gas: encoding of cv.ext* and hardware loop constants - Githubissues

openhwgroup / corev-binutils-gdb

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gas: encoding of cv.ext* and hardware loop constants #36

Closed bluewww closed 2 years ago

bluewww commented 3 years ago

A while ago I rewrote and ported the pulp gcc and pulp binutils to a newer gcc release. I imported the new tests that were added to the assembler and I found a few discrepancies:

From https://cv32e40p.readthedocs.io/en/latest/instruction_set_extensions/#general-alu-encoding

cv.extbs t0,t1 is encoded as 0x040362b3, but I think this should be 0x100362b3. The 28-th bit (counting from zero) should be 1. (python -c 'print(0x100362b3 >> 28 & 1)'). Similar issue with the other ext* instructions.

From https://cv32e40p.readthedocs.io/en/latest/instruction_set_extensions/#hardware-loops

In the assembler and in the test cv-hwlp-fail-operand-01.s it assumes that the branch offset must be an even integer in [0, 4094]. Looking at the encoding though (12-bit unsigned immediate) it seems to me the range should be an even integer in [0, 8190]

Robert

jessicamills commented 2 years ago

@bluewww Thank you for the bug report and the reproducer. We will look in to this and keep you updated.