On Sat, Mar 19, 2011 at 04:43:46PM +0100, thus spake Christian Lamparter: > On Saturday 19 March 2011 10:22:37 Ignacy Gawedzki wrote: > > As a rule of thumb, I remembered that "volatile" tells the compiler "you're > > not the only one to manage that variable, don't make any assumptions about its > > current value", as could be the case if the variable is allocated in some > > shared memory segment/register/whatever and might change "on its own". > > Anyway, in the case at hand, it seems to make a difference. > > why not give it a try ;). define a and b as global variables, initialize them > and try if a/b needs __udiv or not. you'll be surprised that no c-compiler > (unless a buggy one) will even think about this sort of "constant" > optimization. I almost forgot to reply to this one. Of course you were right and optimizing globals in this way doesn't make sense anyway. After noticing the unexpected behavior, I disassembled the object file and saw that the result of the division was used as an immediate value. Eventually, after this round of email exchange, I realized that it was all due to my globals being declared as "static", just for the sake of uniformity with other globals already there. =) When globals' scope is limited to the compilation unit, the compiler may optimize things out. > OT: the use of volatile is ill-reputed and many people have complained > about it throughout the history. > http://lwn.net/Articles/233482/ [which ended up in:] > http://kernel.org/doc/Documentation/volatile-considered-harmful.txt > > the only reason why we get away with it is because most of > it is locked up behind accessor functions in include/io.h & dma.h > and it should remain that way. > > > BTW, it seems you have some detailed technical documentation about the AR9170 > > at your disposal. I was wondering whether this is something available > > publicly or not. Could be an interesting read at times. =) > There are a lot of easy accessible docs about the CPU on the net. In fact you > can even get Verilog/VHDL code of various SH2-clones without any problem. > But that's about it, for information about the MAC/USB I have to rely on > Chen. I see. Thanks again. Ignacy -- NO CARRIER -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
