[PATCH 2/2] aarch64: Add workaround for GDB bug handling string literals

[Yury Khrustalev]

* Florian

On Mon, Jun 29, 2026 at 11:07:13PM +0200, Florian Weimer wrote:
> When GDB evaluates an expression in the inferior, it first
> creates a copy of the string using malloc.  For this malloc
> call, GDB was not tracking properly if the malloc symbol is
> actually an IFUNC resolver.  This means that the IFUNC
> resolver gets called like the real malloc function.
> 
> This change adds a kludge to detect this, which prevents GDB
> from overwriting the __libc_malloc code with the user-supplied
> string literal.
> 
> ...
> 
> diff --git a/sysdeps/aarch64/multiarch/malloc-ifuncs.c b/sysdeps/aarch64/multiarch/malloc-ifuncs.c
> index 648fb617de..3552168ecd 100644
>
> ...
>
> +/* Return true if the resolver function has been called through GDB.
> +   This used below to determine if GDB incorrectly calls the malloc
> +   IFUNC resolver instead of the resolver result.  The trampoline
> +   address is either on the stack, or the kernel-provided entry point,
> +   depending on architecture.
> +
> +   A fixed GDB will get the malloc address from the GOT.  Calling
> +   malloc before relocation processing is complete should use the
> +   ld.so malloc, which does not involve an IFUNC.  */
> +static inline bool
> +called_from_gdb (uintptr_t return_address, uintptr_t stack_frame)
> +{
> +#ifdef SHARED
> +  /* Assume that the stack grows downwards.  */
> +  if (stack_frame <= return_address && return_address <= stack_frame + 128)
> +    return true;
> +
> +  /* GDB uses the kernel-provided entry point on some architectures
> +     for the trampoline.  */
> +  if (return_address == GLRO(dl_entry))
> +    return true;
> +#endif
> +  return false;
> +}

Although this does fix the regressions in GDB testsuite, I think this is
a wrong approach and we should not do this.

Thanks,
Yury