On Fri, 2009-11-20 at 09:04 +0300, stas wrote: > It seems to me that this example code is not free of errors. After the > third ":" we should list registers "ebx" and "ecx" to let gcc know > they could change in asm section. > > __asm__ volatile ( > "movl (%0), %%ebx\n\t" > "movl (%1), %%ecx\n\t" > "outl %%ebx, $0xb2\n\t" > "outl %%ecx, $0xb6\n\t" > > > : > : "r"(var_a), "r"(var_b) > : "ebx", "ecx" That's not good enough. Because the compiler could choose to use %ebx for passing in 'var_b', and then it would get clobbered before you move it to %ecx in the second instruction. You'd need to make it an earlyclobber too. > > The SAME code: > __asm__ volatile ( > "outl %%ebx, $0xb2\n\t" > "outl %%ecx, $0xb6\n\t" > : > : "b"(var_a), "c"(var_b) > ); That's the better approach, although yours didn't do what Johnny's original seemed to. Jiri Slaby posted something which looks correct. > /* taken from linux-2.6./include/asm-generic/io.h > If you want to use it in user-space just replace u8 with unsigned char, > u16 with unsigned short. In kernel space just insert #include directive. > */ > static inline void outb(u8 v, u16 port) And that's just an entirely gratuitous use of our kernel nonsense-types. Just use the proper C types uint16_t and uint8_t instead. Or just 'unsigned char' and 'unsigned short', for that matter -- I believe Linux would blow up horribly if those types ever changed from 8-bit and 16-bit respectively. -- dwmw2 -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
