Fix crashes in Paranoid TSO mode #4285
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Previously, many games would fail to run due to accidentally disabling TSO emulation in most instructions.
Sonicadvance1
approved these changes
Jan 20, 2025
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This PR fixes two critical issues in Paranoid TSO mode: Many applications that work with FEX's default settings would fail to run since TSO emulation wasn't enabled for most instructions. Further complications arose due to indirect memory addressing not being implemented.
A negative (but expected) side effect of fixing these issues is that Paranoid TSO mode will now make emulation unusably slow (>90% performance impact). I'm not sure there are strong enough reasons to keep around the current PTSO approach, so I wrote a patch that implements backpatching-free TSO without requiring excessive signalling. It's not included here since it's a bit more tricky to maintain at the moment, but this current PR will get things back to a functional state at least.
As a small but related side change, I realized that memcpy/memset emit slightly more
nops than needed in either TSO mode.Implementation details
The ARM instructions emitted in PTSO mode don't support indirect memory addressing (unlike the instructions emitted with backpatching-based TSO emulation), so the indirect offsets are instead manually computed using
add.