Re: [PATCH] libstdc++: Add error handler for <stacktrace>

[Jonathan Wakely <jwakely@redhat.com>]

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On Wed, 30 Nov 2022 at 06:04, François Dumont via Libstdc++ <
libstdc++@gcc.gnu.org> wrote:

> Good catch, then we also need this patch.
>

Is it worth printing an error? If we can't show the backtrace because of an
error, we can just print nothing there.

We also need to pass an error handler to the
__glibcxx_backtrace_create_state call in formatter.h.

Now that I look at this code again, why do we need the _M_backtrace_full
member? It's always set to the same thing, why can't we just call that
function directly?

And I think we should use threaded=1 for the
__glibcxx_backtrace_create_state call.

So like the attached patch.

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commit b1ab3ca54c58e9e5505929b58bd311aca4458cda
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Nov 30 11:48:35 2022

    libstdc++: Pass error handler to libbacktrace functions
    
    Also remove a redundant data member, which also allows removing several
    namespace scope declarations.
    
    libstdc++-v3/ChangeLog:
    
            * include/debug/formatter.h [_GLIBCXX_DEBUG_BACKTRACE]
            (_Error_formatter::_Error_formatter): Pass error handler to
            __glibcxx_backtrace_create_state.
            (_Error_formatter::_M_backtrace_full): Remove data member.
            (_Error_formatter::_S_err): Define empty function.
            * src/c++11/debug.cc (_Error_formatter::_M_error): Call
            __glibcxx_backtrace_full directly.

diff --git a/libstdc++-v3/include/debug/formatter.h b/libstdc++-v3/include/debug/formatter.h
index f120163c6d4..2dd90bdf23b 100644
--- a/libstdc++-v3/include/debug/formatter.h
+++ b/libstdc++-v3/include/debug/formatter.h
@@ -32,34 +32,11 @@
 #include <bits/c++config.h>
 
 #if _GLIBCXX_HAVE_STACKTRACE
-struct __glibcxx_backtrace_state;
-
 extern "C"
-{
-  __glibcxx_backtrace_state*
-  __glibcxx_backtrace_create_state(const char*, int,
-				   void(*)(void*, const char*, int),
-				   void*);
-
-  typedef int (*__glibcxx_backtrace_full_callback) (
-    void*, __UINTPTR_TYPE__, const char *, int, const char*);
-
-  typedef void (*__glibcxx_backtrace_error_callback) (
-    void*, const char*, int);
-
-  typedef int (*__glibcxx_backtrace_full_func) (
-    __glibcxx_backtrace_state*, int,
-    __glibcxx_backtrace_full_callback,
-    __glibcxx_backtrace_error_callback,
-    void*);
-
-  int
-  __glibcxx_backtrace_full(
-    __glibcxx_backtrace_state*, int,
-    __glibcxx_backtrace_full_callback,
-    __glibcxx_backtrace_error_callback,
-    void*);
-}
+struct __glibcxx_backtrace_state*
+__glibcxx_backtrace_create_state(const char*, int,
+				 void(*)(void*, const char*, int),
+				 void*);
 #endif
 
 #if __cpp_rtti
@@ -609,8 +586,7 @@ namespace __gnu_debug
     , _M_function(__function)
 #if _GLIBCXX_HAVE_STACKTRACE
 # ifdef _GLIBCXX_DEBUG_BACKTRACE
-    , _M_backtrace_state(__glibcxx_backtrace_create_state(0, 0, 0, 0))
-    , _M_backtrace_full(&__glibcxx_backtrace_full)
+    , _M_backtrace_state(__glibcxx_backtrace_create_state(0, 1, _S_err, 0))
 # else
     , _M_backtrace_state()
 # endif
@@ -632,7 +608,8 @@ namespace __gnu_debug
     const char*		_M_function;
 #if _GLIBCXX_HAVE_STACKTRACE
     __glibcxx_backtrace_state*		_M_backtrace_state;
-    __glibcxx_backtrace_full_func	_M_backtrace_full;
+
+    static void _S_err(void*, const char*, int) { }
 #endif
 
   public:
diff --git a/libstdc++-v3/src/c++11/debug.cc b/libstdc++-v3/src/c++11/debug.cc
index 9eda38023f7..2f273ec2c93 100644
--- a/libstdc++-v3/src/c++11/debug.cc
+++ b/libstdc++-v3/src/c++11/debug.cc
@@ -1084,6 +1084,20 @@ namespace
   { print_string(ctx, str, nbc, nullptr, 0); }
 
 #if _GLIBCXX_HAVE_STACKTRACE
+extern "C"
+{
+  using __glibcxx_backtrace_full_callback
+    = int (*)(void*, __UINTPTR_TYPE__, const char *, int, const char*);
+
+  using __glibcxx_backtrace_error_callback = void (*)(void*, const char*, int);
+
+  int
+  __glibcxx_backtrace_full(__glibcxx_backtrace_state*, int,
+			   __glibcxx_backtrace_full_callback,
+			   __glibcxx_backtrace_error_callback,
+			   void*);
+}
+
   void
   print_raw(PrintContext& ctx, const char* str, ptrdiff_t nbc)
   {
@@ -1192,8 +1206,8 @@ namespace __gnu_debug
     if (_M_backtrace_state)
       {
 	print_literal(ctx, "Backtrace:\n");
-	_M_backtrace_full(
-	  _M_backtrace_state, 1, print_backtrace, nullptr, &ctx);
+	__glibcxx_backtrace_full(
+	  _M_backtrace_state, 1, print_backtrace, _S_err, &ctx);
 	ctx._M_first_line = true;
 	print_literal(ctx, "\n");
       }