Merge pull request iovisor#1357 from palmtenor/load_section

Fix edge case when doing symbol name -> address resolution

src/cc/bcc_elf.c

@@ -470,40 +470,39 @@ int bcc_elf_foreach_sym(const char *path, bcc_elf_symcb callback,
  path, callback, (struct bcc_symbol_option*)option, payload, 0);
 }
 
-static int loadaddr(Elf *e, uint64_t *addr) {
- size_t phnum, i;
+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 (elf_getphdrnum(e, &phnum) != 0)
- return -1;
+ if (openelf(path, &e, &fd) < 0)
+ goto exit;
 
- for (i = 0; i < phnum; ++i) {
- GElf_Phdr header;
+ 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)
+ if (header.p_type != PT_LOAD || !(header.p_flags & PF_X))
  continue;
-
- *addr = (uint64_t)header.p_vaddr;
- return 0;
+ res = callback(header.p_vaddr, header.p_memsz, header.p_offset, payload);
+ if (res < 0) {
+ err = 1;
+ goto exit;
+ }
  }
+ err = 0;
 
- return -1;
-}
-
-int bcc_elf_loadaddr(const char *path, uint64_t *address) {
- Elf *e;
- int fd, res;
-
- if (openelf(path, &e, &fd) < 0)
- return -1;
-
- res = loadaddr(e, address);
- elf_end(e);
- close(fd);
-
- return res;
+exit:
+ if (e)
+ elf_end(e);
+ if (fd >= 0)
+ close(fd);
+ return err;
 }
 
 int bcc_elf_get_type(const char *path) {

src/cc/bcc_elf.h

@@ -32,17 +32,31 @@ struct bcc_elf_usdt {
  const char *arg_fmt;
 };
 
+// Binary module path, bcc_elf_usdt struct, payload
 typedef void (*bcc_elf_probecb)(const char *, const struct bcc_elf_usdt *,
  void *);
-
 // Symbol name, start address, length, payload
+// Callback returning a negative value indicates to stop the iteration
 typedef int (*bcc_elf_symcb)(const char *, uint64_t, uint64_t, void *);
+// Segment virtual address, memory size, file offset, payload
+// Callback returning a negative value indicates to stop the iteration
+typedef int (*bcc_elf_load_sectioncb)(uint64_t, uint64_t, uint64_t, void *);
 
+// Iterate over all USDT probes noted in a binary module
+// Returns -1 on error, and 0 on success
 int bcc_elf_foreach_usdt(const char *path, bcc_elf_probecb callback,
  void *payload);
-int bcc_elf_loadaddr(const char *path, uint64_t *address);
-int bcc_elf_foreach_sym(const char *path, bcc_elf_symcb callback,
- void *option, void *payload);
+// Iterate over all executable load sections of an ELF
+// Returns -1 on error, 1 if stopped by callback, and 0 on success
+int bcc_elf_foreach_load_section(const char *path,
+ bcc_elf_load_sectioncb callback,
+ void *payload);
+// Iterate over symbol table of a binary module
+// Parameter "option" points to a bcc_symbol_option struct to indicate wheather
+// and how to use debuginfo file, and what types of symbols to load.
+// Returns -1 on error, and 0 on success or stopped by callback
+int bcc_elf_foreach_sym(const char *path, bcc_elf_symcb callback, void *option,
+ void *payload);
 
 int bcc_elf_get_type(const char *path);
 int bcc_elf_is_shared_obj(const char *path);

src/cc/bcc_syms.cc

@@ -416,11 +416,24 @@ static int _find_sym(const char *symname, uint64_t addr, uint64_t,
  return 0;
 }
 
+struct load_addr_t {
+ uint64_t target_addr;
+ uint64_t binary_addr;
+};
+int _find_load(uint64_t v_addr, uint64_t mem_sz, uint64_t file_offset,
+ void *payload) {
+ struct load_addr_t *addr = static_cast<load_addr_t *>(payload);
+ if (addr->target_addr >= v_addr && addr->target_addr < (v_addr + mem_sz)) {
+ addr->binary_addr = addr->target_addr - v_addr + file_offset;
+ return -1;
+ }
+ return 0;
+}
+
 int bcc_resolve_symname(const char *module, const char *symname,
  const uint64_t addr, int pid,
  struct bcc_symbol_option *option,
  struct bcc_symbol *sym) {
- uint64_t load_addr;
  static struct bcc_symbol_option default_option = {
  .use_debug_file = 1,
  .check_debug_file_crc = 1,
@@ -437,29 +450,37 @@ int bcc_resolve_symname(const char *module, const char *symname,
  } else {
  sym->module = bcc_procutils_which_so(module, pid);
  }
-
  if (sym->module == NULL)
  return -1;
 
  ProcMountNSGuard g(pid);
 
- if (bcc_elf_loadaddr(sym->module, &load_addr) < 0)
- goto invalid_module;
-
  sym->name = symname;
  sym->offset = addr;
-
  if (option == NULL)
  option = &default_option;
 
  if (sym->name && sym->offset == 0x0)
  if (bcc_elf_foreach_sym(sym->module, _find_sym, option, sym) < 0)
  goto invalid_module;
-
  if (sym->offset == 0x0)
  goto invalid_module;
 
- sym->offset = (sym->offset - load_addr);
+ // For executable (ET_EXEC) binaries, translate the virtual address
+ // to physical address in the binary file.
+ // For shared object binaries (ET_DYN), the address from symbol table should
+ // already be physical address in the binary file.
+ if (bcc_elf_get_type(sym->module) == ET_EXEC) {
+ struct load_addr_t addr = {
+ .target_addr = sym->offset,
+ .binary_addr = 0x0,
+ };
+ if (bcc_elf_foreach_load_section(sym->module, &_find_load, &addr) < 0)
+ goto invalid_module;
+ if (!addr.binary_addr)
+ goto invalid_module;
+ sym->offset = addr.binary_addr;
+ }
  return 0;
 
 invalid_module: