rust morestack assembly for arm

Conflicts:
	src/rt/arch/arm/morestack.S

1 files changed, 54 insertions, 1 deletions

diff --git a/src/rt/arch/arm/morestack.S b/src/rt/arch/arm/morestack.S
index 1afce5bd848..3af8e898cdb 100644
--- a/src/rt/arch/arm/morestack.S
+++ b/src/rt/arch/arm/morestack.S
@@ -8,6 +8,59 @@
 .arm
 .align
 
-.globl __morestack
+.global upcall_new_stack
+.global upcall_del_stack
+.global __morestack
 .hidden __morestack
+
+// r4 and r5 are scratch registers for __morestack due to llvm
+// ARMFrameLowering::adjustForSegmentedStacks() implementation.
+    .align 2
+    .type __morestack,%function
 __morestack:
+
+    // Save frame pointer and return address
+    push {fp, lr}
+    
+    mov fp, sp
+
+    // Save argument registers of the original function
+    push {r0, r1, r2, r3, lr}
+
+    mov r0, r4         // The amount of stack needed
+    add r1, fp, #20    // Address of stack arguments
+    mov r2, r5         // Size of stack arguments
+    
+    // Create new stack
+    bl upcall_new_stack@plt
+
+    // Hold new stack pointer
+    mov r5, r0
+
+    // Pop the saved arguments
+    pop {r0, r1, r2, r3, lr}
+
+    // Grab the return pointer
+    add r4, lr, #16    // Skip past the return
+    mov sp, r5         // Swich to the new stack
+    mov lr, pc
+    mov pc, r4         // Call the original function
+
+    // Switch back to rust stack
+    mov sp, fp
+
+    // Save return value
+    push {r0, r1}
+
+    // Remove the new allocated stack
+    bl upcall_del_stack@plt
+
+    // Restore return value
+    pop {r0, r1}
+
+    // Return
+    pop {fp, lr}
+    mov pc, lr
+.endofmorestack:
+    .size   __morestack, .endofmorestack-__morestack
+