[libunwind] [libunwind][AIX] Remove weak definition "__xlcxx_personality_v0" (PR #112436)

[Hubert Tong via cfe-commits]

================
@@ -2126,42 +2125,34 @@ bool UnwindCursor<A, R>::getInfoFromTBTable(pint_t pc, 
R &registers) {
     // function __xlcxx_personality_v0(), which is the personality for the 
state
     // table and is exported from libc++abi, is directly assigned as the
     // handler here. When a legacy XLC++ frame is encountered, the symbol
-    // is resolved dynamically using dlopen() to avoid hard dependency from
-    // libunwind on libc++abi.
+    // is resolved dynamically using dlopen() to avoid a hard dependency of
+    // libunwind on libc++abi in cases such as non-C++ applications.
 
     // Resolve the function pointer to the state table personality if it has
-    // not already.
+    // not already done.
     if (xlcPersonalityV0 == NULL) {
       xlcPersonalityV0InitLock.lock();
       if (xlcPersonalityV0 == NULL) {
-        // If libc++abi is statically linked in, symbol __xlcxx_personality_v0
-        // has been resolved at the link time.
-        xlcPersonalityV0 = &__xlcxx_personality_v0;
+        // Resolve __xlcxx_personality_v0 using dlopen().
+        const char libcxxabi[] = "libc++abi.a(libc++abi.so.1)";
+        void *libHandle;
+        // The AIX dlopen() sets errno to 0 when it is successful, which
+        // clobbers the value of errno from the user code. This is an AIX
+        // bug because according to POSIX it should not set errno to 0. To
+        // workaround before AIX fixes the bug, errno is saved and restored.
+        int saveErrno = errno;
+        libHandle = dlopen(libcxxabi, RTLD_MEMBER | RTLD_NOW);
+        if (libHandle == NULL) {
+          _LIBUNWIND_TRACE_UNWINDING("dlopen() failed with errno=%d\n", errno);
+          assert(0 && "dlopen() failed");
+        }
+        xlcPersonalityV0 = reinterpret_cast<__xlcxx_personality_v0_t *>(
+            dlsym(libHandle, "__xlcxx_personality_v0"));
         if (xlcPersonalityV0 == NULL) {
-          // libc++abi is dynamically linked. Resolve __xlcxx_personality_v0
-          // using dlopen().
-          const char libcxxabi[] = "libc++abi.a(libc++abi.so.1)";
-          void *libHandle;
-          // The AIX dlopen() sets errno to 0 when it is successful, which
-          // clobbers the value of errno from the user code. This is an AIX
-          // bug because according to POSIX it should not set errno to 0. To
-          // workaround before AIX fixes the bug, errno is saved and restored.
-          int saveErrno = errno;
-          libHandle = dlopen(libcxxabi, RTLD_MEMBER | RTLD_NOW);
-          if (libHandle == NULL) {
-            _LIBUNWIND_TRACE_UNWINDING("dlopen() failed with errno=%d\n",
-                                       errno);
-            assert(0 && "dlopen() failed");
-          }
-          xlcPersonalityV0 = reinterpret_cast<__xlcxx_personality_v0_t *>(
-              dlsym(libHandle, "__xlcxx_personality_v0"));
-          if (xlcPersonalityV0 == NULL) {
-            _LIBUNWIND_TRACE_UNWINDING("dlsym() failed with errno=%d\n", 
errno);
-            assert(0 && "dlsym() failed");
-          }
-          dlclose(libHandle);
----------------
hubert-reinterpretcast wrote:

I don't think the drive-by fix to remove the call to `dlclose` should be done 
in the same PR.

https://github.com/llvm/llvm-project/pull/112436
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