Applies to 2.6.35 (git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux-2.6.git perf/core branch)
The new patch loads the ELF section headers from a separate file if necessary, to avoid getting confused by the different section file offsets seen in debug images. Invalid section headers are detected by checking for the presence of non- writable SHT_NOBITS sections, which don't make sense under normal circumstances.
In particular, this allows symbols in ET_EXEC images to get fixed up correctly in the presence of separated debug images.
The image search loop is also tidied up to fix a minor bug which would perform the same image load attempt more than once in some situations.
For non-separated images, the headers should get loaded from the same image as the symbols, in the usual way.
Signed-off-by: Dave Martin dave.martin@linaro.org --- tools/perf/util/symbol.c | 185 +++++++++++++++++++++++++++++++++++++++++++--- 1 files changed, 173 insertions(+), 12 deletions(-)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 1a36773..21ae9df 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -1,4 +1,5 @@ #define _GNU_SOURCE +#include <assert.h> #include <ctype.h> #include <dirent.h> #include <errno.h> @@ -978,8 +979,106 @@ static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr) return -1; }
+/** + * Read all section headers, copying them into a separate array so they survive + * elf_end. + * + * @elf: the libelf instance to operate on. + * @ehdr: the elf header: this must already have been read with gelf_getehdr(). + * @count: the number of headers read is assigned to *count on successful + * return. count must not be NULL. + * + * Returns a pointer to the allocated headers, which should be deallocated with + * free() when no longer needed. + */ +static GElf_Shdr *elf_get_all_shdrs(Elf *elf, GElf_Ehdr const *ehdr, + unsigned *count) +{ + GElf_Shdr *shdrs; + Elf_Scn *scn; + unsigned max_index = 0; + unsigned i; + + shdrs = malloc(ehdr->e_shnum * sizeof *shdrs); + if (!shdrs) + return NULL; + + for (i = 0; i < ehdr->e_shnum; i++) + shdrs[i].sh_type = SHT_NULL; + + for (scn = NULL; (scn = elf_nextscn(elf, scn)); ) { + size_t j; + + /* + * Just assuming we get section 0, 1, ... in sequence may lead + * to wrong section indices. Check the index explicitly: + */ + j = elf_ndxscn(scn); + assert(j < ehdr->e_shnum); + + if (j > max_index) + max_index = j; + + if (!gelf_getshdr(scn, &shdrs[j])) + goto error; + } + + *count = max_index + 1; + return shdrs; + +error: + free(shdrs); + return NULL; +} + +/** + * Check that the section headers @shdrs reflect accurately the file data + * layout of the image that was loaded during perf record. This is generally + * not true for separated debug images generated with e.g., + * objcopy --only-keep-debug. + * + * We identify invalid files by checking for non-empty sections which are + * declared as having no file data (SHT_NOBITS) but are not writable. + * + * @shdrs: the full set of section headers, as loaded by elf_get_all_shdrs(). + * @count: the number of headers present in @shdrs. + * + * Returns 1 for valid headers, 0 otherwise. + */ +static int elf_check_shdrs_valid(GElf_Shdr const *shdrs, unsigned count) +{ + unsigned i; + + for (i = 0; i < count; i++) { + if (shdrs[i].sh_type == SHT_NOBITS && + !(shdrs[i].sh_flags & SHF_WRITE) && + shdrs[i].sh_size != 0) + return 0; + } + + return 1; +} + +/* + * Notes: + * + * If saved_shdrs is non-NULL, the section headers will be read if found, and + * will be used for address fixups. saved_shdrs_count must also be non-NULL in + * this case. This may be needed for separated debug images, since the section + * headers and symbols may need to come from separate images in that case. + * + * Note: irrespective of whether this function returns successfully, + * *saved_shdrs may get initialised if saved_shdrs is non-NULL. It is the + * caller's responsibility to free() it when non longer needed. + * + * If want_symtab == 1, this function will only load symbols from .symtab + * sections. Otherwise (want_symtab == 0), .dynsym or .symtab symbols are + * loaded. This feature is used by dso__load() to search for the best image + * to load. + */ static int dso__load_sym(struct dso *self, struct map *map, const char *name, int fd, symbol_filter_t filter, int kmodule, + GElf_Shdr **saved_shdrs, unsigned *saved_shdrs_count, int want_symtab) { struct kmap *kmap = self->kernel ? map__kmap(map) : NULL; @@ -998,6 +1097,9 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name, int nr = 0; size_t opdidx = 0;
+ if (saved_shdrs != NULL) + assert(saved_shdrs_count != NULL); + elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL); if (elf == NULL) { pr_debug("%s: cannot read %s ELF file.\n", __func__, name); @@ -1021,6 +1123,34 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name, goto out_elf_end; }
+ /* + * Copy all section headers from the image if requested and if not + * already loaded. + */ + if (saved_shdrs != NULL && *saved_shdrs == NULL) { + GElf_Shdr *shdrs; + unsigned count; + + shdrs = elf_get_all_shdrs(elf, &ehdr, &count); + if (shdrs == NULL) + goto out_elf_end; + + /* + * Only keep the headers if they reflect the actual run-time + * image's file layout: + */ + if (elf_check_shdrs_valid(shdrs, count)) { + *saved_shdrs = shdrs; + *saved_shdrs_count = count; + } else + free(shdrs); + } + + /* If no genuine ELF headers are available yet, give up: we can't + * adjust symbols correctly in that case: */ + if (saved_shdrs != NULL && *saved_shdrs == NULL) + goto out_elf_end; + sec = elf_section_by_name(elf, &ehdr, &shdr, ".symtab", NULL); if (sec == NULL) { if (want_symtab) @@ -1031,6 +1161,9 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name, goto out_elf_end; }
+ if (saved_shdrs != NULL && *saved_shdrs == NULL) + goto out_elf_end; + opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx); if (opdsec) opddata = elf_rawdata(opdsec, NULL); @@ -1153,12 +1286,25 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name, goto new_symbol; }
+ /* + * Currently, symbols for shared objects and PIE executables + * (i.e., ET_DYN) do not seem to get adjusted. This might need + * to change if file offset == virtual address is not actually + * guaranteed for these images. ELF doesn't provide this + * guarantee natively. + */ if (curr_dso->adjust_symbols) { pr_debug4("%s: adjusting symbol: st_value: %#Lx " "sh_addr: %#Lx sh_offset: %#Lx\n", __func__, (u64)sym.st_value, (u64)shdr.sh_addr, (u64)shdr.sh_offset); - sym.st_value -= shdr.sh_addr - shdr.sh_offset; + if (saved_shdrs && *saved_shdrs && + sym.st_shndx < *saved_shdrs_count) + sym.st_value -= + (*saved_shdrs)[sym.st_shndx].sh_addr - + (*saved_shdrs)[sym.st_shndx].sh_offset; + else + sym.st_value -= shdr.sh_addr - shdr.sh_offset; } /* * We need to figure out if the object was created from C++ sources @@ -1395,6 +1541,8 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) struct machine *machine; const char *root_dir; int want_symtab; + GElf_Shdr *saved_shdrs = NULL; + unsigned saved_shdrs_count;
dso__set_loaded(self, map->type);
@@ -1425,13 +1573,13 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) * On the first pass, only load images if they have a full symtab. * Failing that, do a second pass where we accept .dynsym also */ - for (self->origin = DSO__ORIG_BUILD_ID_CACHE, want_symtab = 1; - self->origin != DSO__ORIG_NOT_FOUND; - self->origin++) { + self->origin = DSO__ORIG_BUILD_ID_CACHE; + want_symtab = 1; + while (1) { switch (self->origin) { case DSO__ORIG_BUILD_ID_CACHE: if (dso__build_id_filename(self, name, size) == NULL) - continue; + goto continue_next; break; case DSO__ORIG_FEDORA: snprintf(name, size, "/usr/lib/debug%s.debug", @@ -1445,7 +1593,7 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) char build_id_hex[BUILD_ID_SIZE * 2 + 1];
if (!self->has_build_id) - continue; + goto continue_next;
build_id__sprintf(self->build_id, sizeof(self->build_id), @@ -1469,21 +1617,24 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) default: /* * If we wanted a full symtab but no image had one, - * relax our requirements and repeat the search. + * relax our requirements and repeat the search, + * providing we saw some valid section headers: */ - if (want_symtab) { + if (want_symtab && saved_shdrs != NULL) { want_symtab = 0; self->origin = DSO__ORIG_BUILD_ID_CACHE; - } else continue; + } else + goto done; }
/* Name is now the name of the next image to try */ fd = open(name, O_RDONLY); if (fd < 0) - continue; + goto continue_next;
ret = dso__load_sym(self, map, name, fd, filter, 0, + &saved_shdrs, &saved_shdrs_count, want_symtab); close(fd);
@@ -1492,7 +1643,7 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) * info!?!? */ if (!ret) - continue; + goto continue_next;
if (ret > 0) { int nr_plt = dso__synthesize_plt_symbols(self, map, filter); @@ -1500,9 +1651,18 @@ int dso__load(struct dso *self, struct map *map, symbol_filter_t filter) ret += nr_plt; break; } + +continue_next: + self->origin++; + continue; }
+done: free(name); + + if (saved_shdrs) + free(saved_shdrs); + if (ret < 0 && strstr(self->name, " (deleted)") != NULL) return 0; return ret; @@ -1768,7 +1928,8 @@ static int dso__load_vmlinux(struct dso *self, struct map *map, return -1;
dso__set_loaded(self, map->type); - err = dso__load_sym(self, map, vmlinux, fd, filter, 0, 0); + err = dso__load_sym(self, map, vmlinux, fd, filter, 0, + NULL, NULL, 0); close(fd);
if (err > 0)