From: "Carlos O'Donell" <carlos@redhat.com>
To: Will Newton <will.newton@linaro.org>
Cc: "Joseph S. Myers" <joseph@codesourcery.com>,
"libc-ports@sourceware.org" <libc-ports@sourceware.org>,
Patch Tracking <patches@linaro.org>
Subject: Re: [PATCH] ARM: Don't apply pointer encryption to the frame pointer
Date: Tue, 10 Dec 2013 20:11:00 -0000 [thread overview]
Message-ID: <52A77569.4070705@redhat.com> (raw)
In-Reply-To: <CANu=Dmhrc-yJZuafQXqEiJUmBv0FdGxqi2e_9iCAkr0-ob4Ozg@mail.gmail.com>
On 12/10/2013 03:05 PM, Will Newton wrote:
> On 10 December 2013 18:57, Carlos O'Donell <carlos@redhat.com> wrote:
>> On 12/10/2013 01:06 PM, Joseph S. Myers wrote:
>>> On Tue, 10 Dec 2013, Will Newton wrote:
>>>
>>>> 2013-12-10 Will Newton <will.newton@linaro.org>
>>>>
>>>> * sysdeps/arm/__longjmp.S: Don't apply pointer encryption
>>>> to fp register.
>>>> * sysdeps/arm/setjmp.S: Likewise.
>>>> * sysdeps/arm/include/bits/setjmp.h (JMP_BUF_REGLIST): Add
>>>> fp to register list, remove a4.
>>>> * sysdeps/unix/sysv/linux/arm/sysdep.h: (PTR_MANGLE_LOAD):
>>>> New macro.
>>>
>>> OK, presuming you've tested this with the glibc testsuite.
>>>
>>
>> Is it really true that ruby checks the FP?
>>
>> I don't see such code? Can you please point it out?
>
> In vm_core.h:
>
> 474 jmp_buf machine_regs;
>
> In vm.c:
>
> 1589 if (GET_THREAD() != th && th->machine_stack_start &&
> th->machine_stack_end) {
> 1590 rb_gc_mark_machine_stack(th);
> 1591 rb_gc_mark_locations((VALUE *)&th->machine_regs,
> 1592 (VALUE *)(&th->machine_regs) +
> 1593 sizeof(th->machine_regs) /
> sizeof(VALUE));
> 1594 }
>
> So it looks like a conservative GC that uses the jmp_buf as a data
> array to find potentially reachable objects. If fp contained a pointer
> to an object then the pointer encryption would render it
> undiscoverable and it would not get marked as live and could be
> collected in error.
>
> There are a number of "ifs" involved and I haven't got the testsuite
> running yet but it looks like a possibility.
>
Thanks for pointing that out.
I'll get a new glibc to the Fedora ruby maintainer and ask them to
test in parallel.
Cheers,
Carlos.
next prev parent reply other threads:[~2013-12-10 20:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-10 17:28 Will Newton
2013-12-10 18:07 ` Joseph S. Myers
2013-12-10 18:57 ` Carlos O'Donell
2013-12-10 20:05 ` Will Newton
2013-12-10 20:11 ` Carlos O'Donell [this message]
2013-12-13 15:57 ` Carlos O'Donell
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