quemu-user 32-bit fixes in support of building Proton in linux/amd64 containers on non-Intel hosts - #350
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…around. mmap_add_reserved_area() and mmap_remove_reserved_area() trim a single byte when addr + size wraps to 0, leaving an area whose end is 0xffffffff. alloc_virtual_heap() derives its mapping address from that end and passes an unaligned address to anon_mmap_fixed(), tripping the alignment assertions added in d813ffc. Trim a whole page instead so the area bounds stay aligned. Only reached when a reserved area ends exactly at 4GB, which requires mmap_init() to take the reserve_area( user_space_limit, 0 ) branch -- that is, when the initial stack is not near the top of the 32-bit address space. Native Linux places it near the top so the branch is dead there; qemu-user maps the 32-bit stack around 0x40000000, making it reachable and aborting every 32-bit process at startup. This is hit when building or running Proton in a container on an arm64 host, where 32-bit x86 goes through qemu-user. Submitted upstream separately. Signed-off-by: Nat Brown <natbro@gmail.com>
… one. qemu-user synthesizes signal frames without filling in the trap number, leaving TRAP_sig() as -1. segv_handler() falls through to the default case, logs "Got unexpected trap -1" and never services the fault, so page faults during 32-bit module loading surface as unhandled exceptions. Infer the trap from the delivered signal. ERROR_sig() is unset for the same reason, so faults routed to TRAP_x86_PAGEFLT are classified as reads; enough to get through process startup but not a complete emulation of the missing context. Submitted upstream separately. Signed-off-by: Nat Brown <natbro@gmail.com>
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Hello @natbro, this should be reviewed and merged upstream first. After it's landed, leave a note here with a link to the commit and a Proton dev can ponder a backport. |
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will do, somehow thought order-of-operations was reversed. slightly different upstream, so I'll note that and reference that merge request shortly. |
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FYI - this is in support of ValveSoftware/Proton#10087 |
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two minor latent issues found when running 32-bit wine in linux/amd64 containers when the host uses qemu-user for 32-bit processes, such as Docker or Podman using Apple Virtualization on Apple Silicon (x86_64 is run via Rosetta 2, i386 is handled by qemu). Individual commits have further documentation.