CLRV macro sets C

Why does this macro set C on the Pi build? It encodes to the following (spotted in Finalise_Module of SoundDMA):

MSR CPSR_f,#&20000000

Is that a bug or by design?

It’s intentional. The original 26bit version does CMP PC,#0, which would result in nzCv being set. To avoid any potential side-effects the 32bit version is careful to copy the behaviour exactly.

The original 26bit version does CMP PC,#0, which would result in nzCv being set

Ah, that may be the reason why some OS_Byte mysteriously set C.

EDIT: My notes on OS_Byte C flag corruption, from a partial check of behaviour in RISCOS 3.11:

0..4 – clear C
5 – sets C
6..19 – clear C
20 – sets C
21 – clears C
25 – sets C
70..71 – set C
106..117 – clear C
118..120 – set C
121 – clears C
122 – sets C
124..128 – clear C
129,0,255 – clears C
129,1,0 – sets C
129,128,255 – clears C
134..135 – set C

Ah, that may be the reason why some OS_Byte mysteriously set C.

Sometimes that’s done on purpose to flag something happened, like key was pressed…