Hi! On Tue, Feb 16, 2021 at 08:36:02PM +1100, Michael Ellerman wrote: > Feng Tang <feng.tang(a)intel.com&gt; writes: > > {standard input}:577: Error: unsupported relocation against base > > {standard input}:580: Error: unsupported relocation against base > > {standard input}:583: Error: unsupported relocation against base > > The reason is macro 'mfdcr' requirs an instant number as parameter, > > which is not met by show_plbopb_regs(). > > It doesn't require a constant, it checks if the argument is constant: > > #define mfdcr(rn) \ > ({unsigned int rval; \ > if (__builtin_constant_p(rn) && rn < 1024) \ > asm volatile("mfdcr %0," __stringify(rn) \ > : "=r" (rval)); \ > else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR))) \ > rval = mfdcrx(rn); \ > else \ > rval = __mfdcr(rn); \ > rval;}) It requires a constant number with known (at compile time) value, while __builtin_constant_p checks for any constant. The address of some defined symbol is a constant as well normally, for example. It's better to write that asm as asm volatile("mfdcr %0,%1" : "=r" (rval) : "n"(rn)); btw (the "n" constraint means "constant integer with known value" (it stands for "numeric"), while the "i" constraint means just "constant integer").