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Re: Preventing preemption of 'protected' symbols in GNU ld 2.26 [aka should we revert the fix for 65248]
- From: Alan Modra <amodra at gmail dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: "H.J. Lu" <hjl dot tools at gmail dot com>, Jeff Law <law at redhat dot com>, Cary Coutant <ccoutant at gmail dot com>, Joe Groff <jgroff at apple dot com>, Binutils <binutils at sourceware dot org>, GCC <gcc at gcc dot gnu dot org>
- Date: Tue, 19 Apr 2016 00:19:11 +0930
- Subject: Re: Preventing preemption of 'protected' symbols in GNU ld 2.26 [aka should we revert the fix for 65248]
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- References: <983472E1-A1BC-4970-9CF9-0138A6BAD16D at apple dot com> <CAMe9rOqTTwirymAY6ORp6D_GnCsMc_hYEdy1NbZpG6x5vQc5DQ at mail dot gmail dot com> <6AAD87D2-90F9-4AD7-A195-AC91B76EA6AE at apple dot com> <CAMe9rOqNcYnm1YocG-m7XNDE0g68YQAGe=ULP-G98gaatpxSeA at mail dot gmail dot com> <CAJimCsHfT=cfb4kZysB2W_1HFfOq==TpP=wa47XPGB41MHmGyQ at mail dot gmail dot com> <56FB5061 dot 9010303 at redhat dot com> <20160330143421 dot GM15812 at bubble dot grove dot modra dot org> <571161D0 dot 10601 at redhat dot com> <CAMe9rOpt2Fd6RLtjr10wCHz9PVsXxtO9a0yvMR_DeHt1OK0ieg at mail dot gmail dot com> <CAFiYyc2PFQdiUj=UPY8HLv+PjwVaNpcvDW6Skp8JC4DR56MkBg at mail dot gmail dot com>
On Mon, Apr 18, 2016 at 11:01:48AM +0200, Richard Biener wrote:
> To summarize: there is currently no testcase for a wrong-code issue
> because there is no wrong-code issue.
That depends entirely on how far you are willing to bend the ELF gABI.
Any testcase the takes the address of a protected visibility variable
defined in a shared library now can get the wrong answer, since you
can argue that any address outside the shared library is wrong
according to the gABI.
I expect you can also write a testcase using a const protected var in
a shared library that ought to segfault on writing to the var from
code within the shared library, that now merrily writes to a .dynbss
copy.
--
Alan Modra
Australia Development Lab, IBM