Re: port-hppa/56867: hppa: intermittent SIGSEGV reports in t_ptrace_wait's stepN and setstepN test cases

[Tom Lane <tgl%sss.pgh.pa.us@localhost>]

Nick Hudson <nick.hudson%gmx.co.uk@localhost> writes:
> On 09/06/2022 06:40, Tom Lane wrote:
>> ... I found that the test passes when an ITLBMISS trap
>> occurs upon trying to execute the modified instruction stream, while
>> it fails when one does not.  That led me to guess that what's missing
>> is a TLB flush operation, and sure enough this quick-hack patch seems
>> to fix it:

> I dont this is right. The process mappings aren't changing. Will think
> about it some more.

Fair enough.  One thing worth noting is that the place where the
breakpoint instructions are being dropped is inside libc (in
_lwp_kill, where the tracee process self-SIGSTOP'd).  I have not
been able to figure out how it's okay at all to be modifying libc.
I guess that there's a copy-on-write happening somewhere so that
the traced process gets its own copy of this shared page, but
I couldn't find where that happens.  If there isn't a copy, maybe
that is a bug in itself?  If there is a copy, then the process
mapping *is* changing, although you'd think the COW code would
have dealt with it.

			regards, tom lane