| 1 |
On Tue, Nov 14, 2017 at 11:36 AM, Jorge Almeida <jjalmeida@×××××.com> wrote: |
| 2 |
> On Fri, Nov 10, 2017 at 12:09 PM, Jorge Almeida <jjalmeida@×××××.com> wrote: |
| 3 |
> |
| 4 |
>> http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html |
| 5 |
>> |
| 6 |
>> |
| 7 |
>>>> Of course, what would really solve the optimize-into-oblivion problem |
| 8 |
>>>> is a pragma that when invoked on a particular block of code (maybe |
| 9 |
>>>> only a function definition) would tell the compiler to do what the |
| 10 |
>>>> programmer says rather than viewing a function as a kind of black box. |
| 11 |
>>>> |
| 12 |
>>> |
| 13 |
> |
| 14 |
> It seems a solution exists with gcc: |
| 15 |
> |
| 16 |
> https://stackoverflow.com/questions/2219829/how-to-prevent-gcc-optimizing-some-statements-in-c |
| 17 |
> |
| 18 |
> The last reply: |
| 19 |
> |
| 20 |
> void __attribute__((optimize("O0"))) foo(unsigned char data) { |
| 21 |
> // unmodifiable compiler code |
| 22 |
> } |
| 23 |
> |
| 24 |
> Any comments, anyone? Yes, it's gcc, but IMO this should be in the |
| 25 |
> language itself. Am I right to assume this is a poorly known feature |
| 26 |
> of gcc? |
| 27 |
> It allows, for example, to replace sensitive data by random bytes, |
| 28 |
> existing system callls like memset() or getrandom() can be used as |
| 29 |
> they are, no reimplementation needed. |
| 30 |
> |
| 31 |
|
| 32 |
Very interesting. I imagine the opinion of the standards committee |
| 33 |
would be that the variability in code generation precludes a standard |
| 34 |
interface to optimization controls. This might seem unusual, but |
| 35 |
languages with a very controlling standard (like Java or C#) are a new |
| 36 |
concept. |
| 37 |
|
| 38 |
What I am wondering about is if C code which uses |
| 39 |
__attribute__((optimize(...))) is against Gentoo package standards and |
| 40 |
would have to be removed from the Portage tree. |
| 41 |
|
| 42 |
Cheers, |
| 43 |
R0b0t1 |
Archives