RE: [PATCH v2 1/3] gdb: Make tagged pointer support configurable.

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

Hi Luis,

> >>> -/* AArch64 implementation of the remove_non_address_bits gdbarch
> >> hook.
> >>> Remove
> >>> -   non address bits from a pointer value.  */
> >>> -
> >>> -static CORE_ADDR
> >>> +CORE_ADDR
> >>>  aarch64_remove_non_address_bits (struct gdbarch *gdbarch,
> CORE_ADDR
> >>> pointer)
> >>
> >> Shouldn't there still be some sort of comment for this function in the c
> file?
> >> At least some "see header file"? Though it seems like no function in
> >> aarch64- tdep.h has any comment, and all comments are in
> >> aarch64-tdep.c. I would also be fine with that for consistency. Maybe
> >> Luis can comment how he prefers it.
> >>
> >> But I am fine with this patch. Let's see if someone else objects this split.
> >>
> >> Reviewed-By: Felix Willgerodt <felix.willgerodt@intel.com>
> >>
> >> Thanks,
> >> Felix
> >
> > Ok, let's wait for further comments here.
> 
> Sorry, only spotted this now.
> 
> The comment on the above function would be a repetition of the hook
> explanation, and the gdbarch hook explanation covers all the details we
> need. But if the comment is being removed due to it being in the header, we
> should point to the header instead.
> 
> "See aarch64-tdep.h" should do.

Ok, I will add that line.

> There is something odd about this patch though. The aarch64 code is being
> changed to call aarch64_remove_non_address_bits directly, but 3 new hooks
> are being set:
> 
> +  set_gdbarch_remove_non_address_bits_watchpoint
> +    (gdbarch, aarch64_remove_non_address_bits);
> + set_gdbarch_remove_non_address_bits_breakpoint
> +    (gdbarch, aarch64_remove_non_address_bits);
> + set_gdbarch_remove_non_address_bits_memory
> +    (gdbarch, aarch64_remove_non_address_bits);
> 
> But the above hooks (the gdbarch_remove_non_address_bits_memory at
> least) never get used in aarch64 code. Is there a reason for that?

I thought it's wrong to call the gdbarch_remove_non_address_bits_memory hook in aarch64 code.
The reason is described here: https://sourceware.org/pipermail/gdb-patches/2024-May/209420.html

"Also I noticed that the gdbarch function 'gdbarch_remove_non_addr_bits_memory'
should not be used in several functions of aarch64* files (patch 1) due
to the following:

The function description for 'gdbarch_remove_non_addr_bits_memory' states:

"Given a pointer for the architecture, this hook removes all the
non-significant bits and sign-extends things as needed. It gets used to
remove non-address bits from any pointer used to access memory. "

We don't know if the pointer passed to 'gdbarch_remove_non_addr_bits_memory'
by 'gdbarch_tagged_address_p' will be used to access memory.  That's why it's
wrong to call this function in 'gdbarch_tagged_address_p'.

There are several similar wrong calls of 'gdbarch_remove_non_addr_bits_memory'
in the changes of patch 1.  I replaced all of them with
'aarch64_remove_non_address_bits'."

Regards,
Christina

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