Allow Java's ELF symtab reader to use separate debuginfo files
Andrew John Hughes
gnu_andrew at member.fsf.org
Wed Dec 9 08:26:42 PST 2009
2009/12/9 Andrew Haley <aph at redhat.com>:
> This is https://bugzilla.redhat.com/show_bug.cgi?id=541548
> The symptom is that jmap doesn't work because target libraries are stripped.
> The fix is to allow the symtab reader to use the separate debuginfo files
> that are available for all (AFAIK) GNU/Linux distributions.
>
> I'll commit this to the IcedTea repo, with a view to pushing it upstream
> to OpenJDK if it works on all distros.
>
> Andrew.
>
It would be good to see this upstream. The obvious compatibility
issue I can see is hardcoding /usr/lib/debug. Passing that in from
the Makefile, thus allowing to be overridden if necessary, might be
better.
i.e.
static const char debug_file_directory[] = "/usr/lib/debug";
becomes
#ifndef DEBUG_FILE_DIRECTORY
#define DEBUG_FILE_DIRECTORY "/usr/lib/debug"
#endif
with apppropriate logic in the OpenJDK makefile(s).
Only other comment is that your ChangeLog should refer to openjdk, not
openjdk-ecj as we want this for all builds. The patch itself is
correct, it's just the ChangeLog.
Redirecting this mail to the HotSpot and serviceability lists rather
than tl as it concerns the serviceability tools in HotSpot.
>
>
> 2009-12-09 Andrew Haley <aph at redhat.com>
>
> * openjdk-ecj/hotspot/agent/src/os/linux/symtab.c (debug_file_directory):
> New variable.
> (gnu_debuglink_crc32): New.
> (build_symtab_internal): Rename from build_symtab, make static.
> Add logic to look inside debuginfo files.
> (open_debug_file, find_section_by_name, open_file_from_debug_link,
> build_id_to_debug_filename, build_symtab_from_build_id,
> build_symtab): New.
> * openjdk-ecj/hotspot/agent/src/os/linux/libproc_impl.c (add_lib_info_fd):
> Pass FILENAME to build_symtab().
> * openjdk-ecj/hotspot/agent/src/os/linux/symtab.h (build_symtab):
> Add FILENAME arg.
>
> diff -u ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/libproc_impl.c openjdk/hotspot/agent/src/os/linux/libproc_impl.c
> --- ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/libproc_impl.c 2009-05-15 00:36:38.000000000 +0100
> +++ openjdk/hotspot/agent/src/os/linux/libproc_impl.c 2009-12-04 16:29:27.552837905 +0000
> @@ -174,7 +174,7 @@
> 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 -u ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/symtab.c openjdk/hotspot/agent/src/os/linux/symtab.c
> --- ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/symtab.c 2009-05-15 00:36:38.000000000 +0100
> +++ openjdk/hotspot/agent/src/os/linux/symtab.c 2009-12-07 13:53:13.107734342 +0000
> @@ -53,8 +53,272 @@
> 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 long gnu_debuglink_crc32 (unsigned long crc,
> + unsigned char *buf, size_t len)
> +{
> + static const unsigned long 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)
> +{
> + struct elf_section *debug_link = find_section_by_name(".gnu_debuglink", fd, ehdr,
> + shbuf, scn_cache);
> + int debug_fd;
> + char *debug_filename = debug_link->c_data;
> + int offset = strlen(debug_filename) + 3 >> 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;
> @@ -90,7 +354,8 @@
>
> 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) {
> if ( (scn_cache[cnt].c_data = read_section_data(fd, &ehdr, cursct)) == NULL) {
> goto quit;
> }
> @@ -163,6 +428,28 @@
> }
> }
>
> + // If we have no symtab in this file, look for a separate debuginfo file
> + if (try_debuginfo) {
> + // 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++;
> + }
> +
> + // Then, if that doesn't work, the debug link
> + if (symtab == NULL) {
> + symtab = build_symtab_from_debug_link(filename, fd, &ehdr, shbuf,
> + scn_cache);
> + }
> + }
> +
> quit:
> if (shbuf) free(shbuf);
> if (phbuf) free(phbuf);
> @@ -177,6 +464,11 @@
> 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 -u ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/symtab.h openjdk/hotspot/agent/src/os/linux/symtab.h
> --- ../openjdk/icedtea6/openjdk/hotspot/agent/src/os/linux/symtab.h 2009-05-15 00:36:38.000000000 +0100
> +++ openjdk/hotspot/agent/src/os/linux/symtab.h 2009-12-04 16:30:38.797838015 +0000
> @@ -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);
>
>
>
--
Andrew :-)
Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)
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