Re: [PATCH v2 1/1] gdb: Preserve IFUNC marker when finding inferior functions

[Simon Marchi <simark@simark.ca>]

On 2026-06-26 05:24, Muhammad Kamran wrote:
> Hi Simon,
> 
> On 25/06/2026 21:05, Simon Marchi wrote:
>>
>>> @@ -356,6 +361,39 @@ proc misc_tests {resolver_attr resolver_debug final_debug} {
>>>       }
>>>   }
>>>   +# Test that GDB resolves a GNU IFUNC minimal symbol when it uses
>>> +# find_function_in_inferior to make an internal inferior call.  String
>>> +# literals are copied into the inferior with a call to malloc, so a
>>> +# no-debug IFUNC malloc exercises the minimal-symbol fallback.
>>> +
>>> +proc_with_prefix test_inferior_call {} {
>>> +    global srcdir subdir
>>> +    global infcall_file infcall_src
>>> +    global infcall_malloc_file infcall_malloc_src
>>> +
>>> +    set executable $infcall_file
>>> +    set binfile [standard_output_file $executable]
>>> +    set malloc_obj [standard_output_file ${infcall_malloc_file}.o]
>>> +
>>> +    if { [gdb_compile ${srcdir}/${subdir}/${infcall_malloc_src} \
>>> +          $malloc_obj object {}] != ""
>>> +     || [gdb_compile [list ${srcdir}/${subdir}/${infcall_src} \
>>> +                  $malloc_obj] \
>>> +         $binfile executable {debug}] != "" } {
>>> +    untested "failed to compile inferior call testcase"
>>> +    return
>>> +    }
>>
>> I think that the test should also cover the case where we do have debug
>> info.  However, the gdb.base/gnu-ifunc.exp test is already written in
>> a such a way that it tests all imaginable combinations:
>>
>> # Test all the combinations of:
>> #
>> # - An ifunc resolver with the same name as the ifunc symbol vs an
>> #   ifunc resolver with a different name as the ifunc symbol.
>> #
>> # - ifunc resolver compiled with and without debug info.  This ensures
>> #   that GDB understands that a function not a regular function by
>> #   looking at the STT_GNU_IFUNC type in the elf symbols.  DWARF has
>> #   no way to express the STT_GNU_IFUNC type.
>> #
>> # - ifunc target function (resolved) compiled with and without debug
>> #   info.
>> foreach_with_prefix resolver_attr {0 1} {
>>      foreach_with_prefix resolver_debug {0 1} {
>>     foreach_with_prefix final_debug {0 1} {
>>         if { [build $resolver_attr $resolver_debug $final_debug] != 0 } {
>>         misc_tests $resolver_attr $resolver_debug $final_debug
>>         set-break $resolver_attr $resolver_debug $final_debug
>>         }
>>     }
>>      }
>> }
>>
>> Could you somehow hook the new infcall tests into that, so that we also
>> test infcalls in all imaginable situations.
>>
> 
> I've extended the test to run through the existing
> resolver_attr/resolver_debug/final_debug matrix.  With only the test
> change, the new inferior-call test fails in all eight combinations on
> AArch64, so the issue is wider than the original no-debug minimal-symbol
> case.  I'll work on the patch accordingly and post a new version once I
> have the patch ready.
> 
>>> diff --git a/gdb/valops.c b/gdb/valops.c
>>> index ab6fd5079e1..7d305871efc 100644
>>> --- a/gdb/valops.c
>>> +++ b/gdb/valops.c
>>> @@ -133,11 +133,15 @@ find_function_in_inferior (const char *name, struct objfile **objf_p)
>>>         struct gdbarch *gdbarch = objfile->arch ();
>>>           struct type *type;
>>> +      struct type *resolved_type;
>>>         CORE_ADDR maddr;
>>>         type = lookup_pointer_type (builtin_type (gdbarch)->builtin_char);
>>>         type = lookup_function_type (type);
>>>         type = lookup_pointer_type (type);
>>> -      maddr = msymbol.value_address ();
>>> +      resolved_type = find_minsym_type_and_address (msymbol.minsym, objfile,
>>> +                            &maddr);
>>> +      if (resolved_type->is_gnu_ifunc ())
>>> +        type->target_type ()->set_is_gnu_ifunc (true);
>>
>> Calling find_minsym_type_and_address just to know if the minsym is an
>> ifunc seems rather heavyweight for nothing.  Can't we just check that
>> the minsym type is mst_text_gnu_ifunc?
>>
> 
> I used find_minsym_type_and_address because it keeps
> find_function_in_inferior consistent with normal minimal-symbol
> evaluation.  It also handles function-descriptor symbols:
> mst_data_gnu_ifunc may have a descriptor address as its value, and
> find_minsym_type_and_address can convert that to the code address and
> reclassify it as mst_text_gnu_ifunc.  A direct mst_text_gnu_ifunc check
> would miss that case, and value_address () could be the descriptor
> address rather than the callable address.
> For reference: gdb/minsyms.c:1594 has:
>   /* The minimal symbol might point to a function descriptor;
>      resolve it to the actual code address instead.  */
> 
> If you still prefer avoiding find_minsym_type_and_address here, I think
> we would need a helper that shares the same descriptor/address handling,
> rather than checking only mst_text_gnu_ifunc.

If the descriptor to actual address translation is really needed, then
find_minsym_type_and_address sounds fine.

Simon