Messages in this thread | | | From | Linus Torvalds <> | Date | Sun, 14 Nov 2010 19:21:50 -0800 | Subject | Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ? |
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On Sun, Nov 14, 2010 at 4:52 PM, James Cloos <cloos@jhcloos.com> wrote: > Gcc 4.5.1 running on an amd64 box "cross"-compiling for a P3 i8k fails > to compile the module since commit 6b4e81db2552bad04100e7d5ddeed7e848f53b48 > with: > > CC drivers/char/i8k.o > drivers/char/i8k.c: In function ‘i8k_smm’: > drivers/char/i8k.c:149:2: error: can't find a register in class ‘GENERAL_REGS’ while reloading ‘asm’ > drivers/char/i8k.c:149:2: error: ‘asm’ operand has impossible constraints
At this point, I think this falls clearly under "unresolvable gcc bug".
Quite frankly, I think gcc was buggy to begin with: since we had a memory clobber, the "+m" (*regs) should not have mattered. The fact that "*regs" may be some local variable doesn't make any difference what-so-ever, since we took the address of the variable. So the memory clobber _clearly_ can change that variable.
So when Richard Gunther says "a memory clobber doesn't cover automatic storage", to me that very clearly spells "gcc is buggy as hell". Because automatic storage with its address taken _very_ much gets clobbered by things like memset etc. If the compiler doesn't understand that, the compiler is just broken.
And now, if even the (superfluous) "+m" isn't working, it sounds like we have no sane options left. Except to say that gcc-4.5.1 is totally broken wrt asms.
Can we just get gcc to realize that when you pass the address of automatic storage to an asm, that means that "memory" really does clobber it? Because clearly that is the case.
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