Re: [RFA] Nullified garbage-collected global variables

[Jerome Guitton <guitton at adacore dot com>]

Tom Tromey (tromey@redhat.com):

> >>>>> "Jerome" == Jerome Guitton <guitton@adacore.com> writes:
> 
> Jerome> 	* dwarf2read.c (add_partial_symbol): Do not add a global variable if
> Jerome> 	its adress is null. Add comment to explain why.
> 
> I am not totally sure about this.  The patch itself looks reasonable,
> but I have a couple of questions.
> 
> Do you need to apply the same treatment to full symbols?  What happens
> if the psymtab is expanded for some other reason and a full symbol of
> this sort is then created?  Or is that already impossible?
> 
> What about has_section_at_zero?

Here is a new patch that should fix these issues. I have tested it on
x86-linux, no regression.

OK to apply?

gdb/ChangeLog:

	* dwarf2read.c (add_partial_symbol): Do not add a global variable if
	its adress is null. Add comment to explain why.
	(new_symbol): Ditto.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 288d777..15926c6 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -3427,7 +3427,10 @@ add_partial_symbol (struct partial_die_info *pdi, struct dwarf2_cu *cu)
 	     Don't enter into the minimal symbol tables as there is
 	     a minimal symbol table entry from the ELF symbols already.
 	     Enter into partial symbol table if it has a location
-	     descriptor or a type.
+	     descriptor or a type.  A global variable may also have been
+	     stripped out by the linker if unused, in which case its
+	     address will be nullified; do not add such variables into
+	     partial symbol table then.
 	     If the location descriptor is missing, new_symbol will create
 	     a LOC_UNRESOLVED symbol, the address of the variable will then
 	     be determined from the minimal symbol table whenever the variable
@@ -3438,7 +3441,9 @@ add_partial_symbol (struct partial_die_info *pdi, struct dwarf2_cu *cu)
 
 	  if (pdi->locdesc)
 	    addr = decode_locdesc (pdi->locdesc, cu);
-	  if (pdi->locdesc || pdi->has_type)
+	  if ((pdi->locdesc
+	       && (addr || dwarf2_per_objfile->has_section_at_zero))
+	      || (!pdi->locdesc && pdi->has_type))
 	    psym = add_psymbol_to_list (actual_name, strlen (actual_name),
 					built_actual_name,
 					VAR_DOMAIN, LOC_STATIC,
@@ -9860,7 +9865,16 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu)
 	    {
 	      var_decode_location (attr, sym, cu);
 	      attr2 = dwarf2_attr (die, DW_AT_external, cu);
-	      if (attr2 && (DW_UNSND (attr2) != 0))
+	      if (SYMBOL_CLASS (sym) == LOC_STATIC
+		  && SYMBOL_VALUE_ADDRESS (sym) == 0
+		  && !dwarf2_per_objfile->has_section_at_zero)
+		{
+		  /* When a static variable is eliminated by the linker,
+		     the corresponding debug information is not stripped
+		     out, but the variable address is set to null;
+		     do not add such variables into symbol table.  */
+		}
+	      else if (attr2 && (DW_UNSND (attr2) != 0))
 		{
 		  struct pending **list_to_add;