On Tue, Nov 14, 2017 at 8:42 PM, R0b0t1 <r03...@gmail.com> wrote: > On Tue, Nov 14, 2017 at 11:36 AM, Jorge Almeida <jjalme...@gmail.com> wrote: >> On Fri, Nov 10, 2017 at 12:09 PM, Jorge Almeida <jjalme...@gmail.com> wrote: >> >>> http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html >>> >>> >>>>> Of course, what would really solve the optimize-into-oblivion problem >>>>> is a pragma that when invoked on a particular block of code (maybe >>>>> only a function definition) would tell the compiler to do what the >>>>> programmer says rather than viewing a function as a kind of black box. >>>>> >>>> >> >> It seems a solution exists with gcc: >> >> https://stackoverflow.com/questions/2219829/how-to-prevent-gcc-optimizing-some-statements-in-c >> >> The last reply: >> >> void __attribute__((optimize("O0"))) foo(unsigned char data) { >> // unmodifiable compiler code >> } >> >> Any comments, anyone? Yes, it's gcc, but IMO this should be in the >> language itself. Am I right to assume this is a poorly known feature >> of gcc? >> It allows, for example, to replace sensitive data by random bytes, >> existing system callls like memset() or getrandom() can be used as >> they are, no reimplementation needed. >> > > Very interesting. I imagine the opinion of the standards committee > would be that the variability in code generation precludes a standard > interface to optimization controls. This might seem unusual, but > languages with a very controlling standard (like Java or C#) are a new > concept.
Well, we'll have to stick to gcc (or other compilers with the same feature). OTOH, boldness doesn't seem to be the comittee's most salient feature. > > What I am wondering about is if C code which uses > __attribute__((optimize(...))) is against Gentoo package standards and > would have to be removed from the Portage tree. > You can set your optimization preferences in make.conf, and still an ebuild will override them if deemed unsafe. What would be the difference? Cheers Jorge
