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SubjectRe: [PATCH] perf srcline: Implement addr2line using libdw
Hello,

On Thu, Apr 4, 2024 at 5:10 PM Martin Rodriguez Reboredo
<yakoyoku@gmail.com> wrote:
>
> On 4/1/24 8:31 PM, Namhyung Kim wrote:
> > [...]
> >
> > Thanks for doing this! Yep, we could unset the env temporarily.
> >
> > As a general comment, perf has some helper functions for libdw
> > in util/dwarf-aux.[ch]. Please take a look and use/update them.
>
> Whoops! I haven't seen that file, thanks for mentioning it.
>
> > [...]
> >
> > Probably we can use cu_find_lineinfo().
>
> I could use that, I'll see.
>
> > [...]
> >
> >>> +static struct a2l_data *addr2line_init(const char *path)
> >
> > debuginfo__new()?
>
> `libdw_a2l_new` can be another option too.
>
> > [...]
> >
> >>> +static int get_inline_function(struct dso *dso, struct inline_node *node,
> >>> + struct symbol *sym)
> >>> +{
> >>> + struct a2l_data *a2l = dso->a2l;
> >>> + Dwarf_Addr addr = a2l->addr + a2l->bias;
> >>> + Dwarf_Addr bias = 0;
> >>> + Dwarf_Die *cudie = dwfl_module_addrdie(a2l->mod, addr, &bias);
> >>> +
> >>> + Dwarf_Die *scopes = NULL;
> >>> + int nscopes = dwarf_getscopes(cudie, addr - bias, &scopes);
> >
> > It's not clear to me how this dwarf_getscopes() and later
> > dwarf_getscopes_die() work together. Can you please add some
> > comment? Also we have die_get_scopes() and I think it's simpler.
>
> I think the first is to get the scopes at an address and the second is
> for the scopes with the addr offset at that DIE. Off the top of my head.
>
> > [...]
> >
> > Why not get the function name from the abstract origin?
>
> I'm not getting it, where's that abstract origin?

IIUC DW_TAG_inlined_subroutine has DW_AT_abstract_origin
to point to the original definition of the function. It should have
the name of the function.

<2><5ca8>: Abbrev Number: 40 (DW_TAG_inlined_subroutine)
<5ca9> DW_AT_abstract_origin: <0x5eeb>
<5cad> DW_AT_low_pc : 0x24efc6
<5cb5> DW_AT_high_pc : 0x2d
<5cbd> DW_AT_call_file : 3
<5cbe> DW_AT_call_line : 135
<5cbf> DW_AT_call_column : 9

Thanks,
Namhyung

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