Re: PATCH to dwarf2read.c:decode_locdesc

Elena Zannoni
2002-01-10T22:07:11Z

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;
>