Setter for Dwfl's offline_next_address

  Added a new function dwfl_set_offline_next_addres which will 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.

Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
---
 libdwfl/libdwfl.h | 3 +++
 libdwfl/offline.c | 6 ++++++
 2 files changed, 9 insertions(+)
  

Hi Martin,

On Fri, Mar 01, 2024 at 05:04:05PM -0300, Martin Rodriguez Reboredo wrote:
> Added a new function dwfl_set_offline_next_addres which will 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 give an example or testcase for this?

Thanks,

Mark
  

Oh hi Mark!

On 3/2/24 17:47, Mark Wielaard wrote:
> Hi Martin,
> 
> On Fri, Mar 01, 2024 at 05:04:05PM -0300, Martin Rodriguez Reboredo wrote:
>> Added a new function dwfl_set_offline_next_addres which will 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 give an example or testcase for this?

This is intended for the Linux kernel perf tool so you might see it in
action when I publish the changes. In regards to testing I thought that
it was not needed due to the patch being a simple setter, but as
requested I can think something in the lines of.

     int
     main (int argc, char **argv)
     {
       Dwfl *dwfl = dwfl_begin (&offline_callbacks);
       assert (dwfl != NULL);

       if (dwfl->offline_next_address != OFFLINE_REDZONE)
         {
           dwfl_end (dwfl);
           return 1;
         }

       int result = 0;
       dwfl_set_offline_next_address (dwfl, 0);
       if (dwfl->offline_next_address != 0)
               result = 1;

       dwfl_end (dwfl);

       return result;
     }

But this will require libdwflP.h to be included, maybe if I add a getter
too it'd remedy it. Thoughts?

> 
> Thanks,
> 
> Mark
  

Hi Martin,

On Sat, Mar 02, 2024 at 07:43:38PM -0300, Martin Rodriguez Reboredo wrote:
> On 3/2/24 17:47, Mark Wielaard wrote:
> >On Fri, Mar 01, 2024 at 05:04:05PM -0300, Martin Rodriguez Reboredo wrote:
> >>Added a new function dwfl_set_offline_next_addres which will 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 give an example or testcase for this?
> 
> This is intended for the Linux kernel perf tool so you might see it in
> action when I publish the changes. In regards to testing I thought that
> it was not needed due to the patch being a simple setter, but as
> requested I can think something in the lines of.

It would be interesting to see the perf tool patch. I don't understand
the use case. So I assume perf currently does something which is wrong
and with your patch calling this new dwfl_set_offline_next_addres it
will do the right thing. That is what I was thinking of when asking
for an example or testcase. I agree that on itself such a simple
setter doesn't need a dedicated testcase. But maybe we can come up
with a testcase given the right context.

Cheers,

Mark
  

On 3/2/24 21:05, Mark Wielaard wrote:
> Hi Martin,
> 
> [...]
> 
> It would be interesting to see the perf tool patch. I don't understand
> the use case. So I assume perf currently does something which is wrong
> and with your patch calling this new dwfl_set_offline_next_addres it
> will do the right thing. That is what I was thinking of when asking
> for an example or testcase. I agree that on itself such a simple
> setter doesn't need a dedicated testcase. But maybe we can come up
> with a testcase given the right context.

Erm, I think I have a more clear example. When I use libdw to do
something like addr2line with an ELF file I fail to get the address
source line. Then I saw that eu-addr2line sets offline_next_address to
zero. The following is the program I've used to see the source info of
an address.

     int main(int argc, const char **argv)
     {
       if (argc != 3)
         return 1;

       Dwfl *dwfl = dwfl_begin(&offline_callbacks);
       if (!dwfl)
         return 1;
       dwfl_set_offline_next_address(dwfl, 0);

       if (!dwfl_report_offline(dwfl, "", argv[1], -1)) {
         dwfl_end(dwfl);
         return 1;
       }
       if (dwfl_report_end(dwfl, NULL, NULL)) {
         dwfl_end(dwfl);
         return 1;
       }

       char *endp = NULL;
       GElf_Addr addr = strtoumax(argv[2], &endp, 16);

       Dwfl_Module *mod = dwfl_addrmodule(dwfl, addr);

       int width = get_addr_width(mod);
       printf("0x%.*" PRIx64 "\n", width, addr);

       GElf_Sym s;
       GElf_Off off = 0;
       const char *name =
         dwfl_module_addrinfo(mod, addr, &off, &s, NULL, NULL, NULL);

       Dwfl_Line *line = dwfl_module_getsrc(mod, addr);
       if (!line)
         line = dwfl_getsrc(dwfl, addr);
       if (line) {
         int nline, column;
         const char *filename =
           dwfl_lineinfo(line, &addr, &nline, &column, NULL, NULL);
         printf("%s:%i,%i\n", filename, nline, column);
       } else {
         printf("??:0\n");
       }

       dwfl_end(dwfl);

       return 0;
     }

It could print the symbol name but that would've made the program
much longer but I think that this should be clear now.

> 
> Cheers,
> 
> Mark