Re: PATCH to dwarf2read.c:decode_locdesc

[Elena Zannoni <ezannoni at redhat dot com>]

Jason Merrill writes:
 > I noticed that even with Daniel's recent C++ improvements (thanks!), vbase
 > handling was still broken with dwarf2 because dwarf2read.c still didn't
 > grok the complex location expression gcc now emits.  As it happens, by a
 > fluke simply adding support for the missing opcodes causes decode_locdesc
 > to produce the answer gdb wants.  The dwarf2 output expects the stack to
 > start with the address of the object and produce the address of the base,
 > whereas in the current gdb the stack starts with 0 and produces the
 > negation of whatever constant is provided, which matches the stabs output.
 > 
 > Of course, gdb tries to complain about the derefs twice in the process, but
 > is currently muffled.
 > 
 > So, it's not a complete solution, but it's entirely correct and fixes
 > gdb.c++/inherit.exp.
 > 

Sigh! There have been several attempts to get the location expression
support in gdb. They all stopped dead for one reason or another. There
are several WIP patches out there.
http://sources.redhat.com/ml/gdb-patches/2001-02/msg00276.html
http://sources.redhat.com/ml/gdb-patches/2001-06/msg00390.html
http://sources.redhat.com/ml/gdb-patches/2001-06/msg00502.html
http://sources.redhat.com/ml/gdb-patches/2001-07/msg00008.html

Hmm, DW_OP_dup wasn't handled in the above patches.

Anyway, this is approved.

Elena


 > OK to commit?
 > 
 > 2002-01-10  Jason Merrill  <jason@redhat.com>
 > 
 > 	* dwarf2read.c (decode_locdesc): Implement DW_OP_litn, DW_OP_dup.
 > 	Fix DW_OP_minus.
 > 
 > *** dwarf2read.c.~1~	Tue Jan  8 14:17:30 2002
 > --- dwarf2read.c	Thu Jan 10 11:54:45 2002
 > *************** decode_locdesc (struct dwarf_block *blk,
 > *** 5807,5812 ****
 > --- 5807,5847 ----
 >         op = data[i++];
 >         switch (op)
 >   	{
 > + 	case DW_OP_lit0:
 > + 	case DW_OP_lit1:
 > + 	case DW_OP_lit2:
 > + 	case DW_OP_lit3:
 > + 	case DW_OP_lit4:
 > + 	case DW_OP_lit5:
 > + 	case DW_OP_lit6:
 > + 	case DW_OP_lit7:
 > + 	case DW_OP_lit8:
 > + 	case DW_OP_lit9:
 > + 	case DW_OP_lit10:
 > + 	case DW_OP_lit11:
 > + 	case DW_OP_lit12:
 > + 	case DW_OP_lit13:
 > + 	case DW_OP_lit14:
 > + 	case DW_OP_lit15:
 > + 	case DW_OP_lit16:
 > + 	case DW_OP_lit17:
 > + 	case DW_OP_lit18:
 > + 	case DW_OP_lit19:
 > + 	case DW_OP_lit20:
 > + 	case DW_OP_lit21:
 > + 	case DW_OP_lit22:
 > + 	case DW_OP_lit23:
 > + 	case DW_OP_lit24:
 > + 	case DW_OP_lit25:
 > + 	case DW_OP_lit26:
 > + 	case DW_OP_lit27:
 > + 	case DW_OP_lit28:
 > + 	case DW_OP_lit29:
 > + 	case DW_OP_lit30:
 > + 	case DW_OP_lit31:
 > + 	  stack[++stacki] = op - DW_OP_lit0;
 > + 	  break;
 > + 
 >   	case DW_OP_reg0:
 >   	case DW_OP_reg1:
 >   	case DW_OP_reg2:
 > *************** decode_locdesc (struct dwarf_block *blk,
 > *** 5965,5970 ****
 > --- 6000,6010 ----
 >   	  i += bytes_read;
 >   	  break;
 >   
 > + 	case DW_OP_dup:
 > + 	  stack[stacki + 1] = stack[stacki];
 > + 	  stacki++;
 > + 	  break;
 > + 
 >   	case DW_OP_plus:
 >   	  stack[stacki - 1] += stack[stacki];
 >   	  stacki--;
 > *************** decode_locdesc (struct dwarf_block *blk,
 > *** 5976,5982 ****
 >   	  break;
 >   
 >   	case DW_OP_minus:
 > ! 	  stack[stacki - 1] = stack[stacki] - stack[stacki - 1];
 >   	  stacki--;
 >   	  break;
 >   
 > --- 6016,6022 ----
 >   	  break;
 >   
 >   	case DW_OP_minus:
 > ! 	  stack[stacki - 1] -= stack[stacki];
 >   	  stacki--;
 >   	  break;
 >