[test] Make Linux/sem_init_glibc.cpp robust

[MaskRay]

Summary

and fix it for 32-bit ports defining sem_init@GLIBC_2.0 (i386, mips32, powerpc32) for glibc>=2.36.

Fix https://github.com/llvm/llvm-project/issues/58079

[MaskRay]

fix a comment typo

[MaskRay]

blind mips64 fix

[MaskRay]

actually fix mips64

[mgorny]

I can confirm that this fixes the problem for me on amd64 (with i386 multilib). I have also confirmed that the patched version works on arm64 with both glibc 2.35 and 2.36.

compiler-rt/test/sanitizer_common/TestCases/Linux/sem_init_glibc.cpp

 // RUN: %clangxx -O0 -g %s -lutil -o %t && %run %t
 // This test depends on the glibc layout of struct sem_t and checks that we
 // don't leave sem_t::private uninitialized.
-// UNSUPPORTED: android, lsan-x86, ubsan, target-is-mips64, target-is-mips64el
+// UNSUPPORTED: android, lsan-x86, ubsan
 #include <features.h>
 #include <assert.h>
 #include <semaphore.h>
 #include <string.h>
 #include <stdint.h>
 
-// On powerpc64be semval_t must be 64 bits even with "old" versions of glibc.
-#if __PPC64__ && __BIG_ENDIAN__
-typedef uint64_t semval_t;
-
-// This condition needs to correspond to __HAVE_64B_ATOMICS macro in glibc.
-#elif (defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \
-     defined(__s390x__) || defined(__sparc64__) || defined(__alpha__) || \
-     defined(__ia64__) || defined(__m68k__)) && __GLIBC_PREREQ(2, 21)
-typedef uint64_t semval_t;
-#else
+// musl, glibc's __HAVE_64B_ATOMICS==0 ports (e.g. arm, i386) and 64-bit ports
+// available before 2.1 (none supported by compiler-rt) use 32-bit sem values.
+#if !defined(__GLIBC__) || defined(__ILP32__)
 typedef unsigned semval_t;
+#else
+typedef uint64_t semval_t;
 #endif
 
-// glibc 2.21 has introduced some changes in the way the semaphore value is
-// handled for 32-bit platforms, but since these changes are not ABI-breaking
-// they are not versioned. On newer platforms such as ARM, there is only one
-// version of the symbol, so it's enough to check the glibc version. However,
-// for old platforms such as i386, glibc contains two or even three versions of
-// the sem_init symbol, and the sanitizers always pick the oldest one.
-// Therefore, it is not enough to rely on the __GLIBC_PREREQ macro - we should
-// instead check the platform as well to make sure we only expect the new
-// behavior on platforms where the older symbols do not exist.
-#if defined(__arm__) && __GLIBC_PREREQ(2, 21)
-#define GET_SEM_VALUE(V) ((V) >> 1)
+// Some glibc __HAVE_64B_ATOMICS==0 ports definition a sem_init which shifts the
+// value by 1 (https://sourceware.org/PR12674). The version is picked if either
+// glibc>=2.36 (https://sourceware.org/PR14932) or the port is available after
+// glibc 2.21 (arm and newer ports).
+//
+// The __GLIBC_PREREQ check is brittle in that it requires matched
+// __GLIBC_PREREQ values for build time and run time.
+#if defined(__GLIBC__) && defined(__ILP32__) &&                                \
+    (__GLIBC_PREREQ(2, 36) ||                                                  \
+     (__GLIBC_PREREQ(2, 21) && !defined(__i386__) && !defined(__powerpc__)))
+#  define GET_SEM_VALUE(V) ((V) >> 1)
 #else
-#define GET_SEM_VALUE(V) (V)
+#  define GET_SEM_VALUE(V) (V)
 #endif
 
 void my_sem_init(bool priv, int value, semval_t *a, unsigned char *b) {
   sem_t sem;
   memset(&sem, 0xAB, sizeof(sem));
   sem_init(&sem, priv, value);
 
   char *p = (char *)&sem;