#endif
__morestack_non_split:
+ .cfi_startproc
#ifndef __x86_64__
- addl $0x4000,4(%esp)
+
+ # See below for an extended explanation of the CFI instructions.
+ .cfi_offset 8, 8 # New PC stored at CFA + 8
+ .cfi_escape 0x15, 4, 0x7d # DW_CFA_val_offset_sf, %esp, 12/-4
+ # i.e., next %esp is CFA + 12
+
+ pushl %eax # Save %eax in case it is a parameter.
+
+ .cfi_def_cfa %esp,8 # Account for pushed register.
+
+ movl %esp,%eax # Current stack,
+ subl 8(%esp),%eax # less required stack frame size,
+ subl $0x4000,%eax # less space for non-split code.
+ cmpl %gs:0x30,%eax # See if we have enough space.
+ jb 2f # Get more space if we need it.
+
+ # Here the stack is
+ # %esp + 20: stack pointer after two returns
+ # %esp + 16: return address of morestack caller's caller
+ # %esp + 12: size of parameters
+ # %esp + 8: new stack frame size
+ # %esp + 4: return address of this function
+ # %esp: saved %eax
+ #
+ # Since we aren't doing a full split stack, we don't need to
+ # do anything when our caller returns. So we return to our
+ # caller rather than calling it, and let it return as usual.
+ # To make that work we adjust the return address.
+
+ # This breaks call/return address prediction for the call to
+ # this function. I can't figure out a way to make it work
+ # short of copying the parameters down the stack, which will
+ # probably take more clock cycles than we will lose breaking
+ # call/return address prediction. We will only break
+ # prediction for this call, not for our caller.
+
+ movl 4(%esp),%eax # Increment the return address
+ cmpb $0xc3,(%eax) # to skip the ret instruction;
+ je 1f # see above.
+ addl $2,%eax
+1: inc %eax
+ movl %eax,4(%esp) # Update return address.
+
+ popl %eax # Restore %eax and stack.
+
+ .cfi_def_cfa %esp,4 # Account for popped register.
+
+ ret $8 # Return to caller, popping args.
+
+2:
+ .cfi_def_cfa %esp,8 # Back to where we were.
+
+ popl %eax # Restore %eax and stack.
+
+ .cfi_def_cfa %esp,4 # Account for popped register.
+
+ addl $0x5000+BACKOFF,4(%esp) # Increment space we request.
+
+ # Fall through into morestack.
+
#else
- addq $0x4000,%r10
+
+ # See below for an extended explanation of the CFI instructions.
+ .cfi_offset 16, 0
+ .cfi_escape 0x15, 7, 0x7f # DW_CFA_val_offset_sf, %esp, 8/-8
+
+ pushq %rax # Save %rax in case caller is using
+ # it to preserve original %r10.
+ .cfi_def_cfa %rsp,16 # Adjust for pushed register.
+
+ movq %rsp,%rax # Current stack,
+ subq %r10,%rax # less required stack frame size,
+ subq $0x4000,%rax # less space for non-split code.
+
+#ifdef __LP64__
+ cmpq %fs:0x70,%rax # See if we have enough space.
+#else
+ cmpl %fs:0x40,%eax
#endif
+ jb 2f # Get more space if we need it.
+
+ # This breaks call/return prediction, as described above.
+ incq 8(%rsp) # Increment the return address.
+
+ popq %rax # Restore register.
+
+ .cfi_def_cfa %rsp,8 # Adjust for popped register.
+ ret # Return to caller.
+
+2:
+ .cfi_def_cfa %rsp,16 # Back to where we were.
+
+ popq %rax # Restore register.
+
+ .cfi_def_cfa %rsp,8 # Adjust for popped register.
+
+ addq $0x5000+BACKOFF,%r10 # Increment space we request.
+
+ # Fall throug into morestack.
+
+#endif
+
+ .cfi_endproc
#ifdef __ELF__
.size __morestack_non_split, . - __morestack_non_split
#endif
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