id = 1361
title = "ppc64le linux user emulation w/ 64KiB pages seems broken since v5.0.0"
state = "opened"
created_at = "2022-12-11T07:09:13.156Z"
closed_at = "n/a"
labels = ["linux-user", "target: ppc"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1361"
host-os = "Various Linux (Ubuntu, Debian under WSL)"
host-arch = "x86"
qemu-version = "See below"
guest-os = "Linux"
guest-arch = "ppc64el"
description = """[Our (snmalloc's)](https://github.com/microsoft/snmalloc) CI includes running a PowerPC64 little-endian Linux build inside qemu, running with 64KiB pages as, at least, Debian runs them by default.  As reported [over there](https://github.com/microsoft/snmalloc/issues/576), this broke when GitHub's CI runners moved from Ubuntu Focal (20.04) to Jammy (22.04), bringing qemu from v4.2 to v6.2.

The failing test case appears to die of an erroneous `SIGSEGV` `SEGV_MAPERR`:
```
--- SIGSEGV {si_signo=SIGSEGV, si_code=1, si_addr=0x0000004001be5000} ---
```
despite that address nominally being mapped by the last memory syscall to touch that area
```
openat(AT_FDCWD,"/usr/powerpc64le-linux-gnu/lib/libstdc++.so.6",O_RDONLY|O_CLOEXEC) = 4
[...]
mmap(0x0000004001bd0000,131072,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_DENYWRITE|MAP_FIXED,4,0x2f0000) = 0x4001bd0000
```

Bisection reveals that the breakage first occurred with 4dcf078f094d436866ef793aa25c96fba85ac8d0, though I suspect this is merely the commit that exposes some underlying bug rather than being the actual root cause."""
reproduce = """Run a ppc64el Linux executable under `qemu-user` with `-p 65536`."""
additional = """Please advise what more would be useful."""