all: add linux/mipsle support

This adds linux/mipsle (little endian Mips) support to TinyGo.

It also adds experimental linux/mips (big-endian) support. It doesn't
quite work yet, some parts of the standard library (like the reflect
package) currently seem to assume a little-endian system.

src/runtime/arch_386.go

@@ -9,6 +9,8 @@ const deferExtraRegs = 0
 
 const callInstSize = 5 // "call someFunction" is 5 bytes
 
+const linux_MAP_ANONYMOUS = 0x20
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 15) &^ 15

src/runtime/arch_amd64.go

@@ -9,6 +9,8 @@ const deferExtraRegs = 0
 
 const callInstSize = 5 // "call someFunction" is 5 bytes
 
+const linux_MAP_ANONYMOUS = 0x20
+
 // Align a pointer.
 // Note that some amd64 instructions (like movaps) expect 16-byte aligned
 // memory, thus the result must be 16-byte aligned.

src/runtime/arch_arm.go

@@ -11,6 +11,8 @@ const deferExtraRegs = 0
 
 const callInstSize = 4 // "bl someFunction" is 4 bytes
 
+const linux_MAP_ANONYMOUS = 0x20
+
 // Align on the maximum alignment for this platform (double).
 func align(ptr uintptr) uintptr {
 	return (ptr + 7) &^ 7

src/runtime/arch_arm64.go

@@ -9,6 +9,8 @@ const deferExtraRegs = 0
 
 const callInstSize = 4 // "bl someFunction" is 4 bytes
 
+const linux_MAP_ANONYMOUS = 0x20
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 15) &^ 15

src/runtime/arch_mips.go

@@ -0,0 +1,21 @@
+package runtime
+
+const GOARCH = "mips"
+
+// The bitness of the CPU (e.g. 8, 32, 64).
+const TargetBits = 32
+
+const deferExtraRegs = 0
+
+const callInstSize = 8 // "jal someFunc" is 4 bytes, plus a MIPS delay slot
+
+const linux_MAP_ANONYMOUS = 0x800
+
+// It appears that MIPS has a maximum alignment of 8 bytes.
+func align(ptr uintptr) uintptr {
+	return (ptr + 7) &^ 7
+}
+
+func getCurrentStackPointer() uintptr {
+	return uintptr(stacksave())
+}

src/runtime/arch_mipsle.go

@@ -0,0 +1,21 @@
+package runtime
+
+const GOARCH = "mipsle"
+
+// The bitness of the CPU (e.g. 8, 32, 64).
+const TargetBits = 32
+
+const deferExtraRegs = 0
+
+const callInstSize = 8 // "jal someFunc" is 4 bytes, plus a MIPS delay slot
+
+const linux_MAP_ANONYMOUS = 0x800
+
+// It appears that MIPS has a maximum alignment of 8 bytes.
+func align(ptr uintptr) uintptr {
+	return (ptr + 7) &^ 7
+}
+
+func getCurrentStackPointer() uintptr {
+	return uintptr(stacksave())
+}

src/runtime/asm_mipsx.S

@@ -0,0 +1,40 @@
+.section .text.tinygo_scanCurrentStack
+.global  tinygo_scanCurrentStack
+.type    tinygo_scanCurrentStack, %function
+tinygo_scanCurrentStack:
+    // Push callee-saved registers onto the stack.
+    addiu $sp, $sp, -40
+    sw $ra, 36($sp)
+    sw $s8, 32($sp)
+    sw $s7, 28($sp)
+    sw $s6, 24($sp)
+    sw $s5, 20($sp)
+    sw $s4, 16($sp)
+    sw $s3, 12($sp)
+    sw $s2,  8($sp)
+    sw $s1,  4($sp)
+    sw $s0,   ($sp)
+
+    // Scan the stack.
+    jal tinygo_scanstack
+    move $a0, $sp // in the branch delay slot
+
+    // Restore return address.
+    lw $ra, 36($sp)
+
+    // Restore stack state.
+    addiu $sp, $sp, 40
+
+    // Return to the caller.
+    jalr $ra
+    nop
+
+.section .text.tinygo_longjmp
+.global tinygo_longjmp
+tinygo_longjmp:
+    // Note: the code we jump to assumes a0 is non-zero, which is already the
+    // case because that's the defer frame pointer.
+    lw $sp, 0($a0) // jumpSP
+    lw $a1, 4($a0) // jumpPC
+    jr $a1
+    nop

src/runtime/os_linux.go

@@ -14,7 +14,7 @@ const (
 	flag_PROT_READ     = 0x1
 	flag_PROT_WRITE    = 0x2
 	flag_MAP_PRIVATE   = 0x2
-	flag_MAP_ANONYMOUS = 0x20
+	flag_MAP_ANONYMOUS = linux_MAP_ANONYMOUS // different on alpha, hppa, mips, xtensa
 )
 
 // Source: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time.h

src/runtime/runtime_unix.go

@@ -229,6 +229,9 @@ func preinit() {
 			// heap size.
 			// This can happen on 32-bit systems.
 			heapMaxSize /= 2
+			if heapMaxSize < 4096 {
+				runtimePanic("cannot allocate heap memory")
+			}
 			continue
 		}
 		heapStart = uintptr(addr)