[Dwarf-Discuss] Proposal to reserve .debug_macro opcode 0xff

Petr Machata pmachata at redhat.com
Tue Sep 30 16:30:46 PDT 2014


Hello,

I'm working on support in elfutils for the .debug_macro proposal[1].

The numerical values and semantics of DW_MACINFO_* opcodes are
equivalent to their new-style DW_MACRO_* counterparts.  So a decoder
could transparently read in .debug_macro instead of .debug_macinfo, and
serve the opcodes found there to a client, without fear that they get
misinterpreted.

Were it not for DW_MACINFO_vendor_ext, 0xff.  This value, in new-style
sections, is part of the vendor extension block, as DW_MACRO_hi_user.
It could be allocated and emitted, and a client would misinterpret it as
DW_MACINFO_vendor_ext, decode it, and make decisions based on this
misinterpretation.

I would therefore like to propose that the opcode 0xff is considered
reserved, and DW_MACRO_hi_user is changed to 0xfe.

Does this sound reasonable?  Should I file an issue for this?

[1] http://www.dwarfstd.org/ShowIssue.php?issue=110722.1

Thanks,
Petr


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