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Re: Should glibc be fully reentrant? -- No. (Roland was right).
- From: Florian Weimer <fweimer at redhat dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: "Carlos O'Donell" <carlos at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>, Roland McGrath <roland at hack dot frob dot com>, Siddhesh Poyarekar <siddhesh at redhat dot com>
- Date: Mon, 15 Dec 2014 09:52:52 +0100
- Subject: Re: Should glibc be fully reentrant? -- No. (Roland was right).
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- References: <5488F9C6 dot 9080605 at redhat dot com> <54898FE0 dot 8060701 at redhat dot com> <20141211133353 dot GB10717 at domone> <5489A11A dot 3080300 at redhat dot com> <20141211141136 dot GA17090 at domone> <548ABA5B dot 9090002 at redhat dot com> <20141212161750 dot GA22945 at domone>
On 12/12/2014 05:17 PM, OndÅej BÃlka wrote:
On Fri, Dec 12, 2014 at 10:50:19AM +0100, Florian Weimer wrote:
On 12/11/2014 03:11 PM, OndÅej BÃlka wrote:
Yes, I wrote that from head so I forgot volatile/asm barrier. One could
add requirement like needs to be compiled by gcc4-6+ instead pure C as
just using signals is not part of C standard.
GCC emulates atomics with locks on some platforms, or some lock-free
instruction sequences may not be reentrant. This begins to look
like a can of worms, unfortunately.
It uses only thread local variable. If they are not reentrant its
gigantic hole, you could not for example use sigaction as it could
set errno which is thread local variable.
Sorry, what I'm trying to say is that atomics are not specified as
async-signal-safe, and some actually aren't in practice.
Florian Weimer / Red Hat Product Security