fix #32678, error due to Ptr constant in _reformat_bt (#33524)

Also change `jl_get_backtrace` to return a pair of values instead of
mutating.

Author: JeffBezanson

base/error.jl

@@ -70,7 +70,7 @@ function _reformat_bt(bt, bt2)
     i, j = 1, 1
     while i <= length(bt)
         ip = bt[i]::Ptr{Cvoid}
-        if ip == Ptr{Cvoid}(-1%UInt)
+        if UInt(ip) == (-1 % UInt)
             # The next one is really a CodeInfo
             push!(ret, InterpreterIP(
                 bt2[j],
@@ -95,8 +95,8 @@ function backtrace()
     # skip frame for backtrace(). Note that for this to work properly,
     # backtrace() itself must not be interpreted nor inlined.
     skip = 1
-    bt1, bt2 = ccall(:jl_backtrace_from_here, Any, (Cint,Cint), false, skip)
-    _reformat_bt(bt1, bt2)
+    bt1, bt2 = ccall(:jl_backtrace_from_here, Ref{SimpleVector}, (Cint, Cint), false, skip)
+    return _reformat_bt(bt1::Vector{Ptr{Cvoid}}, bt2::Vector{Any})
 end
 
 """
@@ -105,10 +105,8 @@ end
 Get the backtrace of the current exception, for use within `catch` blocks.
 """
 function catch_backtrace()
-    bt = Ref{Any}(nothing)
-    bt2 = Ref{Any}(nothing)
-    ccall(:jl_get_backtrace, Cvoid, (Ref{Any}, Ref{Any}), bt, bt2)
-    return _reformat_bt(bt[], bt2[])
+    bt, bt2 = ccall(:jl_get_backtrace, Ref{SimpleVector}, ())
+    return _reformat_bt(bt::Vector{Ptr{Cvoid}}, bt2::Vector{Any})
 end
 
 """

src/julia_internal.h

@@ -646,7 +646,7 @@ size_t rec_backtrace_ctx(uintptr_t *bt_data, size_t maxsize, bt_context_t *ctx,
 #ifdef LIBOSXUNWIND
 size_t rec_backtrace_ctx_dwarf(uintptr_t *bt_data, size_t maxsize, bt_context_t *ctx, int add_interp_frames) JL_NOTSAFEPOINT;
 #endif
-JL_DLLEXPORT void jl_get_backtrace(jl_array_t **bt, jl_array_t **bt2);
+JL_DLLEXPORT jl_value_t *jl_get_backtrace(void);
 void jl_critical_error(int sig, bt_context_t *context, uintptr_t *bt_data, size_t *bt_size);
 JL_DLLEXPORT void jl_raise_debugger(void);
 int jl_getFunctionInfo(jl_frame_t **frames, uintptr_t pointer, int skipC, int noInline) JL_NOTSAFEPOINT;

src/stackwalk.c

@@ -240,18 +240,17 @@ JL_DLLEXPORT jl_value_t *jl_backtrace_from_here(int returnsp, int skip)
     return bt;
 }
 
+// note: btout and bt2out must be GC roots
 void decode_backtrace(uintptr_t *bt_data, size_t bt_size,
                       jl_array_t **btout, jl_array_t **bt2out)
 {
-    jl_array_t *bt = NULL;
-    jl_array_t *bt2 = NULL;
-    JL_GC_PUSH2(&bt, &bt2);
+    jl_array_t *bt, *bt2;
     if (array_ptr_void_type == NULL) {
         array_ptr_void_type = jl_apply_type2((jl_value_t*)jl_array_type, (jl_value_t*)jl_voidpointer_type, jl_box_long(1));
     }
-    bt = jl_alloc_array_1d(array_ptr_void_type, bt_size);
+    bt = *btout = jl_alloc_array_1d(array_ptr_void_type, bt_size);
     memcpy(bt->data, bt_data, bt_size * sizeof(void*));
-    bt2 = jl_alloc_array_1d(jl_array_any_type, 0);
+    bt2 = *bt2out = jl_alloc_array_1d(jl_array_any_type, 0);
     // Scan the stack for any interpreter frames
     size_t n = 0;
     while (n < bt_size) {
@@ -261,12 +260,9 @@ void decode_backtrace(uintptr_t *bt_data, size_t bt_size,
         }
         n++;
     }
-    *btout = bt;
-    *bt2out = bt2;
-    JL_GC_POP();
 }
 
-JL_DLLEXPORT void jl_get_backtrace(jl_array_t **btout, jl_array_t **bt2out)
+JL_DLLEXPORT jl_value_t *jl_get_backtrace(void)
 {
     jl_excstack_t *s = jl_get_ptls_states()->current_task->excstack;
     uintptr_t *bt_data = NULL;
@@ -275,7 +271,12 @@ JL_DLLEXPORT void jl_get_backtrace(jl_array_t **btout, jl_array_t **bt2out)
         bt_data = jl_excstack_bt_data(s, s->top);
         bt_size = jl_excstack_bt_size(s, s->top);
     }
-    decode_backtrace(bt_data, bt_size, btout, bt2out);
+    jl_array_t *bt = NULL, *bt2 = NULL;
+    JL_GC_PUSH2(&bt, &bt2);
+    decode_backtrace(bt_data, bt_size, &bt, &bt2);
+    jl_svec_t *pair = jl_svec2(bt, bt2);
+    JL_GC_POP();
+    return (jl_value_t*)pair;
 }
 
 // Return data from the exception stack for `task` as an array of Any, starting