This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: TLS redux
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Rich Felker <dalias at aerifal dot cx>, Jason Evans <jasone at canonware dot com>
- Cc: Paul Pluzhnikov <ppluzhnikov at google dot com>, Andreas Schwab <schwab at linux-m68k dot org>, "Joseph S. Myers" <joseph at codesourcery dot com>, Roland McGrath <roland at hack dot frob dot com>, "GNU C. Library" <libc-alpha at sourceware dot org>, Will Newton <will dot newton at linaro dot org>
- Date: Thu, 30 Jan 2014 00:45:31 -0500
- Subject: Re: TLS redux
- Authentication-results: sourceware.org; auth=none
- References: <20140115022335 dot EB13174430 at topped-with-meat dot com> <Pine dot LNX dot 4 dot 64 dot 1401150520530 dot 14350 at digraph dot polyomino dot org dot uk> <CALoOobOyQxDaszErqoOkSdHsc7NestF7Pt9rS01aPzWZcnFZCQ at mail dot gmail dot com> <87r47tz5xd dot fsf at igel dot home> <CALoOobNZVFQ7z0uOgp6zAKMk7fmx03ua6S5E24UNgtVM3o=etQ at mail dot gmail dot com> <61CF7641-148C-4D7B-BE80-A1E3CC0AA498 at canonware dot com> <20140129012316 dot GM24286 at brightrain dot aerifal dot cx>
On 01/28/2014 08:23 PM, Rich Felker wrote:
> On Mon, Jan 27, 2014 at 11:25:27AM -0800, Jason Evans wrote:
>> On Jan 27, 2014, at 9:52 AM, Paul Pluzhnikov <ppluzhnikov@google.com> wrote:
>>> On Mon, Jan 27, 2014 at 9:32 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>>>
>>>>> One example that's burned into my memory is that memory allocated by
>>>>> ld.so's private malloc may later be free'd by public libc.so.6 free.
>>>>
>>>> That should not happen, and would be a major bug.
>>>
>>> I could be mistaken, but I am 99% sure this *did* happen in glibc-2.2
>>> - 2.5 time frame under specific (and rare) execution path with
>>> pthread_exit from main thread or some such.
>>>
>>>>> They are the same implementation, so no harm done, right?
>>>>
>>>> The ld.so malloc is a stub implementation that has nothing in common
>>>> with libc malloc.
>>>
>>> Currently that's the case. Was that the case in glibc-2.2?
>>>
>>>
>>> Anyway, my point is that interposing malloc under glibc was never an
>>> easy affair, was fraught with special cases, and Roland's claim that
>>> we broke it by using different allocator for TLS is an
>>> over-simplification of the reality that tools like Leak Sanitizer face
>>> now (and will likely continue to face for a while).
>>
>> Here's a slight variation on how the non-hermetic ld.so design can
>> bite:
>>
>> http://www.canonware.com/pipermail/jemalloc-discuss/2013-November/000663.html
>>
>> In short, ld.so doesn't save/restore floating point state when
>> calling into malloc, which can corrupt application state as a side
>> effect of lazy symbol loading.
>
> Yet another reason that failing to save/restore the FULL register set
> on lazy symbol resolution is a bug that should be fixed on all archs,
> rather than being swept under the rug with excuses.
Do we have a bugzilla entry for this?
I can tag it for 2.20 and see if we can fix this.
The consequences seem somewhat dire though for performance?
Could we just do the save/restore around malloc at least?
I thought we ran into a similar bug for ARM and NEON?
Cheers,
Carlos.