elf: Detect if Elf is PIE

It is not sufficient to determine whether Elf is ET_DYN or not to be a
dynamic library in bcc_elf_is_shared_obj() function, because the executable
Elf of the PIE type is also ET_DYN.

For example, on Fedora 41, /usr/bin/bash is PIE:

    $ readelf -h /usr/bin/bash
    ELF Header:
      ...
      Type:                     DYN (Position-Independent Executable file)
      ...

bcc_elf_is_shared_obj() should not return 'true' for /usr/bin/bash.

This commit add function bcc_elf_is_pie() and export it in bcc_elf.h.

At the same time, fix test py_test_usdt3.

Signed-off-by: Rong Tao <[email protected]>
Signed-off-by: Jiang Guirong <[email protected]>

src/cc/bcc_elf.c

@@ -1013,12 +1013,52 @@ int bcc_elf_get_type(const char *path) {
     return hdr.e_type;
 }
 
+int bcc_elf_is_pie(const char *path) {
+  int i, j, res;
+  struct bcc_elf_file elf_file;
+
+  if (bcc_elf_file_open(path, &elf_file) < 0)
+    return false;
+
+  Elf *elf = elf_file.elf;
+  size_t shdrnum;
+
+  elf_getshdrnum(elf, &shdrnum);
+  res = false;
+
+  for (i = 0; i < shdrnum; i++) {
+    Elf_Scn *scn = elf_getscn(elf, i);
+    Elf64_Shdr *shdr = elf64_getshdr(scn);
+    Elf_Data *data = elf_getdata(scn, NULL);
+
+    if (shdr->sh_type != SHT_DYNAMIC)
+      continue;
+
+    Elf64_Dyn *dyns = data->d_buf;
+    for (j = 0; j * shdr->sh_entsize < shdr->sh_size; j++) {
+      Elf64_Dyn *dyn = &dyns[j];
+      if (dyn->d_tag == DT_FLAGS_1) {
+        if (dyn->d_un.d_val & DF_1_PIE) {
+          res = true;
+          goto done;
+        }
+      }
+    }
+  }
+
+done:
+  bcc_elf_file_close(&elf_file);
+  return res;
+}
+
 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 is_dyn = bcc_elf_get_type(path) == ET_DYN;
+  int is_pie = bcc_elf_is_pie(path);
+  return is_dyn ? (is_pie ? false : true) : false;
 }
 
 int bcc_elf_is_vdso(const char *name) {

src/cc/bcc_elf.h

@@ -77,6 +77,7 @@ int bcc_elf_get_text_scn_info(const char *path, uint64_t *addr,
                               uint64_t *offset);
 
 int bcc_elf_get_type(const char *path);
+int bcc_elf_is_pie(const char *path);
 int bcc_elf_is_shared_obj(const char *path);
 int bcc_elf_is_exe(const char *path);
 int bcc_elf_is_vdso(const char *name);

src/cc/usdt/usdt.cc

@@ -78,7 +78,7 @@ bool Probe::in_shared_object(const std::string &bin_path) {
 
 bool Probe::resolve_global_address(uint64_t *global, const std::string &bin_path,
                                    const uint64_t addr) {
-  if (in_shared_object(bin_path)) {
+  if (in_shared_object(bin_path) || bcc_elf_is_pie(bin_path.c_str())) {
     return (pid_ &&
             !bcc_resolve_global_addr(*pid_, bin_path.c_str(), addr, mod_match_inode_only_, global));
   }

src/cc/usdt/usdt_args.cc

@@ -58,7 +58,8 @@ bool Argument::get_global_address(uint64_t *address, const std::string &binpath,
         .resolve_name(binpath.c_str(), deref_ident_->c_str(), address);
   }
 
-  if (!bcc_elf_is_shared_obj(binpath.c_str())) {
+  if (!bcc_elf_is_shared_obj(binpath.c_str()) ||
+      bcc_elf_is_pie(binpath.c_str())) {
     struct bcc_symbol sym;
     if (bcc_resolve_symname(binpath.c_str(), deref_ident_->c_str(), 0x0, -1, nullptr, &sym) == 0) {
       *address = sym.offset;