I've written a DWARF expression parser and stack unwinder and its not true that those three use-cases are enough to be robust [0]. Based on my own observations, you need to implement:
- undefined
- same value
- offset(N)
- val_offset(N)
- register(N)
I've never come across expression(E), val_expression(E), or architectural. But you definitely do need the above in the common cases.
More generally, I'm kinda confused by that quote, I think the author may be conflating DWARF expressions and stack unwinding a bit?
What I think they might have been getting at is that with DWARF expression evaluation [1] in particular (i.e. not just stack unwinding), I've never even seen +80% of the opcodes I've implemented in the wild across several programming languages and compilers. I also left about 1/4 of them unimplemented and I've never had an issue. The intention of the DWARF spec writers was to provide folks with a stack machine that was Turing-complete, but in practice, yeah, nobody really takes advantage of it because there's not really a need.
[0] https://dwarfstd.org/doc/DWARF5.pdf (section 6.4)
[1] https://dwarfstd.org/doc/DWARF5.pdf (section 7.7)
- undefined - same value - offset(N) - val_offset(N) - register(N)
I've never come across expression(E), val_expression(E), or architectural. But you definitely do need the above in the common cases.
More generally, I'm kinda confused by that quote, I think the author may be conflating DWARF expressions and stack unwinding a bit?
What I think they might have been getting at is that with DWARF expression evaluation [1] in particular (i.e. not just stack unwinding), I've never even seen +80% of the opcodes I've implemented in the wild across several programming languages and compilers. I also left about 1/4 of them unimplemented and I've never had an issue. The intention of the DWARF spec writers was to provide folks with a stack machine that was Turing-complete, but in practice, yeah, nobody really takes advantage of it because there's not really a need.
[0] https://dwarfstd.org/doc/DWARF5.pdf (section 6.4) [1] https://dwarfstd.org/doc/DWARF5.pdf (section 7.7)