On Sun, Aug 16, 2015 at 06:33:40PM -0700, David Wohlferd wrote: > As a followup to my update to the inline asm docs, I'm cleaning up the > docs for 'Asm Labels.' The changes I want to make are pretty > straight-forward (attached; comments welcome). But then I came across > this line of code (from > https://github.com/rschmukler/cs537-p5/blob/master/xv6/proc.h#L38): > > extern struct proc *proc asm("%gs:4"); > > This x86 code says that 'proc' is located at an offset of 4 bytes from > the gs register.
It says that the assembler name of the function is "%gs:4"; it works by accident, not by design (imagine what would happen if the function was defined in this same translation unit!) > There isn't any description of using asm like this in the current Asm > Labels docs. And there shouldn't be. It's a hack. Segher
