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Data processing instructions with a shift by register where rs == 15 seem to be broken #1926

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wheremyfoodat opened this issue Oct 31, 2020 · 1 comment
Closed

Data processing instructions with a shift by register where rs == 15 seem to be broken #1926

wheremyfoodat opened this issue Oct 31, 2020 · 1 comment

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@wheremyfoodat
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If rs == r15, the pc should still be (addr of instruction + 8), not +12.
In the .zip below, I've included a test ROM + source code for this edge case.

If the shift is by (addr of instruction + 8), the ROM displays green.
If it's +12, the ROM displays blue.
Else, it displays red.

The version of mgba I've installed displays blue, while the 3DS displays green

shift_test.zip
@endrift
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endrift commented Nov 1, 2020

Good catch. Looks like I misread GBATEK a long time ago and never caught that it was a bug.

@endrift endrift closed this as completed in a53b01b Nov 1, 2020
endrift added a commit that referenced this issue Nov 5, 2020
@endrift
ARM: Fix Addressing mode 1 shifter on rs == pc (fixes #1926)
9c321c3
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@endrift @wheremyfoodat