User mode qemu-aarch: SIGGSEGV signal handler works wrong

[Boris]

I have a user mode qemu-aarch issue. Program with SIGSEGV signal handler works wrong under qemu-aarch:
once the progam handles the SEGV signal, qemu marks the program's page protected, and signal handler gets SEGV on each subsequent memory access instruction within a program.

The issue is reproduced on WSL Ubuntu 20.04 under Windows 10, qemu-aarch64 version 5.1.50
The issue is also reproducible on the latest upstream qemu-aarch build.

The following workaround disables mprotect call and fixes the issue: https://github.com/BorisUlasevich/qemu/commit/3063d9a64f8395185d65c6b6710d28ee92cd8be5

The issue can be reproduced on OpenJDK which reports SIGSEGV immediately after start. The small reproducer program is attached.

[Richard Henderson (rth)]

The patch is most definitely wrong. The page protection
is required to implement self-modifying code, of which a
signal trampoline is a subset.

Moreover, your test case works for me using both
x86_64-linux and aarch64-linux as hosts.

There may be a bug, but I suspect it to be within WSL.
I have no way to test that one way or another.

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]