[builtins] Implement the __chkstk function for ARM for MinGW

This function is available for linking in from kernel32.dll, but
it's not allowed to link that function from there in Windows Store
apps.

Differential Revision: https://reviews.llvm.org/D49055

llvm-svn: 337313

compiler-rt/lib/builtins/CMakeLists.txt

@@ -406,6 +406,7 @@ if(MINGW)
       arm/aeabi_ldivmod.S
       arm/aeabi_uidivmod.S
       arm/aeabi_uldivmod.S
+      arm/chkstk.S
       divmoddi4.c
       divmodsi4.c
       divdi3.c

compiler-rt/lib/builtins/arm/chkstk.S

@@ -0,0 +1,34 @@
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+
+#include "../assembly.h"
+
+// __chkstk routine
+// This routine is windows specific.
+// http://msdn.microsoft.com/en-us/library/ms648426.aspx
+
+// This clobbers the register r12, and the condition codes, and uses r5 and r6
+// as temporaries by backing them up and restoring them afterwards.
+// Does not modify any memory or the stack pointer.
+
+//      movw    r4,  #256 // Number of bytes of stack, in units of 4 byte
+//      bl      __chkstk
+//      sub.w   sp, sp, r4
+
+#define PAGE_SIZE 4096
+
+        .p2align 2
+DEFINE_COMPILERRT_FUNCTION(__chkstk)
+        lsl    r4,  r4,  #2
+        mov    r12, sp
+        push   {r5, r6}
+        mov    r5,  r4
+1:
+        sub    r12, r12, #PAGE_SIZE
+        subs   r5,  r5,  #PAGE_SIZE
+        ldr    r6,  [r12]
+        bgt    1b
+
+        pop    {r5, r6}
+        bx     lr
+END_COMPILERRT_FUNCTION(__chkstk)