Re: gdb 8.x - g++ 7.x compatibility

Michael Matz
2018-02-07T16:26:35Z

Hi,

On Wed, 7 Feb 2018, Simon Marchi wrote:

> This addresses the issue of how to do good software design in GDB to
> support different producers cleanly, but I think we have some issues
> even before that, like how to support g++ 7.3 and up. I'll try to
> summarize the issue quickly. It's now possible to end up with two
> templated classes with the same name that differ only by the signedness
> of their non-type template parameter. One is Foo<int N> and the other
> is Foo<unsigned int N> (the 10 is unsigned). Until 7.3, g++ would
> generate names like Foo<10> for the former and names like Foo<10u> for
> the later (in the DW_AT_name attribute of the classes' DIEs). Since 7.3,
> it produces Foo<10> for both.

Yeah, gdb needs a way to lookup types by name, and since the change
DW_AT_name can't be used for this anymore. Either that needs to be
fixed/reverted, or we do the more obvious thing: since types in C++ have
linkage it makes sense to add the linkage (i.e. mangled) name to the types
DIE using the traditional DW_AT_MIPS_linkage_name.

That latter solution would have the advantage that you don't need to
demangle anything anymore. From vtable you get to typeinfo, from there
for typeinfo name, and that contains the mangled type name (without _Z
prefix).

Ciao,
Michael.