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

[Andrew Burgess <aburgess@redhat.com>]

Muhammad Kamran <muhammad.kamran@arm.com> writes:

> GDB calls find_function_in_inferior ("malloc") when expression
> evaluation needs to allocate memory in the inferior, e.g. for string
> literal arguments.
>
> The minimal-symbol fallback created a synthetic ordinary function
> pointer from msymbol.value_address ().  If the symbol was a GNU IFUNC,
> this discarded the IFUNC marker, so call_function_by_hand did not
> resolve the symbol before calling it.
>
> Use find_minsym_type_and_address to classify the minimal symbol and
> propagate the GNU IFUNC marker to the synthetic function type.  This
> keeps the existing fallback return type while allowing inferior calls
> through IFUNC symbols to be resolved correctly.
> ---
>  gdb/valops.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Is it possible to create a test for this issue that would fail on other
targets?  There's gdb.base/gnu-ifunc.exp, from the patch I'm wondering
if all that would be needed is to place an ifunc function in a library,
and compile the library without debug information?  It's not super clear
from your description the exact steps that are needed to trigger this
bug.

>
> 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);

There are other places in GDB where we use lookup_function_type, could
these also run into this issue?  It would be nice if the description
explained why other similar places in GDB don't need changing if that's
the case.

Thanks,
Andrew


>  
>  	  if (objf_p)
>  	    *objf_p = objfile;
> -- 
> 2.43.0