Unexpected Dynarec-Interpreter Difference on `cmp` Instruction about box64 HOT 4 CLOSED

A good first step would be to dump the instructions the dynarec produces: BOX64_DYNAREC_DUMP=2 BOX64_TRACE=0-1 BOX64_TRACE_FILE=dump.txt <program>, then looking at the problematic addresses (note that the trace build* is quite helpful in this case). Note that BOX64_DYNAREC_TEST adds quite a lot of clutter, so if you can't see the issue you can try again with that option.
Also, a DUMP of 2 will add color (ANSI escape codes) to the output (you can read it using less -R). If you want to open it in a text editor, this will make the file much less readable; in this case, you should instead use a DUMP of 1.

*The trace build requires libzydis version v3.2.1: https://github.com/zyantific/zydis/tree/v3.2.1 (newer versions change the API).

from box64.

A bit of context about what those ADJUST FLAG11 do:
One of the x86 flags OF is on bit 11 of the xFlags. But on RV64, most (all?) operation that use an Immediate have a signed 12bits immediate. That means, if trying to use an immediat to set this bit, the value will get sign extensed (because bit 11 is the sign bit for a 12bit signed value).
To avoid more opcode when setting this bit (that is set/unset often), it's moved to a different place inside RV64 dynarec (one of the lower reserved bit, the F_OF2 macro). And it works fine (and quite fast). The olnly issue is when exchanging the flags register outside of the Dynarec: those ADJUST macro allow to swap/unswap this bit in place.

from box64.

@rajdakin Thanks for your hints. I further investigated the code and found these differences only occured when I used BOX64_DYNAREC_TEST=1. I saw this code:

When I removed the FLAGS_ADJUST_TO11 & FLAGS_ADJUST_FROM11, python3.12 could run without any dynarec-interpreter differences even if I enabled BOX64_DYNAREC_TEST=1. Honestly, I don't know why we need FLAGS_ADJUST_* here, but I just suspected them doing something unexpected to the FLAGS.

from box64.

A bit of context about what those ADJUST FLAG11 do: One of the x86 flags OF is on bit 11 of the xFlags. But on RV64, most (all?) operation that use an Immediate have a signed 12bits immediate. That means, if trying to use an immediat to set this bit, the value will get sign extensed (because bit 11 is the sign bit for a 12bit signed value). To avoid more opcode when setting this bit (that is set/unset often), it's moved to a different place inside RV64 dynarec (one of the lower reserved bit, the F_OF2 macro). And it works fine (and quite fast). The olnly issue is when exchanging the flags register outside of the Dynarec: those ADJUST macro allow to swap/unswap this bit in place.

Thanks for your attention on this issue. And I now fully understand why we need these macros.

from box64.