[InstrProf][compiler-rt] Fix counter section alignment issue

[ellis]

Summary

I recently discovered that .profraw headers are expected to be 8 byte
aligned.
https://github.com/llvm/llvm-project/blob/643ba926c1f618401c86dc37e659df795db2e1a0/llvm/lib/ProfileData/InstrProfReader.cpp#L503-L506

When function entry coverage mode is used, function counters are single
bytes, so it is likely that the size of the counters section is not 8
byte aligned. We can add padding after the counters section to guarantee
this.

[kyulee]

LGTM

compiler-rt/test/profile/instrprof-entry-coverage.c

6 ↗

(On Diff #529752)

Can you add a quick comment on what you're testing here?

[gulfem]

compiler-rt/test/profile/instrprof-entry-coverage.c

6 ↗

(On Diff #529752)

I literally ran into this padding issue yesterday while I was experimenting with single byte counters for coverage. Thanks for fixing this! Instead of concatenating two raw profiles in a test to test counter section alignment, I would suggest writing a shared library test similar to https://github.com/llvm/llvm-project/blob/main/compiler-rt/test/profile/Posix/instrprof-shared.test, where profiles are concatenated under the hood. Other than that, it looks good to me.

[ellis]

Add shared library test

[ellis]

compiler-rt/test/profile/instrprof-entry-coverage.c

6 ↗

(On Diff #529752)

Thanks for the suggestion! I like this new test much better. Feel free to reach out if you find any other issues with single byte counters :)

[gulfem]

compiler-rt/test/profile/instrprof-entry-coverage.c

6 ↗

(On Diff #529752)

Sounds good!

compiler-rt/lib/profile/InstrProfilingBuffer.c

 
 COMPILER_RT_VISIBILITY
 void __llvm_profile_get_padding_sizes_for_counters(
     uint64_t DataSize, uint64_t CountersSize, uint64_t NamesSize,
     uint64_t *PaddingBytesBeforeCounters, uint64_t *PaddingBytesAfterCounters,
     uint64_t *PaddingBytesAfterNames) {
   if (!needsCounterPadding()) {
     *PaddingBytesBeforeCounters = 0;
-    *PaddingBytesAfterCounters = 0;
+    *PaddingBytesAfterCounters =
+        __llvm_profile_get_num_padding_bytes(CountersSize);
     *PaddingBytesAfterNames = __llvm_profile_get_num_padding_bytes(NamesSize);
     return;
   }
 
   // In continuous mode, the file offsets for headers and for the start of
   // counter sections need to be page-aligned.
   *PaddingBytesBeforeCounters =
       calculateBytesNeededToPageAlign(sizeof(__llvm_profile_header) + DataSize);

compiler-rt/test/profile/Posix/instrprof-shared-entry-coverage.test

+# When linking an instrumented shared libary, the produced raw profile may have
+# multiple headers which must be 8 byte aligned. Check that the counter section
+# sizes are 8 byte aligned when using function entry coverage by attempting to
+# merge the raw profile.
+
+RUN: mkdir -p %t.d
+RUN: %clang_pgogen -mllvm -pgo-function-entry-coverage -o %t.d/libfoo.so -fPIC -shared %S/../Inputs/instrprof-shared-lib.c
+RUN: %clang_pgogen -mllvm -pgo-function-entry-coverage -o %t -L%t.d -rpath %t.d -lfoo %S/../Inputs/instrprof-shared-main.c
+RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t
+RUN: llvm-profdata merge -o %t.profdata %t.profraw
+RUN: llvm-profdata show --covered %t.profdata | FileCheck %s
+
+CHECK-DAG: main
+CHECK-DAG: foo