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

[Florian Weimer <fweimer@redhat.com>]

* Muhammad Kamran:

> GDB calls find_function_in_inferior ("malloc") when expression
> evaluation needs to allocate memory in the inferior, e.g. for string
> literal arguments.

So this looks fairly nasty.  This looks fairly harmless as far as GDB
expressions go:

> +    gdb_test "print (get_string (\"hello-ifunc\"), str_in_arena ())" \

We can actually detect the GDB call and glibc and do the right thing:

  [PATCH 0/2] Work around GDB bug overwriting __libc_malloc
  <https://inbox.sourceware.org/libc-alpha/cover.1782766548.git.fweimer@redhat.com/>

Of course the GDB bug still needs fixing.

By the way, I don't think there is a safe way for GDB to call IFUNC
resolvers.  IFUNC resolvers in glibc may assume the presence of extra
data that was not there in the initial definition of the interface.
This shouldn't matter for malloc: elf_gnu_ifunc_resolve_by_got should
always be able obtain the pre-relocated address (except before
relocation has happened).

Does your patch change the behavior and output of this?

(gdb) print strcpy
$1 = {<text gnu-indirect-function variable, no debug info>} 0x7ffff7e0b8f0 <strcpy_ifunc>

Currently, the workaround looks like this:

(gdb) print dlsym(0, "strcpy")
$2 = (void *) 0x7ffff7ecb970 <__strcpy_avx2>

Maybe going through dlsym would also be the right way to do the inferior
calls involving IFUNC resolvers.  We can also provide a symbol that GDB
can call to make the IFUNC resolver call, given its handler address.

Thanks,
Florian