Revert "[profile] Use base+vaddr for __llvm_write_binary_ids note pointers …"

This reverts commit 667e1fa.

Author: petrhosek

compiler-rt/lib/profile/InstrProfilingPlatformLinux.c

@@ -194,33 +194,41 @@ static int WriteBinaryIds(ProfDataWriter *Writer, const ElfW(Nhdr) * Note,
  */
 COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
   extern const ElfW(Ehdr) __ehdr_start __attribute__((visibility("hidden")));
-  extern ElfW(Dyn) _DYNAMIC[] __attribute__((weak, visibility("hidden")));
-
   const ElfW(Ehdr) *ElfHeader = &__ehdr_start;
   const ElfW(Phdr) *ProgramHeader =
       (const ElfW(Phdr) *)((uintptr_t)ElfHeader + ElfHeader->e_phoff);
 
-  /* Compute the added base address in case of position-independent code. */
-  uintptr_t Base = 0;
-  for (uint32_t I = 0; I < ElfHeader->e_phnum; I++) {
-    if (ProgramHeader[I].p_type == PT_PHDR)
-      Base = (uintptr_t)ProgramHeader - ProgramHeader[I].p_vaddr;
-    if (ProgramHeader[I].p_type == PT_DYNAMIC && _DYNAMIC)
-      Base = (uintptr_t)_DYNAMIC - ProgramHeader[I].p_vaddr;
-  }
-
   int TotalBinaryIdsSize = 0;
+  uint32_t I;
   /* Iterate through entries in the program header. */
-  for (uint32_t I = 0; I < ElfHeader->e_phnum; I++) {
+  for (I = 0; I < ElfHeader->e_phnum; I++) {
     /* Look for the notes segment in program header entries. */
     if (ProgramHeader[I].p_type != PT_NOTE)
       continue;
 
     /* There can be multiple notes segment, and examine each of them. */
-    const ElfW(Nhdr) *Note =
-        (const ElfW(Nhdr) *)(Base + ProgramHeader[I].p_vaddr);
-    const ElfW(Nhdr) *NotesEnd =
-        (const ElfW(Nhdr) *)((const char *)(Note) + ProgramHeader[I].p_memsz);
+    const ElfW(Nhdr) * Note;
+    const ElfW(Nhdr) * NotesEnd;
+    /*
+     * When examining notes in file, use p_offset, which is the offset within
+     * the elf file, to find the start of notes.
+     */
+    if (ProgramHeader[I].p_memsz == 0 ||
+        ProgramHeader[I].p_memsz == ProgramHeader[I].p_filesz) {
+      Note = (const ElfW(Nhdr) *)((uintptr_t)ElfHeader +
+                                  ProgramHeader[I].p_offset);
+      NotesEnd = (const ElfW(Nhdr) *)((const char *)(Note) +
+                                      ProgramHeader[I].p_filesz);
+    } else {
+      /*
+       * When examining notes in memory, use p_vaddr, which is the address of
+       * section after loaded to memory, to find the start of notes.
+       */
+      Note =
+          (const ElfW(Nhdr) *)((uintptr_t)ElfHeader + ProgramHeader[I].p_vaddr);
+      NotesEnd =
+          (const ElfW(Nhdr) *)((const char *)(Note) + ProgramHeader[I].p_memsz);
+    }
 
     int BinaryIdsSize = WriteBinaryIds(Writer, Note, NotesEnd);
     if (TotalBinaryIdsSize == -1)