perf symbols: Implement poor man's ELF parser

Implement a minimal elf parser for getting build-id.  It assumes that
required elf.h header is provided by libc header on the system and the
parser only looks for PT_NOTE program header to check build-id.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344228082-15569-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 235 insertions, 7 deletions

diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index 416ecf3bccf5..bd8720b6780c 100644
--- a/tools/perf/util/symbol-minimal.c
+++ b/tools/perf/util/symbol-minimal.c
@@ -1,15 +1,71 @@
 #include "symbol.h"
 
+#include <elf.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <string.h>
+#include <byteswap.h>
+#include <sys/stat.h>
 
-int filename__read_build_id(const char *filename __used, void *bf __used,
-                            size_t size __used)
+
+static bool check_need_swap(int file_endian)
 {
-        return -1;
+        const int data = 1;
+        u8 *check = (u8 *)&data;
+        int host_endian;
+
+        if (check[0] == 1)
+                host_endian = ELFDATA2LSB;
+        else
+                host_endian = ELFDATA2MSB;
+
+        return host_endian != file_endian;
 }
 
-int sysfs__read_build_id(const char *filename __used, void *build_id __used,
-                         size_t size __used)
+#define NOTE_ALIGN(sz) (((sz) + 3) & ~3)
+
+#define NT_GNU_BUILD_ID 3
+
+static int read_build_id(void *note_data, size_t note_len, void *bf,
+                         size_t size, bool need_swap)
 {
+        struct {
+                u32 n_namesz;
+                u32 n_descsz;
+                u32 n_type;
+        } *nhdr;
+        void *ptr;
+
+        ptr = note_data;
+        while (ptr < (note_data + note_len)) {
+                const char *name;
+                size_t namesz, descsz;
+
+                nhdr = ptr;
+                if (need_swap) {
+                        nhdr->n_namesz = bswap_32(nhdr->n_namesz);
+                        nhdr->n_descsz = bswap_32(nhdr->n_descsz);
+                        nhdr->n_type = bswap_32(nhdr->n_type);
+                }
+
+                namesz = NOTE_ALIGN(nhdr->n_namesz);
+                descsz = NOTE_ALIGN(nhdr->n_descsz);
+
+                ptr += sizeof(*nhdr);
+                name = ptr;
+                ptr += namesz;
+                if (nhdr->n_type == NT_GNU_BUILD_ID &&
+                    nhdr->n_namesz == sizeof("GNU")) {
+                        if (memcmp(name, "GNU", sizeof("GNU")) == 0) {
+                                size_t sz = min(size, descsz);
+                                memcpy(bf, ptr, sz);
+                                memset(bf + sz, 0, size - sz);
+                                return 0;
+                        }
+                }
+                ptr += descsz;
+        }
+
         return -1;
 }
 
@@ -19,6 +75,172 @@ int filename__read_debuglink(const char *filename __used,
         return -1;
 }
 
+/*
+ * Just try PT_NOTE header otherwise fails
+ */
+int filename__read_build_id(const char *filename, void *bf, size_t size)
+{
+        FILE *fp;
+        int ret = -1;
+        bool need_swap = false;
+        u8 e_ident[EI_NIDENT];
+        size_t buf_size;
+        void *buf;
+        int i;
+
+        fp = fopen(filename, "r");
+        if (fp == NULL)
+                return -1;
+
+        if (fread(e_ident, sizeof(e_ident), 1, fp) != 1)
+                goto out;
+
+        if (memcmp(e_ident, ELFMAG, SELFMAG) ||
+            e_ident[EI_VERSION] != EV_CURRENT)
+                goto out;
+
+        need_swap = check_need_swap(e_ident[EI_DATA]);
+
+        /* for simplicity */
+        fseek(fp, 0, SEEK_SET);
+
+        if (e_ident[EI_CLASS] == ELFCLASS32) {
+                Elf32_Ehdr ehdr;
+                Elf32_Phdr *phdr;
+
+                if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1)
+                        goto out;
+
+                if (need_swap) {
+                        ehdr.e_phoff = bswap_32(ehdr.e_phoff);
+                        ehdr.e_phentsize = bswap_16(ehdr.e_phentsize);
+                        ehdr.e_phnum = bswap_16(ehdr.e_phnum);
+                }
+
+                buf_size = ehdr.e_phentsize * ehdr.e_phnum;
+                buf = malloc(buf_size);
+                if (buf == NULL)
+                        goto out;
+
+                fseek(fp, ehdr.e_phoff, SEEK_SET);
+                if (fread(buf, buf_size, 1, fp) != 1)
+                        goto out_free;
+
+                for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
+                        void *tmp;
+
+                        if (need_swap) {
+                                phdr->p_type = bswap_32(phdr->p_type);
+                                phdr->p_offset = bswap_32(phdr->p_offset);
+                                phdr->p_filesz = bswap_32(phdr->p_filesz);
+                        }
+
+                        if (phdr->p_type != PT_NOTE)
+                                continue;
+
+                        buf_size = phdr->p_filesz;
+                        tmp = realloc(buf, buf_size);
+                        if (tmp == NULL)
+                                goto out_free;
+
+                        buf = tmp;
+                        fseek(fp, phdr->p_offset, SEEK_SET);
+                        if (fread(buf, buf_size, 1, fp) != 1)
+                                goto out_free;
+
+                        ret = read_build_id(buf, buf_size, bf, size, need_swap);
+                        if (ret == 0)
+                                ret = size;
+                        break;
+                }
+        } else {
+                Elf64_Ehdr ehdr;
+                Elf64_Phdr *phdr;
+
+                if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1)
+                        goto out;
+
+                if (need_swap) {
+                        ehdr.e_phoff = bswap_64(ehdr.e_phoff);
+                        ehdr.e_phentsize = bswap_16(ehdr.e_phentsize);
+                        ehdr.e_phnum = bswap_16(ehdr.e_phnum);
+                }
+
+                buf_size = ehdr.e_phentsize * ehdr.e_phnum;
+                buf = malloc(buf_size);
+                if (buf == NULL)
+                        goto out;
+
+                fseek(fp, ehdr.e_phoff, SEEK_SET);
+                if (fread(buf, buf_size, 1, fp) != 1)
+                        goto out_free;
+
+                for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
+                        void *tmp;
+
+                        if (need_swap) {
+                                phdr->p_type = bswap_32(phdr->p_type);
+                                phdr->p_offset = bswap_64(phdr->p_offset);
+                                phdr->p_filesz = bswap_64(phdr->p_filesz);
+                        }
+
+                        if (phdr->p_type != PT_NOTE)
+                                continue;
+
+                        buf_size = phdr->p_filesz;
+                        tmp = realloc(buf, buf_size);
+                        if (tmp == NULL)
+                                goto out_free;
+
+                        buf = tmp;
+                        fseek(fp, phdr->p_offset, SEEK_SET);
+                        if (fread(buf, buf_size, 1, fp) != 1)
+                                goto out_free;
+
+                        ret = read_build_id(buf, buf_size, bf, size, need_swap);
+                        if (ret == 0)
+                                ret = size;
+                        break;
+                }
+        }
+out_free:
+        free(buf);
+out:
+        fclose(fp);
+        return ret;
+}
+
+int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
+{
+        int fd;
+        int ret = -1;
+        struct stat stbuf;
+        size_t buf_size;
+        void *buf;
+
+        fd = open(filename, O_RDONLY);
+        if (fd < 0)
+                return -1;
+
+        if (fstat(fd, &stbuf) < 0)
+                goto out;
+
+        buf_size = stbuf.st_size;
+        buf = malloc(buf_size);
+        if (buf == NULL)
+                goto out;
+
+        if (read(fd, buf, buf_size) != (ssize_t) buf_size)
+                goto out_free;
+
+        ret = read_build_id(buf, buf_size, build_id, size, false);
+out_free:
+        free(buf);
+out:
+        close(fd);
+        return ret;
+}
+
 int dso__synthesize_plt_symbols(struct dso *dso __used, char *name __used,
                                 struct map *map __used,
                                 symbol_filter_t filter __used)
@@ -26,11 +248,17 @@ int dso__synthesize_plt_symbols(struct dso *dso __used, char *name __used,
         return 0;
 }
 
-int dso__load_sym(struct dso *dso __used, struct map *map __used,
-                  const char *name __used, int fd __used,
+int dso__load_sym(struct dso *dso, struct map *map __used,
+                  const char *name, int fd __used,
                   symbol_filter_t filter __used, int kmodule __used,
                   int want_symtab __used)
 {
+        unsigned char *build_id[BUILD_ID_SIZE];
+
+        if (filename__read_build_id(name, build_id, BUILD_ID_SIZE) > 0) {
+                dso__set_build_id(dso, build_id);
+                return 1;
+        }
         return 0;
 }