Allow Java's ELF symtab reader to use separate debuginfo files
Kelly O'Hair
Kelly.Ohair at Sun.COM
Wed Dec 9 09:25:45 PST 2009
Andrew John Hughes wrote:
> 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.
Is there some other way than baking in 256 hex constants into our sources?
Why can't this logic be in a system include file somwehere?
-kto
>
>>
>> 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);
>>
>>
>>
>
>
>
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