we can be interrupted, and deliverable interrupts
automatically prioritize over us.
+ The start of the stack (before the VMM pushes the fake
+ interrupt frame is 16 byte aligned
+
48bitsblank | return SS (16 bits)
Return RSP
Return RFLAGS
We then need simply to do this:
save regs
+ arrange 16 byte alignment at entry of call
call the handler (if installed)
restore regs
iret
*/
+#define DEBUG_ENTRY 0
+
.global __v3_hvm_ros_signal_handler_stub
-__v3_hvm_ros_signal_handler_stub:
- GPR_SAVE()
- movabs __v3_hvm_ros_signal_handler, %rax
- testq %rax, %rax
- jz skip_handler
- movq 120(%rsp), %rdi /* error code becomes argument */
- callq *%rax
-skip_handler:
- GPR_LOAD()
- addq $8, %rsp /* nuke the error code */
- iretq
+__v3_hvm_ros_signal_handler_stub: /* we are 16 byte aligned on entry 16 + 6*8 for interrupt frame */
+ GPR_SAVE() /* push 15 words, all but rsp, now not aligned - need 1 more word */
+ subq $8, %rsp /* make us 16 byte aligned */
+
+#if DEBUG_ENTRY /* print out something if we are debugging - Note this is danerous code */
+ pushq %rdi
+ pushq %rax
+ movabsq $printf, %rax
+ movabsq $string, %rdi
+ callq *%rax
+ popq %rax
+ popq %rdi
+#endif
+ movq %rsp, %rbp /* give us a stack frame for any callee that needs it */
+ movabs __v3_hvm_ros_signal_handler, %rax /* find the user-level handler */
+ testq %rax, %rax /* return immediately if it doesn't exist */
+ jz skip_handler /* " */
+ movq 128(%rsp), %rdi /* error code becomes argument for user-level handler */
+ callq *%rax /* call handelr - 16 byte aligned at call */
+ jmp done
+skip_handler:
+done:
+ addq $8, %rsp /* get rid of stack alignment pad */
+ GPR_LOAD() /* rbp is restored here */
+ addq $8, %rsp /* nuke the error code */
+ iretq /* restore rip, rsp, and rflags */
+
+string:
+ .asciz "Got to signal handler stub\12"
