Re: [PATCH 08/10] m68k: Add

George Spelvin
2016-05-25T09:14:37Z

> On Wed, May 25, 2016 at 03:34:55AM -0400, George Spelvin wrote:
>> +static inline u32 __attribute_const__ __hash_32(u32 x)
>> +{
>> + u32 a, b;
>> +
>> + asm( "move.l %2,%0" /* 0x0001 */
>> + "\n lsl.l #2,%0" /* 0x0004 */
>> + "\n move.l %0,%1"
>> + "\n lsl.l #7,%0" /* 0x0200 */
>> + "\n add.l %2,%0" /* 0x0201 */
>> + "\n add.l %0,%1" /* 0x0205 */
>> + "\n add.l %0,%0" /* 0x0402 */
>> + "\n add.l %0,%1" /* 0x0607 */
>> + "\n lsl.l #5,%0" /* 0x8040 */
>> + /* 0x8647 */

> There is no standard way to write asm in the kernel, but I prefer
> a simple semicolon after each insn

I did it the way I did above because it makes the gcc -S output very
legible. Just like I put a space before the perands on m68k but a tab
on h8300: that's what GCC does on those platforms.

I started with the "\n\t" suffixes on each line like so much other
kernel code, but then figured out the format above which is legible
both in C source and compiler output.

>> asm("move.l %2,%0;" /* 0x0001 */
>> "lsl.l #2,%0;" /* 0x0004 */
>> "move.l %0,%1;"
>> "lsl.l #7,%0;" /* 0x0200 */
>> "add.l %2,%0;" /* 0x0201 */
>> "add.l %0,%1;" /* 0x0205 */
>> "add.l %0,%0;" /* 0x0402 */
>> "add.l %0,%1;" /* 0x0607 */
>> "lsl.l #5,%0" /* 0x8040 */
>> /* 0x8647 */

> Also, it took me some time to understand the hexadecimal constants
> in the comments (and the last one predicts a future event :)).

Can you recmmend a better way to comment this? My nose is so deep
in the code it's hard for me to judge.

> Just my two cents

And thank you very much for them!