flang: fix backtrace build on FreeBSD

[brooksdavis]

FreeBSD's libexecinfo defines backtrace with a size_t for the size argument and return type. This almost certainly doesn't make sense, but what's done is done so cast the output to allow compilation. Otherwise we get:

.../flang/runtime/stop.cpp:165:13: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
165 | int nptrs{backtrace(buffer, MAX_CALL_STACK)};
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Brooks Davis (brooksdavis)

Changes

FreeBSD's libexecinfo defines backtrace with a size_t for the size argument and return type. This almost certainly doesn't make sense, but what's done is done so cast the output to allow compilation. Otherwise we get:

.../flang/runtime/stop.cpp:165:13: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
165 | int nptrs{backtrace(buffer, MAX_CALL_STACK)};
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

---

Full diff: https://github.com/llvm/llvm-project/pull/120297.diff

1 Files Affected:

• (modified) flang/runtime/stop.cpp (+1-1)

diff --git a/flang/runtime/stop.cpp b/flang/runtime/stop.cpp
index f8457e10566a23..a7be8a082e026b 100644
--- a/flang/runtime/stop.cpp
+++ b/flang/runtime/stop.cpp
@@ -162,7 +162,7 @@ static void PrintBacktrace() {
   // TODO: Need to parse DWARF information to print function line numbers
   constexpr int MAX_CALL_STACK{999};
   void *buffer[MAX_CALL_STACK];
-  int nptrs{backtrace(buffer, MAX_CALL_STACK)};
+  int nptrs{(int)backtrace(buffer, MAX_CALL_STACK)};
 
   if (char **symbols{backtrace_symbols(buffer, nptrs)}) {
     for (int i = 0; i < nptrs; i++) {

[brooksdavis]

This fixes e8baa79