On 4 December 2011 12:17, Avi Kivity <a...@redhat.com> wrote: > On 12/02/2011 04:49 PM, Peter Maydell wrote: >> However what I found is that the addresses passed to the read/write >> functions aren't what I would expect. For instance if the board >> maps the container at address 0x1e000000, then a read from 0x1e000100 >> goes to the functions given by a9_gic_cpu_ops, as it should. However, >> the offset parameter that the read function is passed is not 0x0 >> (offset from the start of the a9mp-gic-cpu region) but 0x100 (offset >> from the start of the page, I think). >> >> Is this expected behaviour? I certainly wasn't expecting it... > > A while ago this was the behaviour across the board. Then 8da3ff1809747 > changed addresses to be relative, but apparently missed the subpage case.
Having looked a bit more closely at the code I think this is what the comment at the top of cpu_register_physical_memory_log() is referring to: # Both start_addr and region_offset are rounded down to a page boundary # before calculating this offset. This should not be a problem unless # the low bits of start_addr and region_offset differ. In the case of a subregion at a non-page-aligned-address the start_addr is not page aligned, but the region_offset is zero, in the usual case, so we have differing low bits. >> I looked through the code that's getting called for reads, and >> it looks to me like exec.c:subpage_readlen() is causing this. >> We look up the subpage_t based on the address within the page, >> but we don't then adjust the address we pass to io_mem_read >> (except by region_offset, which I take from the comment at the >> top of cpu_register_physical_memory_log() to be for something >> else.) > I think you can use subpage_t's region_offset array for this (adding > into it, of course, so the original value remains). Yes. I think the correction has to be calculated and applied in cpu_register_physical_memory_log() -- for a region which starts at a non-page-aligned address and extends over more than a page the correcting offset needs to be applied for the whole region, not just the first partial page. -- PMM