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

[Muhammad Kamran <muhammad.kamran@arm.com>]

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.

Please share your thoughts.

Thanks,
Kamran

> I assume that the `maddr` output by find_minsym_type_and_address would
> always be equal to `msymbol.value_address ()`.
> 
> Side-note: this "find_function_in_inferior" (at least the fallback)
> really assumes that we are looking for a function returning "char *", so
> that function seems misnamed (it could easily be mis-used).
> 
> Simon