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Re: [PATCH] ARM: Don't apply pointer encryption to the frame pointer
- From: Will Newton <will dot newton at linaro dot org>
- To: "Carlos O'Donell" <carlos at redhat dot com>
- Cc: "Joseph S. Myers" <joseph at codesourcery dot com>, "libc-ports at sourceware dot org" <libc-ports at sourceware dot org>, Patch Tracking <patches at linaro dot org>
- Date: Tue, 10 Dec 2013 20:05:38 +0000
- Subject: Re: [PATCH] ARM: Don't apply pointer encryption to the frame pointer
- Authentication-results: sourceware.org; auth=none
- References: <52A74F24 dot 8000805 at linaro dot org> <Pine dot LNX dot 4 dot 64 dot 1312101806240 dot 15324 at digraph dot polyomino dot org dot uk> <52A7641C dot 7020400 at redhat dot com>
On 10 December 2013 18:57, Carlos O'Donell <email@example.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 <firstname.lastname@example.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?
474 jmp_buf machine_regs;
1589 if (GET_THREAD() != th && th->machine_stack_start &&
1591 rb_gc_mark_locations((VALUE *)&th->machine_regs,
1592 (VALUE *)(&th->machine_regs) +
1593 sizeof(th->machine_regs) /
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.
Toolchain Working Group, Linaro