On Thu, Oct 15, 2015 at 09:59:03AM +0200, Hadrien Grasland wrote: > I am trying to write inline assembly code that uses the x86 floating > point stack. > > As far as I understood > https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Clobbers , the > proper register clobber to use in this case is "st(x)". For example, > this example from the documentation uses the "st(1)" clobber : > > asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); > > However, if I try it on the trivial example attached, it fails with the > following error. > > $ gcc-4.8 display_representation.c > display_representation.c: In function ‘main’: > display_representation.c:11:5: error: unknown register name ‘st(0)’ in ‘asm’ > asm volatile ("fstps (%1)" : > ^ > > What am I doing wrong ? I'm not sure you can clobber stack regs at all. You could add it as an output and just not use the result? Like asm ("fyl2xp1" : "=t" (result), "=u" (dummy) : "0" (x), "1" (y)); Segher
