- Forget about C++, C is not a low-level language either - 2 Updates
- Template friend of templated class - 2 Updates
| scott@slp53.sl.home (Scott Lurndal): May 28 01:23PM >> flushing the cache is a side effect of the exception, thus a covert >> channel - useful to determine valid kernel addresses, for example. >You get an exception when you access a page that you're not allowed to. Which, of course, takes longer than an access that doesn't get an exception. Covert channel #1. >System flushes the cache. Which, of course, changes the timing of the code that executes following the flush. Covert channel #2. >There is no way to determine whether this is an illegal address, or a >forbidden address - unless of course the system chooses to tell you. Doesn't matter. It's information that can be used. >What will you do with the list of valid kernel addresses anyway? It's >their contents that are interesting. What the list of valid kernel addresses provides is information. Useful information to those attempting to subvert the kernel; and certainly key to the exploits enabled by Spectre/Meltdown. Amongst other things, it allows the attacker to subvert KASLR. |
| Robert Wessel <robertwessel2@yahoo.com>: May 28 11:36AM -0500 On Sun, 27 May 2018 21:26:15 +0100, Vir Campestris >Without C, yes. Or Fortran, Cobol, Algol... maybe APL would like a >properly parallel machine, but I can't think of another language of that >vintage that isn't essentially single threaded. IBM's PL/1 supporting threading (with a fork/join sort of mechanism on subroutine calls) in 1966 (and still does), although that was not a feature that made it into the standard. |
| Juha Nieminen <nospam@thanks.invalid>: May 28 09:29AM This compiles ok: //------------------------------------------------------------ struct Test { template<typename T> friend Test friendFunc(T); private: int value; }; template<typename T> Test friendFunc(T value) { Test test; test.value = value; return test; } int main() { friendFunc(10); } //------------------------------------------------------------ However, this does not: //------------------------------------------------------------ template<typename R> struct Test { template<typename T> friend Test<R> friendFunc(T); private: int value; }; template<typename T> Test<T> friendFunc(T value) { Test<T> test; test.value = value; return test; } int main() { friendFunc(10); } //------------------------------------------------------------ It complains that the member variable is private. How to make the second example compile as well? |
| Chris Vine <chris@cvine--nospam--.freeserve.co.uk>: May 28 11:07AM +0100 On Mon, 28 May 2018 09:29:04 -0000 (UTC) > //------------------------------------------------------------ > It complains that the member variable is private. > How to make the second example compile as well? If you change the friendship declaration of friendFunc in Test to: template<typename T> friend Test<T> friendFunc(T); so that it matches the definition, it will compile. The templatizing of Test on R is pointless and presumably you really want the 'value' member to be of type R? Chris |
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