[PATCH] Getter and setter for Dwfl's offline_next_address

[Martin Rodriguez Reboredo]

On 3/20/24 19:52, Mark Wielaard wrote:
> Hi Martin,
> 
> On Wed, Mar 06, 2024 at 04:22:49PM -0300, Martin Rodriguez Reboredo wrote:
>> Added new functions dwfl_get_offline_next_address and
>> dwfl_set_offline_next_address which will get plus set said field from
>> the Dwfl struct. This is a requirement for listing functions from their
>> addresses when using libdwfl offline, otherwise wrong symbols are going
>> to be returned.
> 
> Could you show an example of when/where you need it and what address
> you set it to?

For example, this test program reports the name and location pointed by
the passed address.

$ ./report /home/yakoyoku/.debug/.build-id/.../elf 0x0003281f
0x000000000003281f
??
??:0

But due to the mentioned bias both of them are unknown or out of range.

> The offline_next_address is only relevant for ET_REL files (like
> object files or kernel modules). In general you will need to check the
> bias, which various dwfl functions return to know the difference
> between the addresses in the ELF, Dwarf or the module load address.
> 
> That said, readelf, nm and dwfl_argp do "cheat" by setting the
> offline_next_address to zero if they know they are just inspecting a
> single object file. So maybe this is a functionality we need to
> expose. But I don't fully understand why you need both a getter and a
> setter for any arbitrary address.

I've erroneously thought that setting `offline_next_address` was a
requirement to obtain what I've needed. But if I use
`dwfl_module_getelf` or `dwfl_module_getdwarf` I can get the correct
name and location.

0x000000000003281f
_ZNSt11__copy_moveILb0ELb0ESt26random_access_iterator_tagE8__copy_mIPcPhEET0_T_S6_S5_
/usr/include/c++/13.2.1/bits/stl_algobase.h:388,18

So this patch is kinda pointless, but at least I've managed to learn
what I was missing. Anyways, thanks for the heads-up. :)