RE: [PATCH 09/12] gdb, gdbarch: Enable inferior calls for shadow stack support.

["Schimpe, Christina" <christina.schimpe@intel.com>]

> -----Original Message-----
> From: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> Sent: Thursday, February 6, 2025 4:32 AM
> To: Schimpe, Christina <christina.schimpe@intel.com>
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 09/12] gdb, gdbarch: Enable inferior calls for shadow stack
> support.
> 
> 
> "Schimpe, Christina" <christina.schimpe@intel.com> writes:
> 
> > diff --git a/gdb/infcall.c b/gdb/infcall.c index
> > 6399278c6ae..3a4f1e35a2f 100644
> > --- a/gdb/infcall.c
> > +++ b/gdb/infcall.c
> > @@ -1453,6 +1453,12 @@ call_function_by_hand_dummy (struct value
> *function,
> >  				bp_addr, args.size (), args.data (),
> >  				sp, return_method, struct_addr);
> >
> > +  /* Push the return address of the inferior (bp_addr) on the shadow stack
> > +     and update the shadow stack pointer.  As we don't execute a call
> > +     instruction to start the inferior we need to handle this
> > + manually.  */  if (gdbarch_shadow_stack_push_p (gdbarch))
> > +    gdbarch_shadow_stack_push (gdbarch, bp_addr);
> > +
> 
> For AArch64's Guarded Control Stack, instead of adding a new gdbarch method I
> added this change to aarch64_push_dummy_call:
> 
>   if (aarch64_gcs_is_enabled (regcache))
>     aarch64_push_gcs_entry (regcache, bp_addr);
> 
> To implement aarch64_gcs_is_enabled I did add a new method to
> aarch64_gdbarch_tdep so that OS-independent code in aarch64-tdep.c could call
> Linux-specific logic in aarch64-linux-tdep.c:
> 
> static bool
> aarch64_gcs_is_enabled (regcache *regs)
> {
>   gdbarch *arch = regs->arch ();
>   aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (arch);
> 
>   if (tdep->gcs_is_enabled == nullptr)
>     return false;
> 
>   return tdep->gcs_is_enabled (regs);
> }
> 
> Wouldn't a similar approach work for amd64?

Hi Thiago, 

Thank you for the feedback!

I think I could also fix it in amd64_push_dummy_call by implementing it in a similar way than you do. 
But isn't it better to keep the code generic ?

Generic code for handling shadow stacks is also required for the implementation of "bt shadow",
as I tried to provide an implementation that can be used by other architectures as well.

Christina


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