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bcc_elf.c
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bcc_elf.c
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/*
* Copyright (c) 2016 GitHub, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http:https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#ifdef HAVE_LIBDEBUGINFOD
#include <elfutils/debuginfod.h>
#endif
#include <gelf.h>
#include "bcc_elf.h"
#include "bcc_proc.h"
#include "bcc_syms.h"
#define NT_STAPSDT 3
#define ELF_ST_TYPE(x) (((uint32_t) x) & 0xf)
static int openelf_fd(int fd, Elf **elf_out) {
if (elf_version(EV_CURRENT) == EV_NONE)
return -1;
*elf_out = elf_begin(fd, ELF_C_READ, 0);
if (*elf_out == NULL)
return -1;
return 0;
}
static int openelf(const char *path, Elf **elf_out, int *fd_out) {
*fd_out = open(path, O_RDONLY);
if (*fd_out < 0)
return -1;
if (openelf_fd(*fd_out, elf_out) == -1) {
close(*fd_out);
return -1;
}
return 0;
}
static const char *parse_stapsdt_note(struct bcc_elf_usdt *probe,
GElf_Shdr *probes_shdr,
const char *desc, int elf_class) {
if (elf_class == ELFCLASS32) {
probe->pc = *((uint32_t *)(desc));
probe->base_addr = *((uint32_t *)(desc + 4));
probe->semaphore = *((uint32_t *)(desc + 8));
desc = desc + 12;
} else {
probe->pc = *((uint64_t *)(desc));
probe->base_addr = *((uint64_t *)(desc + 8));
probe->semaphore = *((uint64_t *)(desc + 16));
desc = desc + 24;
}
// Offset from start of file
if (probe->semaphore && probes_shdr)
probe->semaphore_offset =
probe->semaphore - probes_shdr->sh_addr + probes_shdr->sh_offset;
else
probe->semaphore_offset = 0;
probe->provider = desc;
desc += strlen(desc) + 1;
probe->name = desc;
desc += strlen(desc) + 1;
probe->arg_fmt = desc;
desc += strlen(desc) + 1;
return desc;
}
static int do_note_segment(Elf_Scn *section, GElf_Shdr *probes_shdr, int elf_class,
bcc_elf_probecb callback, const char *binpath,
uint64_t first_inst_offset, void *payload) {
Elf_Data *data = NULL;
while ((data = elf_getdata(section, data)) != 0) {
size_t offset = 0;
GElf_Nhdr hdr;
size_t name_off, desc_off;
while ((offset = gelf_getnote(data, offset, &hdr, &name_off, &desc_off)) !=
0) {
const char *desc, *desc_end;
struct bcc_elf_usdt probe;
if (hdr.n_type != NT_STAPSDT)
continue;
if (hdr.n_namesz != 8)
continue;
if (memcmp((const char *)data->d_buf + name_off, "stapsdt", 8) != 0)
continue;
desc = (const char *)data->d_buf + desc_off;
desc_end = desc + hdr.n_descsz;
if (parse_stapsdt_note(&probe, probes_shdr, desc, elf_class) == desc_end) {
if (probe.pc < first_inst_offset)
fprintf(stderr,
"WARNING: invalid address 0x%lx for probe (%s,%s) in binary %s\n",
probe.pc, probe.provider, probe.name, binpath);
else
callback(binpath, &probe, payload);
}
}
}
return 0;
}
static int listprobes(Elf *e, bcc_elf_probecb callback, const char *binpath,
void *payload) {
Elf_Scn *section = NULL;
bool found_probes_shdr;
size_t stridx;
int elf_class = gelf_getclass(e);
uint64_t first_inst_offset = 0;
GElf_Shdr probes_shdr = {};
if (elf_getshdrstrndx(e, &stridx) != 0)
return -1;
// Get the offset to the first instruction
while ((section = elf_nextscn(e, section)) != 0) {
GElf_Shdr header;
if (!gelf_getshdr(section, &header))
continue;
// The elf file section layout is based on increasing virtual address,
// getting the first section with SHF_EXECINSTR is enough.
if (header.sh_flags & SHF_EXECINSTR) {
first_inst_offset = header.sh_addr;
break;
}
}
found_probes_shdr = false;
while ((section = elf_nextscn(e, section)) != 0) {
if (!gelf_getshdr(section, &probes_shdr))
continue;
char *name = elf_strptr(e, stridx, probes_shdr.sh_name);
if (name && !strcmp(name, ".probes")) {
found_probes_shdr = true;
break;
}
}
while ((section = elf_nextscn(e, section)) != 0) {
GElf_Shdr header;
char *name;
if (!gelf_getshdr(section, &header))
continue;
if (header.sh_type != SHT_NOTE)
continue;
name = elf_strptr(e, stridx, header.sh_name);
if (name && !strcmp(name, ".note.stapsdt")) {
GElf_Shdr *shdr_ptr = found_probes_shdr ? &probes_shdr : NULL;
if (do_note_segment(section, shdr_ptr, elf_class, callback, binpath,
first_inst_offset, payload) < 0)
return -1;
}
}
return 0;
}
int bcc_elf_foreach_usdt(const char *path, bcc_elf_probecb callback,
void *payload) {
Elf *e;
int fd, res;
if (openelf(path, &e, &fd) < 0)
return -1;
res = listprobes(e, callback, path, payload);
elf_end(e);
close(fd);
return res;
}
static Elf_Scn * get_section(Elf *e, const char *section_name,
GElf_Shdr *section_hdr, size_t *section_idx) {
Elf_Scn *section = NULL;
GElf_Shdr header;
char *name;
size_t stridx;
if (elf_getshdrstrndx(e, &stridx) != 0)
return NULL;
size_t index;
for (index = 1; (section = elf_nextscn(e, section)) != 0; index++) {
if (!gelf_getshdr(section, &header))
continue;
name = elf_strptr(e, stridx, header.sh_name);
if (name && !strcmp(name, section_name)) {
if (section_hdr)
*section_hdr = header;
if (section_idx)
*section_idx = index;
return section;
}
}
return NULL;
}
static int list_in_scn(Elf *e, Elf_Scn *section, size_t stridx, size_t symsize,
struct bcc_symbol_option *option,
bcc_elf_symcb callback, bcc_elf_symcb_lazy callback_lazy,
void *payload, bool debugfile) {
Elf_Data *data = NULL;
#if defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
size_t opdidx = 0;
Elf_Scn *opdsec = NULL;
GElf_Shdr opdshdr = {};
Elf_Data *opddata = NULL;
opdsec = get_section(e, ".opd", &opdshdr, &opdidx);
if (opdsec && opdshdr.sh_type == SHT_PROGBITS)
opddata = elf_getdata(opdsec, NULL);
#endif
while ((data = elf_getdata(section, data)) != 0) {
size_t i, symcount = data->d_size / symsize;
if (data->d_size % symsize)
return -1;
for (i = 0; i < symcount; ++i) {
GElf_Sym sym;
const char *name;
size_t name_len;
if (!gelf_getsym(data, (int)i, &sym))
continue;
if ((name = elf_strptr(e, stridx, sym.st_name)) == NULL)
continue;
if (name[0] == 0)
continue;
name_len = strlen(name);
if (sym.st_value == 0)
continue;
uint32_t st_type = ELF_ST_TYPE(sym.st_info);
if (!(option->use_symbol_type & (1 << st_type)))
continue;
#ifdef __powerpc64__
#if defined(_CALL_ELF) && _CALL_ELF == 2
if (option->use_symbol_type & (1 << STT_PPC64_ELFV2_SYM_LEP)) {
/*
* The PowerPC 64-bit ELF v2 ABI says that the 3 most significant bits
* in the st_other field of the symbol table specifies the number of
* instructions between a function's Global Entry Point (GEP) and Local
* Entry Point (LEP).
*/
switch (sym.st_other >> 5) {
/* GEP and LEP are the same for 0 or 1, usage is reserved for 7 */
/* If 2, LEP is 1 instruction past the GEP */
case 2: sym.st_value += 4; break;
/* If 3, LEP is 2 instructions past the GEP */
case 3: sym.st_value += 8; break;
/* If 4, LEP is 4 instructions past the GEP */
case 4: sym.st_value += 16; break;
/* If 5, LEP is 8 instructions past the GEP */
case 5: sym.st_value += 32; break;
/* If 6, LEP is 16 instructions past the GEP */
case 6: sym.st_value += 64; break;
}
}
#else
if (opddata && sym.st_shndx == opdidx) {
size_t offset = sym.st_value - opdshdr.sh_addr;
/* Find the function descriptor */
uint64_t *descr = opddata->d_buf + offset;
/* Read the actual entry point address from the descriptor */
sym.st_value = *descr;
}
#endif
#endif
int ret;
if (option->lazy_symbolize)
ret = callback_lazy(stridx, sym.st_name, name_len, sym.st_value,
sym.st_size, debugfile, payload);
else
ret = callback(name, sym.st_value, sym.st_size, payload);
if (ret < 0)
return 1; // signal termination to caller
}
}
return 0;
}
static int listsymbols(Elf *e, bcc_elf_symcb callback,
bcc_elf_symcb_lazy callback_lazy, void *payload,
struct bcc_symbol_option *option, bool debugfile) {
Elf_Scn *section = NULL;
while ((section = elf_nextscn(e, section)) != 0) {
GElf_Shdr header;
if (!gelf_getshdr(section, &header))
continue;
if (header.sh_type != SHT_SYMTAB && header.sh_type != SHT_DYNSYM)
continue;
int rc = list_in_scn(e, section, header.sh_link, header.sh_entsize,
option, callback, callback_lazy, payload, debugfile);
if (rc == 1)
break; // callback signaled termination
if (rc < 0)
return rc;
}
return 0;
}
static Elf_Data * get_section_elf_data(Elf *e, const char *section_name) {
Elf_Scn *section = get_section(e, section_name, NULL, NULL);
if (section)
return elf_getdata(section, NULL);
return NULL;
}
static int find_debuglink(Elf *e, char **debug_file, unsigned int *crc) {
Elf_Data *data = NULL;
*debug_file = NULL;
*crc = 0;
data = get_section_elf_data(e, ".gnu_debuglink");
if (!data || data->d_size <= 5)
return 0;
*debug_file = (char *)data->d_buf;
*crc = *(unsigned int*)((char *)data->d_buf + data->d_size - 4);
return *debug_file ? 1 : 0;
}
static int find_buildid(Elf *e, char *buildid) {
Elf_Data *data = get_section_elf_data(e, ".note.gnu.build-id");
if (!data || data->d_size <= 16 || strcmp((char *)data->d_buf + 12, "GNU"))
return 0;
char *buf = (char *)data->d_buf + 16;
size_t length = data->d_size - 16;
size_t i = 0;
for (i = 0; i < length; ++i) {
sprintf(buildid + (i * 2), "%02hhx", buf[i]);
}
return 1;
}
// The CRC algorithm used by GNU debuglink. Taken from:
// https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html
static unsigned int gnu_debuglink_crc32(unsigned int crc,
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
};
char *end;
crc = ~crc & 0xffffffff;
for (end = buf + len; buf < end; ++buf)
crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
return ~crc & 0xffffffff;
}
static int verify_checksum(const char *file, unsigned int crc) {
struct stat st;
int fd;
void *buf;
unsigned int actual;
fd = open(file, O_RDONLY);
if (fd < 0)
return 0;
if (fstat(fd, &st) < 0) {
close(fd);
return 0;
}
buf = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
if (!buf) {
close(fd);
return 0;
}
actual = gnu_debuglink_crc32(0, buf, st.st_size);
munmap(buf, st.st_size);
close(fd);
return actual == crc;
}
// Check if two filenames point to the same file, including hard or soft links.
static bool same_file(char *a, const char *b)
{
struct stat stat_a, stat_b;
if (stat(a, &stat_a) || stat(b, &stat_b))
return false;
if ((stat_a.st_dev == stat_b.st_dev) &&
(stat_a.st_ino == stat_b.st_ino))
return true;
else
return false;
}
static char *find_debug_via_debuglink(Elf *e, const char *binpath,
int check_crc) {
char fullpath[PATH_MAX];
char *tmppath;
char *bindir = NULL;
char *res = NULL;
unsigned int crc;
char *name; // the name of the debuginfo file
if (!find_debuglink(e, &name, &crc))
return NULL;
tmppath = strdup(binpath);
bindir = dirname(tmppath);
// Search for the file in 'binpath', but ignore the file we find if it
// matches the binary itself: the binary will always be probed later on,
// and it might contain poorer symbols (e.g. stripped or partial symbols)
// than the external debuginfo that might be available elsewhere.
snprintf(fullpath, sizeof(fullpath),"%s/%s", bindir, name);
if (same_file(fullpath, binpath) != true && access(fullpath, F_OK) != -1) {
res = strdup(fullpath);
goto DONE;
}
// Search for the file in 'binpath'/.debug
snprintf(fullpath, sizeof(fullpath), "%s/.debug/%s", bindir, name);
if (access(fullpath, F_OK) != -1) {
res = strdup(fullpath);
goto DONE;
}
// Search for the file in the global debug directory /usr/lib/debug/'binpath'
snprintf(fullpath, sizeof(fullpath), "/usr/lib/debug%s/%s", bindir, name);
if (access(fullpath, F_OK) != -1) {
res = strdup(fullpath);
goto DONE;
}
DONE:
free(tmppath);
if (res && check_crc && !verify_checksum(res, crc)) {
free(res);
return NULL;
}
return res;
}
static char *find_debug_via_buildid(Elf *e) {
char fullpath[PATH_MAX];
char buildid[128]; // currently 40 seems to be default, let's be safe
if (!find_buildid(e, buildid))
return NULL;
// Search for the file in the global debug directory with a sub-path:
// mm/nnnnnn...nnnn.debug
// Where mm are the first two characters of the buildid, and nnnn are the
// rest of the build id, followed by .debug.
snprintf(fullpath, sizeof(fullpath), "/usr/lib/debug/.build-id/%c%c/%s.debug",
buildid[0], buildid[1], buildid + 2);
if (access(fullpath, F_OK) != -1) {
return strdup(fullpath);
}
return NULL;
}
static char *find_debug_via_symfs(Elf *e, const char* path) {
char fullpath[PATH_MAX];
char buildid[128];
char symfs_buildid[128];
int check_build_id;
char *symfs;
Elf *symfs_e = NULL;
int symfs_fd = -1;
char *result = NULL;
symfs = getenv("BCC_SYMFS");
if (!symfs || !*symfs)
goto out;
check_build_id = find_buildid(e, buildid);
int ns_prefix_length = 0;
sscanf(path, "/proc/%*u/root/%n", &ns_prefix_length);
path += ns_prefix_length;
snprintf(fullpath, sizeof(fullpath), "%s/%s", symfs, path);
if (access(fullpath, F_OK) == -1)
goto out;
if (openelf(fullpath, &symfs_e, &symfs_fd) < 0) {
symfs_e = NULL;
symfs_fd = -1;
goto out;
}
if (check_build_id) {
if (!find_buildid(symfs_e, symfs_buildid))
goto out;
if (strncmp(buildid, symfs_buildid, sizeof(buildid)))
goto out;
}
result = strdup(fullpath);
out:
if (symfs_e) {
elf_end(symfs_e);
}
if (symfs_fd != -1) {
close(symfs_fd);
}
return result;
}
#ifdef HAVE_LIBDEBUGINFOD
static char *find_debug_via_debuginfod(Elf *e){
char buildid[128];
char *debugpath = NULL;
int fd = -1;
if (!find_buildid(e, buildid))
return NULL;
debuginfod_client *client = debuginfod_begin();
if (!client)
return NULL;
// In case of an error, the function returns a negative error code and
// debugpath stays NULL.
fd = debuginfod_find_debuginfo(client, (const unsigned char *) buildid, 0,
&debugpath);
if (fd >= 0)
close(fd);
debuginfod_end(client);
return debugpath;
}
#endif
static char *find_debug_file(Elf* e, const char* path, int check_crc) {
char *debug_file = NULL;
// If there is a separate debuginfo file, try to locate and read it, first
// using symfs, then using the build-id section, finally using the debuglink
// section. These rules are what perf and gdb follow.
// See:
// - https://github.com/torvalds/linux/blob/v5.2/tools/perf/Documentation/perf-report.txt#L325
// - https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html
debug_file = find_debug_via_symfs(e, path);
if (!debug_file)
debug_file = find_debug_via_buildid(e);
if (!debug_file)
debug_file = find_debug_via_debuglink(e, path, check_crc);
#ifdef HAVE_LIBDEBUGINFOD
if (!debug_file)
debug_file = find_debug_via_debuginfod(e);
#endif
return debug_file;
}
static int foreach_sym_core(const char *path, bcc_elf_symcb callback,
bcc_elf_symcb_lazy callback_lazy,
struct bcc_symbol_option *option, void *payload,
int is_debug_file) {
Elf *e;
int fd, res;
char *debug_file;
if (!option)
return -1;
if (openelf(path, &e, &fd) < 0)
return -1;
if (option->use_debug_file && !is_debug_file) {
// The is_debug_file argument helps avoid infinitely resolving debuginfo
// files for debuginfo files and so on.
debug_file = find_debug_file(e, path,
option->check_debug_file_crc);
if (debug_file) {
foreach_sym_core(debug_file, callback, callback_lazy, option, payload, 1);
free(debug_file);
}
}
res = listsymbols(e, callback, callback_lazy, payload, option, is_debug_file);
elf_end(e);
close(fd);
return res;
}
int bcc_elf_foreach_sym(const char *path, bcc_elf_symcb callback,
void *option, void *payload) {
struct bcc_symbol_option *o = option;
o->lazy_symbolize = 0;
return foreach_sym_core(path, callback, NULL, o, payload, 0);
}
int bcc_elf_foreach_sym_lazy(const char *path, bcc_elf_symcb_lazy callback,
void *option, void *payload) {
struct bcc_symbol_option *o = option;
o->lazy_symbolize = 1;
return foreach_sym_core(path, NULL, callback, o, payload, 0);
}
int bcc_elf_get_text_scn_info(const char *path, uint64_t *addr,
uint64_t *offset) {
Elf *e = NULL;
int fd = -1, err;
Elf_Scn *section = NULL;
GElf_Shdr header;
size_t stridx;
char *name;
if ((err = openelf(path, &e, &fd)) < 0 ||
(err = elf_getshdrstrndx(e, &stridx)) < 0)
goto exit;
err = -1;
while ((section = elf_nextscn(e, section)) != 0) {
if (!gelf_getshdr(section, &header))
continue;
name = elf_strptr(e, stridx, header.sh_name);
if (name && !strcmp(name, ".text")) {
*addr = (uint64_t)header.sh_addr;
*offset = (uint64_t)header.sh_offset;
err = 0;
break;
}
}
exit:
if (e)
elf_end(e);
if (fd >= 0)
close(fd);
return err;
}
int bcc_elf_foreach_load_section(const char *path,
bcc_elf_load_sectioncb callback,
void *payload) {
Elf *e = NULL;
int fd = -1, err = -1, res;
size_t nhdrs, i;
if (openelf(path, &e, &fd) < 0)
goto exit;
if (elf_getphdrnum(e, &nhdrs) != 0)
goto exit;
GElf_Phdr header;
for (i = 0; i < nhdrs; i++) {
if (!gelf_getphdr(e, (int)i, &header))
continue;
if (header.p_type != PT_LOAD || !(header.p_flags & PF_X))
continue;
res = callback(header.p_vaddr, header.p_memsz, header.p_offset, payload);
if (res < 0) {
err = 1;
goto exit;
}
}
err = 0;
exit:
if (e)
elf_end(e);
if (fd >= 0)
close(fd);
return err;
}
int bcc_elf_get_type(const char *path) {
Elf *e;
GElf_Ehdr hdr;
int fd;
void* res = NULL;
if (openelf(path, &e, &fd) < 0)
return -1;
res = (void*)gelf_getehdr(e, &hdr);
elf_end(e);
close(fd);
if (!res)
return -1;
else
return hdr.e_type;
}
int bcc_elf_is_exe(const char *path) {
return (bcc_elf_get_type(path) != -1) && (access(path, X_OK) == 0);
}
int bcc_elf_is_shared_obj(const char *path) {
return bcc_elf_get_type(path) == ET_DYN;
}
int bcc_elf_is_vdso(const char *name) {
return strcmp(name, "[vdso]") == 0;
}
// -2: Failed
// -1: Not initialized
// >0: Initialized
static int vdso_image_fd = -1;
static int find_vdso(struct mod_info *info, int enter_ns, void *payload) {
int fd;
char tmpfile[128];
if (!bcc_elf_is_vdso(info->name))
return 0;
uint64_t sz = info->end_addr - info->start_addr;
void *image = malloc(sz);
if (!image)
goto on_error;
memcpy(image, (void *)info->start_addr, sz);
snprintf(tmpfile, sizeof(tmpfile), "/tmp/bcc_%d_vdso_image_XXXXXX", getpid());
fd = mkostemp(tmpfile, O_CLOEXEC);
if (fd < 0) {
fprintf(stderr, "Unable to create temp file: %s\n", strerror(errno));
goto on_error;
}
// Unlink the file to avoid leaking
if (unlink(tmpfile) == -1)
fprintf(stderr, "Unlink %s failed: %s\n", tmpfile, strerror(errno));
if (write(fd, image, sz) == -1) {
fprintf(stderr, "Failed to write to vDSO image: %s\n", strerror(errno));
close(fd);
goto on_error;
}
vdso_image_fd = fd;
on_error:
if (image)
free(image);
// Always stop the iteration
return -1;
}
int bcc_elf_foreach_vdso_sym(bcc_elf_symcb callback, void *payload) {
Elf *elf;
static struct bcc_symbol_option default_option = {
.use_debug_file = 0,
.check_debug_file_crc = 0,
.use_symbol_type = (1 << STT_FUNC) | (1 << STT_GNU_IFUNC)
};
if (vdso_image_fd == -1) {
vdso_image_fd = -2;
bcc_procutils_each_module(getpid(), &find_vdso, NULL);
}
if (vdso_image_fd == -2)
return -1;
if (openelf_fd(vdso_image_fd, &elf) == -1)
return -1;
return listsymbols(elf, callback, NULL, payload, &default_option, 0);
}
// return value: 0 : success
// < 0 : error and no bcc lib found
// > 0 : error and bcc lib found
static int bcc_free_memory_with_file(const char *path) {
unsigned long sym_addr = 0, sym_shndx;
Elf_Scn *section = NULL;
int fd = -1, err;
GElf_Shdr header;
Elf *e = NULL;
if ((err = openelf(path, &e, &fd)) < 0)
goto exit;
// get symbol address of "bcc_free_memory", which
// will be used to calculate runtime .text address
// range, esp. for shared libraries.
err = -1;
while ((section = elf_nextscn(e, section)) != 0) {
Elf_Data *data = NULL;
size_t symsize;
if (!gelf_getshdr(section, &header))
continue;
if (header.sh_type != SHT_SYMTAB && header.sh_type != SHT_DYNSYM)
continue;
/* iterate all symbols */
symsize = header.sh_entsize;
while ((data = elf_getdata(section, data)) != 0) {
size_t i, symcount = data->d_size / symsize;
for (i = 0; i < symcount; ++i) {
GElf_Sym sym;
if (!gelf_getsym(data, (int)i, &sym))
continue;
if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
continue;
const char *name;
if ((name = elf_strptr(e, header.sh_link, sym.st_name)) == NULL)
continue;
if (strcmp(name, "bcc_free_memory") == 0) {
sym_addr = sym.st_value;
sym_shndx = sym.st_shndx;
break;
}
}
}
}
// Didn't find bcc_free_memory in the ELF file.
if (sym_addr == 0)
goto exit;
int sh_idx = 0;
section = NULL;
err = 1;
while ((section = elf_nextscn(e, section)) != 0) {
sh_idx++;
if (!gelf_getshdr(section, &header))
continue;
if (sh_idx == sym_shndx) {
unsigned long saddr, saddr_n, eaddr;
long page_size = sysconf(_SC_PAGESIZE);
saddr = (unsigned long)bcc_free_memory - sym_addr + header.sh_addr;
eaddr = saddr + header.sh_size;
// adjust saddr and eaddr, start addr needs to be page aligned
saddr_n = (saddr + page_size - 1) & ~(page_size - 1);
eaddr -= saddr_n - saddr;
if (madvise((void *)saddr_n, eaddr - saddr_n, MADV_DONTNEED)) {
fprintf(stderr, "madvise failed, saddr %lx, eaddr %lx\n", saddr, eaddr);
goto exit;
}
err = 0;
break;
}
}
exit:
if (e)
elf_end(e);
if (fd >= 0)
close(fd);
return err;
}
// Free bcc mmemory
//
// The main purpose of this function is to free llvm/clang text memory
// through madvise MADV_DONTNEED.
//
// bcc could be linked statically or dynamically into the application.
// If it is static linking, there is no easy way to know which region
// inside .text section belongs to llvm/clang, so the whole .text section
// is freed. Otherwise, the process map is searched to find libbcc.so
// library and the whole .text section for that shared library is
// freed.
//
// Note that the text memory used by bcc (mainly llvm/clang) is reclaimable
// in the kernel as it is file backed. But the reclaim process
// may take some time if no memory pressure. So this API is mostly
// used for application who needs to immediately lowers its RssFile
// metric right after loading BPF program.
int bcc_free_memory() {
int err;
// First try whether bcc is statically linked or not
err = bcc_free_memory_with_file("/proc/self/exe");
if (err >= 0)