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

[Tom Tromey <tom@tromey.com>]

>>>>> "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