[asan,test] Make alloca_loop_unpoisoning.cpp robust and fix s390x failure

[MaskRay]

In the test from https://reviews.llvm.org/D7098, char array[len]; is
32-byte aligned on most targets whether it is instrumented or not
(optimized by StackSafetyAnalysis), due to the the used *FrameLowering
being StackRealignable.

However, when using SystemZELFFrameLowering, an un-instrumented
char array[len]; is only 8-byte aligned.

Ensure char array[len]; gets instrumented like what we did to
alloca_vla_interact.cpp, to make the test pass on s390x.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Fangrui Song (MaskRay)

Changes

In the test from https://reviews.llvm.org/D7098, char array[len]; is
32-byte aligned on most targets whether it is instrumented or not
(optimized by StackSafetyAnalysis), due to the the used *FrameLowering
being StackRealignable.

However, when using SystemZELFFrameLowering, an un-instrumented
char array[len]; is only 8-byte aligned.

Ensure char array[len]; gets instrumented like what we did to
alloca_vla_interact.cpp, to make the test pass on s390x.

---

Full diff: https://github.com/llvm/llvm-project/pull/78774.diff

1 Files Affected:

• (modified) compiler-rt/test/asan/TestCases/alloca_loop_unpoisoning.cpp (+4-3)

diff --git a/compiler-rt/test/asan/TestCases/alloca_loop_unpoisoning.cpp b/compiler-rt/test/asan/TestCases/alloca_loop_unpoisoning.cpp
index ac25a4faa2dc1b..bf84ab3d20d7de 100644
--- a/compiler-rt/test/asan/TestCases/alloca_loop_unpoisoning.cpp
+++ b/compiler-rt/test/asan/TestCases/alloca_loop_unpoisoning.cpp
@@ -2,7 +2,6 @@
 // RUN: %env_asan_opts=detect_stack_use_after_return=0 %run %t 2>&1
 //
 // REQUIRES: stable-runtime
-// UNSUPPORTED: target=s390{{.*}}
 
 // This testcase checks that allocas and VLAs inside loop are correctly unpoisoned.
 
@@ -25,11 +24,13 @@ void *top, *bot;
 __attribute__((noinline)) void foo(int len) {
   char x;
   top = &x;
-  char array[len];
+  volatile char array[len];
+  if (len) array[0] = 0;
   assert(!(reinterpret_cast<uintptr_t>(array) & 31L));
   alloca(len);
   for (int i = 0; i < 32; ++i) {
-    char array[i];
+    volatile char array[i];
+    if (i) array[0] = 0;
     bot = alloca(i);
     assert(!(reinterpret_cast<uintptr_t>(bot) & 31L));
   }

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[uweigand]

Yes, this works for me on SystemZ. LGTM, thanks!