maskray@google.com> In-Reply-To: <20220527182039.673248-1-maskray@google.com> From: Ian Rogers Date: Fri, 27 May 2022 11:51:54 -0700 Message-ID: Subject: Re: [PATCH v2] perf: Fix segbase for ld.lld linked objects To: Fangrui Song Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Sebastian Ullrich Content-Type: text/plain; charset="UTF-8" On Fri, May 27, 2022 at 11:20 AM 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 > Link: https://github.com/ClangBuiltLinux/linux/issues/1646 > Signed-off-by: Fangrui Song > Cc: Ian Rogers Reviewed-by: Ian Rogers Thanks! Ian > -- > 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 >