function::register.3stap man page
function::register — Return the signed value of the named CPU register
Name of the register to return
Return the value of the named CPU register, as it was saved when the current probe point was hit. If the register is 32 bits, it is sign-extended to 64 bits.
For the i386 architecture, the following names are recognized. (name1/name2 indicates that name1 and name2 are alternative names for the same register.) eax/ax, ebp/bp, ebx/bx, ecx/cx, edi/di, edx/dx, eflags/flags, eip/ip, esi/si, esp/sp, orig_eax/orig_ax, xcs/cs, xds/ds, xes/es, xfs/fs, xss/ss.
For the x86_64 architecture, the following names are recognized: 64-bit registers: r8, r9, r10, r11, r12, r13, r14, r15, rax/ax, rbp/bp, rbx/bx, rcx/cx, rdi/di, rdx/dx, rip/ip, rsi/si, rsp/sp; 32-bit registers: eax, ebp, ebx, ecx, edx, edi, edx, eip, esi, esp, flags/eflags, orig_eax; segment registers: xcs/cs, xss/ss.
For powerpc, the following names are recognized: r0, r1, ... r31, nip, msr, orig_gpr3, ctr, link, xer, ccr, softe, trap, dar, dsisr, result.
For s390x, the following names are recognized: r0, r1, ... r15, args, psw.mask, psw.addr, orig_gpr2, ilc, trap.
For AArch64, the following names are recognized: x0, x1, ... x30, fp, lr, sp, pc, and orig_x0.