Re: Breaking on C labels?

Jim Blandy
2007-01-25T21:19:19Z

Joel Brobecker <brobecker@adacore.com> writes:
> A customer asked us a question about the ability of breaking on labels
> inside C code. Consider for instance:
>
> void
> procedure foo (void)
> {
> [...]
> error_handler:
> [...]
> }
>
> The customer asked if it was possible to break at the error_handler
> label. We are helping them with finding alternative solutions, but
> I still did a bit of researching...
>
> I discovered without much surprise that DWARF does indeed have provision
> for labels (DW_TAG_label). However, I also noticed that GCC already
> generates the associated DIEs. We actually even process them. However,
> all my attempts in trying to reference them from the debugger failed.
> I tried "break error_handler", or more simply "p error_handler", etc.
>
> Did we ever make any attempt in implementing this sort of functionality
> in the past?
>
> Looking at the source code, I found in new_symbol ():
>
> case DW_TAG_label:
> attr = dwarf2_attr (die, DW_AT_low_pc, cu);
> if (attr)
> {
> SYMBOL_VALUE_ADDRESS (sym) = DW_ADDR (attr) + baseaddr;
> }
> SYMBOL_CLASS (sym) = LOC_LABEL;
> break;
>
> So we setup the symbol, but we don't add to any of our symbol lists...
> I am left wondering what it is that we'll be doing with this symbol.

You're right, it looks to me as if we just throw the symbol away, too.

The logical thing would be to put it in the block of the function it's
in, since goto labels are block-scoped. It would go in LABEL_DOMAIN,
since that's a separate namespace. And then you'd need to teach
linespec.[ch] about them.