On Mon, Mar 4, 2013 at 6:46 PM, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote: > On 4 March 2013 23:40, Jeffrey Walton wrote: >> Hi All, >> >> I was looking at some slides on OpenSSL and secure memory wiping using >> volatile (Slide 36 at >> http://www.slideshare.net/guanzhi/crypto-with-openssl). >> >> I believe GCC's interpretation of the use for 'volatile' is memory >> mapped hardware. I think Ian stated it for me some time ago when I was >> trying to understand different interpretations among compilers. If >> volatile is for memory mapped hardware, why does GCC compile the >> following: >> >> volatile void clean_memory(volatile void* dest, size_t len) >> { >> volatile unsigned char* p; >> for(p = (volatile unsigned char*)dest; len; dest[--len] = 0) >> ;; >> } > > This doesn't compile, it dereferences void. Did you mean p[--len] ? Yes, my bad. Sorry - copy[paste was not available because the slide was an umage. >> How does a function become a 'volatile' memory mapped object related >> to hardware? > > The function isn't volatile, the return type is. Qualifying void as > volatile is meaningless, but allowed by the C grammar. :) Jeff
