Re: [PATCH] gdb: fixes for DW_OP_entry_value when inferior is at entry point

[Andrew Burgess <aburgess@redhat.com>]

Tom Tromey <tom@tromey.com> writes:

>>>>>> "Andrew" == Andrew Burgess <aburgess@redhat.com> writes:
>
> Andrew> This fixes some issues with DW_OP_entry_value which are discussed in
> Andrew> PR gdb/34571.
>
> Thanks for doing this.
>
> Andrew> To understand the fix for this bug we need to first revisit the
> Andrew> earlier commit that introduced the bug:
>
> Andrew>   commit 1bafda2c4595f0f936a5845caf9667b70b198091
> Andrew>   Date:   Wed Apr 9 12:02:18 2025 +0200
>
> Andrew>       [gdb/symtab] Handle DW_OP_entry_value at function entry
>
> I appreciate the research and commentary as well.
>
> Looking at this code, I don't really follow why there's even such a
> large special case for trivial_entry_value.  It seems like the code
> could be much simpler: when seeing a DW_OP_entry_value, evaluate the
> entry value expression in the target frame -- either the parent frame,
> or for the trivial_entry_value case, the current frame.
>
> That is, these special checks and calls to dwarf_block_to_dwarf_reg and
> dwarf_block_to_dwarf_reg_deref (which to be clear predate the
> trivial_entry_value patch) also seem totally unnecessary, as does this
> restriction:
>
> 	    error (_("DWARF-2 expression error: DW_OP_entry_value is "
> 		     "supported only for single DW_OP_reg* "
> 		     "or for DW_OP_breg*(0)+DW_OP_deref*"));
>
> That said, I don't think there's anything wrong with an improvement that
> doesn't rewrite it all.  And anyway maybe there's some subtlety I don't
> understand.
>
> Approved-By: Tom Tromey <tom@tromey.com>

Thanks Tom.

I pushed this patch to master and gdb-18-branch.

I also have a follow on patch which is in testing now, that refactors
this code inline with your suggestion above.

I decided to push the first patch as the change here is smaller, and
especially for the gdb-18-branch, it seemed lower risk.  The refactor,
once I post it, would only be for master.

Thanks,
Andrew