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[Bug 1903833] Re: User mode qemu-aarch: SIGGSEGV signal handler works wr

From: Richard Henderson
Subject: [Bug 1903833] Re: User mode qemu-aarch: SIGGSEGV signal handler works wrong
Date: Thu, 12 Nov 2020 21:37:50 -0000

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.

** Changed in: qemu
       Status: New => Incomplete

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  User mode qemu-aarch: SIGGSEGV signal handler works wrong

Status in QEMU:

Bug description:
  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:

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

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