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Re: glibc 2.19 - asyn-signal safe TLS and ASan.
- From: Kostya Serebryany <kcc at google dot com>
- To: "Carlos O'Donell" <carlos at redhat dot com>
- Cc: Paul Pluzhnikov <ppluzhnikov at google dot com>, OndÅej BÃlka <neleai at seznam dot cz>, "Joseph S. Myers" <joseph at codesourcery dot com>, Andrew Hunter <ahh at google dot com>, GNU C Library <libc-alpha at sourceware dot org>, Roland McGrath <roland at hack dot frob dot com>, address-sanitizer at googlegroups dot com
- Date: Thu, 30 Jan 2014 09:33:15 +0400
- Subject: Re: glibc 2.19 - asyn-signal safe TLS and ASan.
- Authentication-results: sourceware.org; auth=none
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On Thu, Jan 30, 2014 at 9:23 AM, Carlos O'Donell <carlos@redhat.com> wrote:
>
> On 01/29/2014 04:48 AM, Kostya Serebryany wrote:
> > [text only]
> >
> >> Indeed so, thanks!
> >> So, exporting __signal_safe_memalign&co will allow us to extend the
> >> existing hack to 2.19.
> >> If this simple change can not be done for 2.19, can *anything* be done at all?
> >> (Long term we'd still prefer something less hackish)
> >
> > FTR, I've implemented an even-uglier-then-before hack that deals with
> > dynamic TLS in both <=2.18 and 2.19.
> > So, we will survive the 2.19 release.
> > But I would appreciate if we can resolve
> > https://sourceware.org/bugzilla/show_bug.cgi?id=16291
> > before the next one (2.20).
>
> Can you please describe the hack?
intercept __tls_get_addr and __libc_memalign.
if __libc_memalign is called while we are inside __tls_get_addr, we
know we are in <= 2.18 mode and we know what to do.
if __libc_memalign was not called but the DSO ID passed to
__tls_get_addr was not seen before by the current thread,
we know that we are in 2.19 mode and that the TLS block was allocated
by __signal_safe_memalign, which
has a header with the actual block size. Ugly, as I said.
--kcc
>
> Cheers,
> Carlos.
>