[llvm] r187656 - Bugfix for making the DWARF debug strings and labels to code emitted as secrel32 instead of long opcodes (only for coff). This makes them debuggable with GDB (with fix for 64bits msvc)

[Carlo Kok]

Op 2-8-2013 23:30, David Blaikie schreef:
>
> Do you know if this is a limitation of the format, or just of the
> debugger's ability to read? I've hit bugs before where only the 32 or
> 64 bit case have been implemented because that's all that was needed.
> If there is a sensible generic solution to 32 and 64 bit and it's just
> GDB (or the linker) being silly & special casing, then it'd be nice to
> document that we're working around a bug in another tool (& file a bug
> for that tool).
>
> If you can use a .quad address, I'd expect a .long address if it
> needed to be 32 bits.
>


You are right. GDB just didn't show the failure after this. as Vadim 
noted in the last comment here
http://llvm.org/bugs/show_bug.cgi?id=16249

It did load it, but didn't set a proper breakpoint when using "start" (I 
used run). I spent some more time researching this, what really needed 
to happen was that for dwarf addresses it shouldn't use secrel, for all 
others it should. Attached is a new patch that does this (had to 
introduce a new parameter as the dwarf type wasn't available at that level).

There were a few forms used for addresses that I could find:
dwarf::DW_FORM_addr
dwarf::DW_FORM_udata
dwarf::DW_FORM_sdata

these all pointed to text/data segments (in which it shouldn't use 
secrel). Attached is an incremental patch tested on 32 and 64bits mingw, 
if this patch is oke I'll commit, gdb now properly steps when using 
start too (on both mingw 32 and 64):

clang -target x86_64-pc-mingw32 -g test2.c -o test2.exe
gdb test2.exe
...
This GDB was configured as "x86_64-w64-mingw32".
(gdb) start
Temporary breakpoint 1 at 0x401529: file test2.c, line 8.
Starting program: C:\Projects\nco\cfe64\bin\Debug\test2.exe
[New Thread 38532.0xa3c4]

Temporary breakpoint 1, main () at test2.c:8
8               foobar(17);
(gdb) step
foobar (x=17) at test2.c:3
3           return x+42;
(gdb) step
main () at test2.c:9
9               return 0;
(gdb) step


--
Carlo Kok
-------------- next part --------------
Index: include/llvm/CodeGen/AsmPrinter.h
===================================================================
--- include/llvm/CodeGen/AsmPrinter.h	(revision 187993)
+++ include/llvm/CodeGen/AsmPrinter.h	(working copy)
@@ -359,13 +359,13 @@
     /// where the size in bytes of the directive is specified by Size and Label
     /// specifies the label.  This implicitly uses .set if it is available.
     void EmitLabelPlusOffset(const MCSymbol *Label, uint64_t Offset,
-                                   unsigned Size) const;
+                                   unsigned Size, bool IsAddress = false) const;
 
     /// EmitLabelReference - Emit something like ".long Label"
     /// where the size in bytes of the directive is specified by Size and Label
     /// specifies the label.
-    void EmitLabelReference(const MCSymbol *Label, unsigned Size) const {
-      EmitLabelPlusOffset(Label, 0, Size);
+    void EmitLabelReference(const MCSymbol *Label, unsigned Size, bool IsAddress = false) const {
+      EmitLabelPlusOffset(Label, 0, Size, IsAddress);
     }
 
     //===------------------------------------------------------------------===//
Index: lib/CodeGen/AsmPrinter/AsmPrinter.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/AsmPrinter.cpp	(revision 187993)
+++ lib/CodeGen/AsmPrinter/AsmPrinter.cpp	(working copy)
@@ -1415,9 +1415,9 @@
 /// where the size in bytes of the directive is specified by Size and Label
 /// specifies the label.  This implicitly uses .set if it is available.
 void AsmPrinter::EmitLabelPlusOffset(const MCSymbol *Label, uint64_t Offset,
-                                      unsigned Size)
+                                      unsigned Size, bool IsAddress)
   const {
-  if (MAI->needsDwarfSectionOffsetDirective() && Size == 4) { // secrel32 ONLY works for 32bits.
+  if (MAI->needsDwarfSectionOffsetDirective() && !IsAddress) { // secrel32 ONLY works for 32bits.
     OutStreamer.EmitCOFFSecRel32(Label);
     return;
   }
Index: lib/CodeGen/AsmPrinter/DIE.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DIE.cpp	(revision 187993)
+++ lib/CodeGen/AsmPrinter/DIE.cpp	(working copy)
@@ -293,7 +293,8 @@
 /// EmitValue - Emit label value.
 ///
 void DIELabel::EmitValue(AsmPrinter *AP, uint16_t Form) const {
-  AP->EmitLabelReference(Label, SizeOf(AP, Form));
+  AP->EmitLabelReference(Label, SizeOf(AP, Form), Form == dwarf::DW_FORM_addr 
+    || Form == dwarf::DW_FORM_udata || Form == dwarf::DW_FORM_sdata);
 }
 
 /// SizeOf - Determine size of label value in bytes.