6932270: Allow Java's ELF symtab reader to use separate debuginfo files

Reviewed-by: never
Contributed-by: Andrew Haley <aph@redhat.com>

3 files changed, 322 insertions, 6 deletions

diff --git a/agent/src/os/linux/libproc_impl.c b/agent/src/os/linux/libproc_impl.c
index be00178f2..ace53bcc3 100644
--- a/agent/src/os/linux/libproc_impl.c
+++ b/agent/src/os/linux/libproc_impl.c
@@ -174,7 +174,7 @@ lib_info* add_lib_info_fd(struct ps_prochandle* ph, const char* libname, int fd,
       return NULL;
    }
 
-   newlib->symtab = build_symtab(newlib->fd);
+   newlib->symtab = build_symtab(newlib->fd, libname);
    if (newlib->symtab == NULL) {
       print_debug("symbol table build failed for %s\n", newlib->name);
    }
diff --git a/agent/src/os/linux/symtab.c b/agent/src/os/linux/symtab.c
index ec3b99ff3..d135a3333 100644
--- a/agent/src/os/linux/symtab.c
+++ b/agent/src/os/linux/symtab.c
@@ -53,8 +53,274 @@ typedef struct symtab {
   struct hsearch_data *hash_table;
 } symtab_t;
 
-// read symbol table from given fd.
-struct symtab* build_symtab(int fd) {
+
+// Directory that contains global debuginfo files.  In theory it
+// should be possible to change this, but in a Java environment there
+// is no obvious place to put a user interface to do it.  Maybe this
+// could be set with an environment variable.
+static const char debug_file_directory[] = "/usr/lib/debug";
+
+/* The CRC used in gnu_debuglink, retrieved from
+   http://sourceware.org/gdb/current/onlinedocs/gdb/Separate-Debug-Files.html#Separate-Debug-Files. */
+unsigned int gnu_debuglink_crc32 (unsigned int crc,
+                                  unsigned char *buf, size_t len)
+{
+  static const unsigned int crc32_table[256] =
+    {
+      0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
+      0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
+      0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
+      0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
+      0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
+      0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
+      0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
+      0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
+      0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
+      0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
+      0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
+      0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+      0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
+      0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
+      0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
+      0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
+      0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
+      0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
+      0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
+      0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
+      0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
+      0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
+      0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
+      0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+      0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
+      0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
+      0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
+      0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
+      0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
+      0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
+      0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
+      0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
+      0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
+      0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
+      0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
+      0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+      0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
+      0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
+      0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
+      0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
+      0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
+      0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
+      0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
+      0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
+      0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
+      0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
+      0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
+      0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+      0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
+      0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
+      0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
+      0x2d02ef8d
+    };
+  unsigned char *end;
+
+  crc = ~crc & 0xffffffff;
+  for (end = buf + len; buf < end; ++buf)
+    crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
+  return ~crc & 0xffffffff;
+}
+
+/* Open a debuginfo file and check its CRC.  If it exists and the CRC
+   matches return its fd.  */
+static int
+open_debug_file (const char *pathname, unsigned int crc)
+{
+  unsigned int file_crc = 0;
+  unsigned char buffer[8 * 1024];
+
+  int fd = pathmap_open(pathname);
+
+  if (fd < 0)
+    return -1;
+
+  lseek(fd, 0, SEEK_SET);
+
+  for (;;) {
+    int len = read(fd, buffer, sizeof buffer);
+    if (len <= 0)
+      break;
+    file_crc = gnu_debuglink_crc32(file_crc, buffer, len);
+  }
+
+  if (crc == file_crc)
+    return fd;
+  else {
+    close(fd);
+    return -1;
+  }
+}
+
+/* Find an ELF section.  */
+static struct elf_section *find_section_by_name(char *name,
+                                                int fd,
+                                                ELF_EHDR *ehdr,
+                                                ELF_SHDR *shbuf,
+                                                struct elf_section *scn_cache)
+{
+  ELF_SHDR* cursct = NULL;
+  char *strtab;
+  int cnt;
+
+  if (scn_cache[ehdr->e_shstrndx].c_data == NULL) {
+    if ((scn_cache[ehdr->e_shstrndx].c_data
+         = read_section_data(fd, ehdr, cursct)) == NULL) {
+      return NULL;
+    }
+  }
+
+  strtab = scn_cache[ehdr->e_shstrndx].c_data;
+
+  for (cursct = shbuf, cnt = 0;
+       cnt < ehdr->e_shnum;
+       cnt++, cursct++) {
+    if (strcmp(cursct->sh_name + strtab, name) == 0) {
+      scn_cache[cnt].c_data = read_section_data(fd, ehdr, cursct);
+      return &scn_cache[cnt];
+    }
+  }
+
+  return NULL;
+}
+
+/* Look for a ".gnu_debuglink" section.  If one exists, try to open a
+   suitable debuginfo file.  */
+static int open_file_from_debug_link(const char *name,
+                                     int fd,
+                                     ELF_EHDR *ehdr,
+                                     ELF_SHDR *shbuf,
+                                     struct elf_section *scn_cache)
+{
+  int debug_fd;
+  struct elf_section *debug_link = find_section_by_name(".gnu_debuglink", fd, ehdr,
+                                                        shbuf, scn_cache);
+  if (debug_link == NULL)
+    return -1;
+  char *debug_filename = debug_link->c_data;
+  int offset = (strlen(debug_filename) + 4) >> 2;
+  static unsigned int crc;
+  crc = ((unsigned int*)debug_link->c_data)[offset];
+  char *debug_pathname = malloc(strlen(debug_filename)
+                                + strlen(name)
+                                + strlen(".debug/")
+                                + strlen(debug_file_directory)
+                                + 2);
+  strcpy(debug_pathname, name);
+  char *last_slash = strrchr(debug_pathname, '/');
+  if (last_slash == NULL)
+    return -1;
+
+  /* Look in the same directory as the object.  */
+  strcpy(last_slash+1, debug_filename);
+
+  debug_fd = open_debug_file(debug_pathname, crc);
+  if (debug_fd >= 0) {
+    free(debug_pathname);
+    return debug_fd;
+  }
+
+  /* Look in a subdirectory named ".debug".  */
+  strcpy(last_slash+1, ".debug/");
+  strcat(last_slash, debug_filename);
+
+  debug_fd = open_debug_file(debug_pathname, crc);
+  if (debug_fd >= 0) {
+    free(debug_pathname);
+    return debug_fd;
+  }
+
+  /* Look in /usr/lib/debug + the full pathname.  */
+  strcpy(debug_pathname, debug_file_directory);
+  strcat(debug_pathname, name);
+  last_slash = strrchr(debug_pathname, '/');
+  strcpy(last_slash+1, debug_filename);
+
+  debug_fd = open_debug_file(debug_pathname, crc);
+  if (debug_fd >= 0) {
+    free(debug_pathname);
+    return debug_fd;
+  }
+
+  free(debug_pathname);
+  return -1;
+}
+
+static struct symtab* build_symtab_internal(int fd, const char *filename, bool try_debuginfo);
+
+/* Look for a ".gnu_debuglink" section.  If one exists, try to open a
+   suitable debuginfo file and read a symbol table from it.  */
+static struct symtab *build_symtab_from_debug_link(const char *name,
+                                     int fd,
+                                     ELF_EHDR *ehdr,
+                                     ELF_SHDR *shbuf,
+                                     struct elf_section *scn_cache)
+{
+  fd = open_file_from_debug_link(name, fd, ehdr, shbuf, scn_cache);
+
+  if (fd >= 0) {
+    struct symtab *symtab = build_symtab_internal(fd, NULL, /* try_debuginfo */ false);
+    close(fd);
+    return symtab;
+  }
+
+  return NULL;
+}
+
+// Given a build_id, find the associated debuginfo file
+static char *
+build_id_to_debug_filename (size_t size, unsigned char *data)
+{
+  char *filename, *s;
+
+  filename = malloc(strlen (debug_file_directory) + (sizeof "/.build-id/" - 1) + 1
+                    + 2 * size + (sizeof ".debug" - 1) + 1);
+  s = filename + sprintf (filename, "%s/.build-id/", debug_file_directory);
+  if (size > 0)
+    {
+      size--;
+      s += sprintf (s, "%02x", *data++);
+    }
+  if (size > 0)
+    *s++ = '/';
+  while (size-- > 0)
+    s += sprintf (s, "%02x", *data++);
+  strcpy (s, ".debug");
+
+  return filename;
+}
+
+// Read a build ID note.  Try to open any associated debuginfo file
+// and return its symtab
+static struct symtab* build_symtab_from_build_id(Elf64_Nhdr *note)
+{
+  int fd;
+  struct symtab *symtab = NULL;
+
+  unsigned char *bytes
+    = (unsigned char*)(note+1) + note->n_namesz;
+  unsigned char *filename
+    = (build_id_to_debug_filename (note->n_descsz, bytes));
+
+  fd = pathmap_open(filename);
+  if (fd >= 0) {
+    symtab = build_symtab_internal(fd, NULL, /* try_debuginfo */ false);
+    close(fd);
+  }
+  free(filename);
+
+  return symtab;
+}
+
+// read symbol table from given fd.  If try_debuginfo) is true, also
+// try to open an associated debuginfo file
+static struct symtab* build_symtab_internal(int fd, const char *filename, bool try_debuginfo) {
   ELF_EHDR ehdr;
   char *names = NULL;
   struct symtab* symtab = NULL;
@@ -66,6 +332,7 @@ struct symtab* build_symtab(int fd) {
   ELF_SHDR* cursct = NULL;
   ELF_PHDR* phbuf = NULL;
   ELF_PHDR* phdr = NULL;
+  int sym_section = SHT_DYNSYM;
 
   uintptr_t baseaddr = (uintptr_t)-1;
 
@@ -90,18 +357,23 @@ struct symtab* build_symtab(int fd) {
 
   for (cursct = shbuf, cnt = 0; cnt < ehdr.e_shnum; cnt++) {
     scn_cache[cnt].c_shdr = cursct;
-    if (cursct->sh_type == SHT_SYMTAB || cursct->sh_type == SHT_STRTAB) {
+    if (cursct->sh_type == SHT_SYMTAB || cursct->sh_type == SHT_STRTAB
+        || cursct->sh_type == SHT_NOTE || cursct->sh_type == SHT_DYNSYM) {
       if ( (scn_cache[cnt].c_data = read_section_data(fd, &ehdr, cursct)) == NULL) {
          goto quit;
       }
     }
+    if (cursct->sh_type == SHT_SYMTAB) {
+      // Full symbol table available so use that
+      sym_section = cursct->sh_type;
+    }
     cursct++;
   }
 
   for (cnt = 1; cnt < ehdr.e_shnum; cnt++) {
     ELF_SHDR *shdr = scn_cache[cnt].c_shdr;
 
-    if (shdr->sh_type == SHT_SYMTAB) {
+    if (shdr->sh_type == sym_section) {
       ELF_SYM  *syms;
       int j, n, rslt;
       size_t size;
@@ -163,6 +435,45 @@ struct symtab* build_symtab(int fd) {
     }
   }
 
+  // Look for a separate debuginfo file.
+  if (try_debuginfo) {
+
+    // We prefer a debug symtab to an object's own symtab, so look in
+    // the debuginfo file.  We stash a copy of the old symtab in case
+    // there is no debuginfo.
+    struct symtab* prev_symtab = symtab;
+    symtab = NULL;
+
+#ifdef NT_GNU_BUILD_ID
+    // First we look for a Build ID
+    for (cursct = shbuf, cnt = 0;
+         symtab == NULL && cnt < ehdr.e_shnum;
+         cnt++) {
+      if (cursct->sh_type == SHT_NOTE) {
+        Elf64_Nhdr *note = (Elf64_Nhdr *)scn_cache[cnt].c_data;
+        if (note->n_type == NT_GNU_BUILD_ID) {
+          symtab = build_symtab_from_build_id(note);
+        }
+      }
+      cursct++;
+    }
+#endif
+
+    // Then, if that doesn't work, the debug link
+    if (symtab == NULL) {
+      symtab = build_symtab_from_debug_link(filename, fd, &ehdr, shbuf,
+                                            scn_cache);
+    }
+
+    // If we still haven't found a symtab, use the object's own symtab.
+    if (symtab != NULL) {
+      if (prev_symtab != NULL)
+        destroy_symtab(prev_symtab);
+    } else {
+      symtab = prev_symtab;
+    }
+  }
+
 quit:
   if (shbuf) free(shbuf);
   if (phbuf) free(phbuf);
@@ -177,6 +488,11 @@ quit:
   return symtab;
 }
 
+struct symtab* build_symtab(int fd, const char *filename) {
+  return build_symtab_internal(fd, filename, /* try_debuginfo */ true);
+}
+
+
 void destroy_symtab(struct symtab* symtab) {
   if (!symtab) return;
   if (symtab->strs) free(symtab->strs);
diff --git a/agent/src/os/linux/symtab.h b/agent/src/os/linux/symtab.h
index 371fc7fb1..90762cb66 100644
--- a/agent/src/os/linux/symtab.h
+++ b/agent/src/os/linux/symtab.h
@@ -32,7 +32,7 @@
 struct symtab;
 
 // build symbol table for a given ELF file descriptor
-struct symtab* build_symtab(int fd);
+struct symtab* build_symtab(int fd, const char *filename);
 
 // destroy the symbol table
 void destroy_symtab(struct symtab* symtab);