On Tue, 18 Jan 2022 at 23:30, Andre Przywara <andre.przyw...@arm.com> wrote: > Looking at k-u-t's arm/gic.c and QEMU's hw/intc/arm_gic.c I see two > problems here: QEMU implements word accesses as four successive calls to > gic_dist_readb() - which is probably fine if that helps code design, > but it won't allow it to actually spot access size issues. I just > remember that we spent some brain cells and CPP macros on getting the > access size right in KVM - hence those tests in kvm-unit-tests.
Thanks for looking at this. I should have read the code rather than dashing off a reply last thing in the evening based just on the test case output! I think I was confusing how our GICv3 emulation handles register accesses (with separate functions for byte/halfword/word/quad accesses) with the GICv2 emulation (which as you say calls down into the byte emulation code wherever it can). > But more importantly it looks like GICD_IIDR is actually not > implemented: There is a dubious "if (offset < 0x08) return 0;" line, > but IIDR (offset 0x8) would actually fall through, and hit the bad_reg > label, which would return 0 (and cause the message, if enabled). Mmm. I actually have a patch in target-arm.next from Petr Pavlu which implements GICC_IIDR, but we do indeed not implement the distributor equivalent. > If that helps: from a GIC MMIO perspective 8-bit accesses are actually > the exception rather than the norm (ARM IHI 0048B.b 4.1.4 GIC register > access). Yes. We got this right in the GICv3 emulation design, where almost all the logic is in the 32-bit accessor functions and the 8/16-bit functions deal only with the very few registers that have to permit non-word accesses. The GICv2 code is a lot older (and to be fair to it, started out as 11MPcore interrupt controller emulation, and I bet the docs of that were not very specific about what registers could or could not be accessed byte at a time). Unless we want to rewrite all that logic in the GICv2 emulation (which I at least do not :-)) I think we'll have to live with the warnings about bad-offsets reporting for each byte rather than just once for the word access. -- PMM
