Simplify _reformat_bt.

Author: maleadt

base/error.jl

@@ -65,11 +65,11 @@ struct InterpreterIP
     mod::Union{Module,Nothing}
 end
 
-# convert dual arrays (raw bt buffer, array of GC managed values) to a single
-# array of locations
-function _reformat_bt(bt, bt2)
-    ret = Vector{Union{InterpreterIP,Ptr{Cvoid}}}()
-    i, j = 1, 1
+# convert an array of raw backtrace entries to array of usable objects
+# (either native pointers or InterpreterIP objects)
+function _reformat_bt(bt)
+    ret = Vector{Union{Ptr{Cvoid},InterpreterIP}}()
+    i = 1
     while i <= length(bt)
         ip = bt[i]::Ptr{Cvoid}
         if UInt(ip) != (-1 % UInt) # See also jl_bt_is_native
@@ -85,15 +85,18 @@ function _reformat_bt(bt, bt2)
         tag       = (entry_metadata >> 6) & 0xf
         header    =  entry_metadata >> 10
         if tag == 1 # JL_BT_INTERP_FRAME_TAG
-            code = bt2[j]
-            mod = njlvalues == 2 ? bt2[j+1] : nothing
+            code = unsafe_pointer_to_objref(convert(Ptr{Any}, bt[i+2]))
+            mod = if njlvalues == 2
+                unsafe_pointer_to_objref(convert(Ptr{Any}, bt[i+3]))
+            else
+                nothing
+            end
             push!(ret, InterpreterIP(code, header, mod))
         else
             # Tags we don't know about are an error
             throw(ArgumentError("Unexpected extended backtrace entry tag $tag at bt[$i]"))
         end
         # See jl_bt_entry_size
-        j += njlvalues
         i += Int(2 + njlvalues + nuintvals)
     end
     ret
@@ -110,7 +113,10 @@ function backtrace()
     # backtrace() itself must not be interpreted nor inlined.
     skip = 1
     bt1, bt2 = ccall(:jl_backtrace_from_here, Ref{SimpleVector}, (Cint, Cint), false, skip)
-    return _reformat_bt(bt1::Vector{Ptr{Cvoid}}, bt2::Vector{Any})
+    t = @_gc_preserve_begin bt2
+    bt = _reformat_bt(bt1::Vector{Ptr{Cvoid}})
+    @_gc_preserve_end t
+    return bt
 end
 
 """
@@ -119,8 +125,11 @@ end
 Get the backtrace of the current exception, for use within `catch` blocks.
 """
 function catch_backtrace()
-    bt, bt2 = ccall(:jl_get_backtrace, Ref{SimpleVector}, ())
-    return _reformat_bt(bt::Vector{Ptr{Cvoid}}, bt2::Vector{Any})
+    bt1, bt2 = ccall(:jl_get_backtrace, Ref{SimpleVector}, ())
+    t = @_gc_preserve_begin bt2
+    bt = _reformat_bt(bt1::Vector{Ptr{Cvoid}})
+    @_gc_preserve_end t
+    return bt
 end
 
 """
@@ -146,7 +155,14 @@ function catch_stack(task=current_task(); include_bt=true)
     stride = include_bt ? 3 : 1
     for i = reverse(1:stride:length(raw))
         e = raw[i]
-        push!(formatted, include_bt ? (e,Base._reformat_bt(raw[i+1],raw[i+2])) : e)
+        if include_bt
+            bt1, bt2 = raw[i+1], raw[i+2]
+            t = @_gc_preserve_begin bt2
+            push!(formatted, (e, Base._reformat_bt(bt1)))
+            @_gc_preserve_end t
+        else
+            push!(formatted, e)
+        end
     end
     formatted
 end