On 12/28/16 10:05, Peter Maydell wrote: > On 28 December 2016 at 15:06, Sean Bruno <sbr...@freebsd.org> wrote: >> After some recent-ish changes to how user mode executes things/stuff, >> I'm running into issues with the out of tree bsd-user mode code that >> FreeBSD has been maintaining. It looks like the host_signal_handler() >> is never executed or registered correctly in our code. I'm curious if >> the linux-user code can handle this bit of configure script from m4. >> >> https://people.freebsd.org/~sbruno/stack.c > > Hmm. That code does: > * set up a SIGSEGV signal handler to run on its own stack > * go into an infinite recursion, expecting to run out of > stack and trigger a SEGV > which is a bit of an obscure corner case of signal handling. > > We recently fixed a lot of signal handler related bugs in linux-user > by doing a significant overhaul of that code. If bsd-user is still > using the old broken approach it's probably still got lots of bugs > in it. Alternatively, it's possible we changed some of the core > code in that process and broke bsd-user by mistake. > > Ideally all of that rework (including the support for properly > interrupting syscalls without races) should be ported over to > bsd-user at some point.
If you have a moment to point me at the merge commit that pulled in the
majority of this overhaul, I'll take a moment to review it for
application to bsd-user.
>
>> If someone has the time/inclination, can this code be compiled for ARMv6
>> and executed in a linux chroot with the -strace argument applied? I see
>> the following, which after much debugging seems to indicate that the
>> host_signal_handler() code is never executed as this code is requesting
>> that SIGSEGV be masked to its own handler.
>
> Built for ARMv7 since I don't have an ARMv6 cross compiler
> or system, but it works ok for linux (also, built with -static
> rather than run in a chroot, for convenience):
>
> e104462:xenial:qemu$ ./build/arm-linux/arm-linux-user/qemu-arm -strace
> ~/linaro/qemu-misc-tests/stack
> 29798 uname(0xf6fff1f0) = 0
> 29798 brk(NULL) = 0x0007f000
> 29798 brk(0x0007fd00) = 0x0007fd00
> 29798 readlink("/proc/self/exe",0xf6ffe328,4096) = 43
> 29798 brk(0x000a0d00) = 0x000a0d00
> 29798 brk(0x000a1000) = 0x000a1000
> 29798 access("/etc/ld.so.nohwcap",F_OK) = -1 errno=2 (No such file or
> directory)
> 29798 sigaltstack(0xf6fff2e0,(nil)) = 0
> 29798 rt_sigaction(SIGSEGV,0xf6fff1b0,NULL) = 0
> --- SIGSEGV {si_signo=SIGSEGV, si_code=1, si_addr = 0xf67ffffc} ---
> 29798 exit_group(0)
>
> (the enhancement to linux-user's strace to print the line on signal
> delivery is also a pretty new change.)
>
Thanks. This is what I expect to see.
>> https://people.freebsd.org/~sbruno/qemu-bsd-user-arm.txt
>>
>> Prior to 7e6c57e2957c7d868f74bd0d53b5e861b495e1c7 this DTRT for our
>> ARMv6 targets.
>
> This commit hash doesn't seem to be in QEMU master.
>
*sigh* ... that was the merge commit to the bsd-user branch I maintain.
Ignore it.
> thanks
> -- PMM
>
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