Re: [PATCH] DWARF: add abstract origin links on lexical blocks DIEs

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Jan 15, 2016 at 3:41 PM, Pierre-Marie de Rodat
<derodat@adacore.comwrote:
> On 01/13/2016 01:17 PM, Richard Biener wrote:
>>
>> I wonder if you can construct a guality testcase that passes with and
>> fails without
>> the patch?
>
>
> I’ve tried to first look at how guality testcases are written (thanks for
> your answers on IRC, by the way :-)) and then how I could write a testcase
> for my fix. It seems there are two ways: match patterns in the assembly file
> or evaluate an expression in GDB.
>
> I already have the testcase I used during development: it’s written in Ada,
> to build with -O2. The way it checks the fix is to see if GDB manages to put
> a breakpoint on the Child2 symbol before executing the program (it cannot
> before my fix and it can afterwards). Oh, and it requires a fairly recent
> GDB version (7.10 looks good).
>
> I managed to get a similar GNU C99 reproducer (it’s attached): the debugging
> information has the pattern that exhibits the bugfix. Namely: while the
> “parent” function is inlined, the “child” function (which is in a block
> inside “parent”) is not. So GDB relies on the DW_TAG_abstract_origin in the
> inlined block to refer to the abstract block that contains the DIE that
> materializes “child“.
>
> However, it looks like there is no way in GDB to refer to C nested functions
> when they are not in the current scope:
>>
>> $ gcc -g -O2 -std=gnu99 nested_fun.c nested_fun_helpers.c
>> $ gdb -n -q ./a.out
>> (gdb) ptype child
>> No symbol "child" in current context.
>> (gdb) ptype nested_fun.parent.child
>> No symbol "nested_fun" in current context.
>
>
> On the other hand, this works with the Ada testcase:
>>
>> (gdb) ptype nested_fun.parent.child
>> type = (false, true)
>
>
> So I’m not sure what to do next: should I do a fragile testcase based on
> scanning the assembly file? (it could break with an optimizer change) create
> a guality testsuite for Ada?

Sounds like a good excuse to add a guality for Ada (which has unique
needs for dwarf).

Richard.

>> Anyway, the patch looks ok to me but please give others a chance to chime
>> in.
>
>
> Sure. Thank you for reviewing!
>
> --
> Pierre-Marie de Rodat