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Re: Patch for pascal-dynamic arrays


On Sun, 2010-05-16 at 14:04 +0200, Jonas Maebe wrote:
> On 15 May 2010, at 23:44, Jan Kratochvil wrote:
> 
> > But if the "allocation" is just an internal
> > compiler issue which should be hidden by the same compiler at the DWARF level.
> > Therefore I would guess to use some:
> > 	drop DW_TAG_array_type -> DW_AT_allocated
> > 	DW_TAG_subrange_type -> DW_AT_upper_bound:
> > 		DW_OP_push_object_address
> > 		DW_OP_deref
> > 		DW_OP_dup
> > 		DW_OP_bra allocated
> > 			DW_OP_lit0
> > 			DW_OP_skip end
> > 		allocated:
> > 			DW_OP_lit8
> > 			DW_OP_minus
> > 			DW_OP_deref
> > 		end:
> 
> I agree. Joost, I've attached a patch for FPC's DWARF writer to fix it. I can't test whether it works (the dumped DWARF info looks ok though), because I can't get gdb/F-13 to build:

It doesn't work.

That's because type_length_get() (gdbtypes.c) does not return 0 when the
high and low-bound are equal to each other. Instead it returns the
element-size. Then allocate_value_lazy tries to read element-size bytes
from the base-address (being 0x0) -> av.

I think that type_length_get() not returning 0 is a bug, (also because
there is a comment in the function that some part of the code doesn't
handle count=0 right. But I think that should be count=1) but it could
be that it's on purpose for Fortran. Jan, can you comment on this?

There's also a second problem. The lower bound is 1 for strings. With
Jonas' patch for fpc the upper bound of strings is 0 when not allocated.
Leading to a size of -1. An easy fix, new patch is attached.

Joost.

Index: dbgdwarf.pas
===================================================================
--- dbgdwarf.pas	(revision 15284)
+++ dbgdwarf.pas	(working copy)
@@ -3558,9 +3558,6 @@
             ]);
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_push_object_address)));
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
-        append_block1(DW_AT_allocated,2);
-        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_push_object_address)));
-        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
 
         append_labelentry_ref(DW_AT_type,def_dwarf_lab(def.elementdef));
         finish_entry;
@@ -3568,10 +3565,19 @@
         append_entry(DW_TAG_subrange_type,false,[
           DW_AT_byte_stride,DW_FORM_udata,def.elesize,
           DW_AT_lower_bound,DW_FORM_udata,0,
-          DW_AT_upper_bound,DW_FORM_block1,5
+          DW_AT_upper_bound,DW_FORM_block1,13
           ]);
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_push_object_address)));
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_dup)));
+        { pointer = nil? }
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_bra)));
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_16bit(4));
+        { yes -> length = 0 }
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_lit0)));
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_skip)));
+        current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_16bit(3));
+        { no -> load length }
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_lit0)+sizeof(ptrint)));
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_minus)));
         current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
@@ -3607,13 +3613,6 @@
                 we point to address of the string
               }
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
-
-              { also add how to detect whether or not the string is allocated: if the pointer is 0
-                then it isn't, otherwise it is
-              }
-              append_block1(DW_AT_allocated,2);
-              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_push_object_address)));
-              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
             end
           else
             begin
@@ -3630,9 +3629,9 @@
           if deref then
             begin
               if (chardef.size=1) then
-                upperopcodes:=5
+                upperopcodes:=13
               else
-                upperopcodes:=7;
+                upperopcodes:=15;
               { lower bound is always 1, upper bound (length) needs to be calculated }
               append_entry(DW_TAG_subrange_type,false,[
                 DW_AT_lower_bound,DW_FORM_udata,1,
@@ -3642,14 +3641,24 @@
               { high(string) is stored sizeof(ptrint) bytes before the string data }
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_push_object_address)));
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_dup)));
+              { pointer = nil? }
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_bra)));
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_16bit(4));
+              { yes -> length = 0 }
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_lit1)));
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_skip)));
+              current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_16bit(3));
+              { no -> load length }
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_lit0)+sizeof(ptrint)));
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_minus)));
               current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_deref)));
+
               { for widestrings, the length is specified in bytes, so divide by two }
-              if (upperopcodes=7) then
+              if (upperopcodes=15) then
                 begin
                   current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_lit1)));
-                  current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_shra)));
+                  current_asmdata.asmlists[al_dwarf_info].concat(tai_const.create_8bit(ord(DW_OP_shr)));
                 end;
             end
           else

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