[Libunwind] Fix msan-related errors

Sometimes msan seems to fail proving that
variable is (un)initialized and emits false-positives.
Such false positives can lead to stack overflow (libc++ CI error)
So add explicit initialization of all variables that
msan thinks are used without initialization

Author: chestnykh

libunwind/src/AddressSpace.hpp

@@ -621,6 +621,9 @@ inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr,
   }
   // Try to find the unwind info using `dl_find_object`
   dl_find_object findResult;
+#if __has_feature(memory_sanitizer)
+  __builtin_memset(&findResult, 0, sizeof(dl_find_object));
+#endif
   if (dlFindObject && dlFindObject((void *)targetAddr, &findResult) == 0) {
     if (findResult.dlfo_eh_frame == nullptr) {
       // Found an entry for `targetAddr`, but there is no unwind info.

libunwind/src/UnwindLevel1-gcc-ext.c

@@ -133,6 +133,10 @@ _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_Backtrace(_Unwind_Trace_Fn callback, void *ref) {
   unw_cursor_t cursor;
   unw_context_t uc;
+#if __has_feature(memory_sanitizer)
+  __builtin_memset(&cursor, 0, sizeof(cursor));
+  __builtin_memset(&uc, 0, sizeof(uc));
+#endif
   __unw_getcontext(&uc);
   __unw_init_local(&cursor, &uc);
 

libunwind/src/UnwindLevel1.c

@@ -507,6 +507,10 @@ _Unwind_ForcedUnwind(_Unwind_Exception *exception_object,
                        (void *)exception_object, (void *)(uintptr_t)stop);
   unw_context_t uc;
   unw_cursor_t cursor;
+#if __has_feature(memory_sanitizer)
+  __builtin_memset(&uc, 0, sizeof(uc));
+  __builtin_memset(&cursor, 0, sizeof(cursor));
+#endif
   __unw_getcontext(&uc);
 
   // Mark that this is a forced unwind, so _Unwind_Resume() can do

libunwind/test/libunwind_01.pass.cpp

@@ -16,10 +16,10 @@
 #include <string.h>
 
 void backtrace(int lower_bound) {
-  unw_context_t context;
+  unw_context_t context = {0};
   unw_getcontext(&context);
 
-  unw_cursor_t cursor;
+  unw_cursor_t cursor = {0};
   unw_init_local(&cursor, &context);
 
   char buffer[1024];
@@ -64,10 +64,10 @@ __attribute__((noinline)) void test3(int i, int j, int k) {
 }
 
 void test_no_info() {
-  unw_context_t context;
+  unw_context_t context = {0};
   unw_getcontext(&context);
 
-  unw_cursor_t cursor;
+  unw_cursor_t cursor = {0};
   unw_init_local(&cursor, &context);
 
   unw_proc_info_t info;
@@ -84,10 +84,10 @@ void test_no_info() {
 }
 
 void test_reg_names() {
-  unw_context_t context;
+  unw_context_t context = {0};
   unw_getcontext(&context);
 
-  unw_cursor_t cursor;
+  unw_cursor_t cursor = {0};
   unw_init_local(&cursor, &context);
 
   int max_reg_num = -100;
@@ -110,7 +110,7 @@ void test_reg_names() {
 
 #if defined(__x86_64__)
 void test_reg_get_set() {
-  unw_context_t context;
+  unw_context_t context = {0};
   unw_getcontext(&context);
 
   unw_cursor_t cursor;
@@ -131,10 +131,10 @@ void test_reg_get_set() {
 }
 
 void test_fpreg_get_set() {
-  unw_context_t context;
+  unw_context_t context = {0};
   unw_getcontext(&context);
 
-  unw_cursor_t cursor;
+  unw_cursor_t cursor = {0};
   unw_init_local(&cursor, &context);
 
   // get/set is not implemented for x86_64 fpregs.

libunwind/test/signal_frame.pass.cpp

@@ -29,8 +29,8 @@
 
 void test() {
   asm(".cfi_signal_frame");
-  unw_cursor_t cursor;
-  unw_context_t uc;
+  unw_cursor_t cursor = {0};
+  unw_context_t uc = {0};
   unw_getcontext(&uc);
   unw_init_local(&cursor, &uc);
   assert(unw_step(&cursor) > 0);

libunwind/test/unw_resume.pass.cpp

@@ -13,8 +13,8 @@
 #include <libunwind.h>
 
 __attribute__((noinline)) void test_unw_resume() {
-  unw_context_t context;
-  unw_cursor_t cursor;
+  unw_context_t context = {0};
+  unw_cursor_t cursor = {0};
 
   unw_getcontext(&context);
   unw_init_local(&cursor, &context);