Re: [PATCH] decode_stacktrace: Support heuristic caller address search

[Sasha Levin]

On Fri, Mar 06, 2026 at 01:32:41AM +0900, Masami Hiramatsu wrote:
> On Thu, 5 Mar 2026 10:51:47 -0500
> Sasha Levin <sashal@xxxxxxxxxx> wrote:
> > DWARF line tables map address *ranges* to source lines, so any address
> > within the CALL instruction resolves to the correct source line.
> > return_addr-1 is guaranteed to land inside the CALL instruction (it's
> > the last byte of it), so a single addr2line call is sufficient.
>
> Ah, got it, OK. I also confirmed "addr-1" works. But if there is no lineinfo
> entry for the call instruction, shouldn't we check more instructions before
> the call?

There's no such thing as "no lineinfo entry for the call instruction" - DWARF
line tables are range-based, not discrete points. Each row covers all addresses
up to the next row, so every address within a function resolves to some source
line. addr-1 lands inside the CALL instruction and will always resolve to same
line as the CALL itself.

We show "??:0" because the address we passed falls outside of any DWARF
compilation unit altogether.

--
Thanks,
Sasha