diff options
Diffstat (limited to 'sys/arch/mvme88k/m88k/syscall.stub')
| -rw-r--r-- | sys/arch/mvme88k/m88k/syscall.stub | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/sys/arch/mvme88k/m88k/syscall.stub b/sys/arch/mvme88k/m88k/syscall.stub new file mode 100644 index 00000000000..4a1055556d1 --- /dev/null +++ b/sys/arch/mvme88k/m88k/syscall.stub @@ -0,0 +1,29 @@ + /* + * system call will look like: + * ld r10, r31, 32; r10,r11,r12 might be garbage. + * ld r11, r31, 36 + * ld r12, r31, 40 + * or r13, r0, <code> + * tb0 0, r0, <128> <- xip + * br err <- nip + * jmp r1 <- fip + * err: or.u r3, r0, hi16(errno) + * st r2, r3, lo16(errno) + * subu r2, r0, 1 + * jmp r1 + * + * So, when we take syscall trap, sxip/snip/sfip will be as + * shown above. + * Given this, + * 1. If the system call returned 0, need to skip nip. + * nip = fip, fip += 4 + * (doesn't matter what fip + 4 will be but we will never + * execute this since jmp r1 at nip will change the execution flow.) + * 2. If the system call returned an errno > 0, plug the value + * in r2, and leave nip and fip unchanged. This will have us + * executing "br err" on return to user space. + * 3. If the system call code returned ERESTART or EJUSTRETURN, + * we need to rexecute the trap instruction. Back up the pipe + * line. + * fip = nip, nip = xip + */ |