[compiler-rt][profile] Add padding after binary IDs

[leonardchan]

Summary

Some tests with binary IDs would fail with error: no profile can be merged. This is because raw profiles could have unaligned headers when emitting binary IDs. This means padding should be emitted after binary IDs are emitted to ensure everything else is aligned. This patch accounts for that padding in __llvm_write_binary_ids.

[phosek]

Is this ready for review?

[leonardchan]

In D110188#3014296, @phosek wrote:

Is this ready for review?

Yup, ready now.

[phosek]

compiler-rt/lib/profile/InstrProfilingPlatformLinux.c

171

Since WriteBinaryIds isn't used from anywhere else, I'd just combine the two functions.

[phosek]

LGTM

[gulfem]

Thanks for the fix @leonardchan
Other type of paddings are added in:
https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/profile/InstrProfilingBuffer.c#L86

Do you think we can follow the same pattern?

[leonardchan]

In D110188#3016917, @gulfem wrote:

Thanks for the fix @leonardchan
Other type of paddings are added in:
https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/profile/InstrProfilingBuffer.c#L86

Do you think we can follow the same pattern?

That could work, but I think that would mean needing to call __llvm_profile_get_padding_sizes_for_counters after each instance we call __llvm_write_binary_ids when we instead could just pack it in __llvm_write_binary_ids. I imagine this is much simpler.

[nemanjai]

This appears to have broken PPC bots:
https://lab.llvm.org/buildbot/#/builders/105/builds/15291
https://lab.llvm.org/buildbot/#/builders/121/builds/11749

If you don't have an easy fix, please revert.

[leonardchan]

In D110188#3019334, @nemanjai wrote:

This appears to have broken PPC bots:
https://lab.llvm.org/buildbot/#/builders/105/builds/15291
https://lab.llvm.org/buildbot/#/builders/121/builds/11749

If you don't have an easy fix, please revert.

I have a fix up at https://reviews.llvm.org/D110365 but it looks like it's not ready to land yet. Feel free to revert it now if you can. I'm not at my keyboard right now.

compiler-rt/lib/profile/InstrProfilingPlatformLinux.c

while (Note < NotesEnd) {
     size_t NoteOffset = sizeof(ElfW(Nhdr)) + RoundUp(Note->n_namesz, 4) +
                         RoundUp(Note->n_descsz, 4);
     Note = (const ElfW(Nhdr) *)((const char *)(Note) + NoteOffset);
   }
 
   return TotalBinaryIdsSize;
 }
 
+/**
+ * Helper function that writes binary ids into profiles, but also takes into
+ * account padding after the ids to ensure the next section is 8-byte aligned.
+ * If an error happens while writing, return -1.
+ */
+static int WriteBinaryIdsWithPadding(ProfDataWriter *Writer, const ElfW(Nhdr) * Note,
+                                     const ElfW(Nhdr) * NotesEnd) {
+  int BinaryIdsSize = WriteBinaryIds(Writer, Note, NotesEnd);
+  if (BinaryIdsSize == -1)
+    return -1;
+
+  uint8_t BinaryIdsPadding = __llvm_profile_get_num_padding_bytes(BinaryIdsSize);
+  if (Writer) {
+    ProfDataIOVec BinaryIdIOVec[] = {
+        {NULL, sizeof(uint8_t), BinaryIdsPadding, 1}
+    };
+    if (Writer->Write(Writer, BinaryIdIOVec, sizeof(BinaryIdIOVec) / sizeof(*BinaryIdIOVec)))
+      return -1;
+  }
+
+  return BinaryIdsSize + BinaryIdsPadding;
+}
+
 /*
  * Write binary ids into profiles if writer is given.
  * Return the total size of binary ids.
  * If an error happens while writing, return -1.
  */
 COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
   extern const ElfW(Ehdr) __ehdr_start __attribute__((visibility("hidden")));
   const ElfW(Ehdr) *ElfHeader = &__ehdr_start;
   const ElfW(Phdr) *ProgramHeader =
       (const ElfW(Phdr) *)((uintptr_t)ElfHeader + ElfHeader->e_phoff);
 
   uint32_t I;
   /* Iterate through entries in the program header. */
   for (I = 0; I < ElfHeader->e_phnum; I++) {
     /* Look for the notes section in program header entries. */
     if (ProgramHeader[I].p_type != PT_NOTE)
       continue;
 
     const ElfW(Nhdr) *Note =
         (const ElfW(Nhdr) *)((uintptr_t)ElfHeader + ProgramHeader[I].p_offset);
     const ElfW(Nhdr) *NotesEnd =
         (const ElfW(Nhdr) *)((const char *)(Note) + ProgramHeader[I].p_filesz);
-    return WriteBinaryIds(Writer, Note, NotesEnd);
+    return WriteBinaryIdsWithPadding(Writer, Note, NotesEnd);
   }
 
   return 0;
 }
 #else /* !NT_GNU_BUILD_ID */
 /*
  * Fallback implementation for targets that don't support the GNU
  * extensions NT_GNU_BUILD_ID and __ehdr_start.
  */
 COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
   return 0;
 }
 #endif
 
 #endif