ARM: Clean up FlushICache.

src/arm/cpu-arm.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // CPU specific code for arm independent of OS goes here.
 #ifdef __arm__
 #ifdef __QNXNTO__
 #include <sys/mman.h>  // for cache flushing.
 #undef MAP_TYPE
 #else
 #include <sys/syscall.h>  // for cache flushing.
 #endif
 #endif
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/cpu.h"
 #include "src/macro-assembler.h"
 #include "src/simulator.h"  // for cache flushing.
 
 namespace v8 {
 namespace internal {
 
+#if defined(USE_SIMULATOR)
+
 void CPU::FlushICache(void* start, size_t size) {
-  // Nothing to do flushing no instructions.
-  if (size == 0) {
-    return;
-  }
-
-#if defined(USE_SIMULATOR)
+  if (size == 0) return;
   // Not generating ARM instructions for C-code. This means that we are
   // building an ARM emulator based target.  We should notify the simulator
   // that the Icache was flushed.
   // None of this code ends up in the snapshot so there are no issues
   // around whether or not to generate the code when building snapshots.
   Simulator::FlushICache(Isolate::Current()->simulator_i_cache(), start, size);
+}
+
 #elif V8_OS_QNX
-  msync(start, size, MS_SYNC | MS_INVALIDATE_ICACHE);
+
+void CPU::FlushICache(void* start, size_t size) {
+  if (size > 0) msync(start, size, MS_SYNC | MS_INVALIDATE_ICACHE);
+}
+
 #else
-  // Ideally, we would call
-  //   syscall(__ARM_NR_cacheflush, start,
-  //           reinterpret_cast<intptr_t>(start) + size, 0);
-  // however, syscall(int, ...) is not supported on all platforms, especially
-  // not when using EABI, so we call the __ARM_NR_cacheflush syscall directly.
 
-  register uint32_t beg asm("a1") = reinterpret_cast<uint32_t>(start);
-  register uint32_t end asm("a2") =
-      reinterpret_cast<uint32_t>(start) + size;
-  register uint32_t flg asm("a3") = 0;
-  #if defined (__arm__) && !defined(__thumb__)
-    // __arm__ may be defined in thumb mode.
-    register uint32_t scno asm("r7") = __ARM_NR_cacheflush;
-    asm volatile(
-        "svc 0x0"
-        : "=r" (beg)
-        : "0" (beg), "r" (end), "r" (flg), "r" (scno));
-  #else
-    // r7 is reserved by the EABI in thumb mode.
-    asm volatile(
-    "@   Enter ARM Mode  \n\t"
-        "adr r3, 1f      \n\t"
-        "bx  r3          \n\t"
-        ".ALIGN 4        \n\t"
-        ".ARM            \n"
-    "1:  push {r7}       \n\t"
-        "mov r7, %4      \n\t"
-        "svc 0x0         \n\t"
-        "pop {r7}        \n\t"
-    "@   Enter THUMB Mode\n\t"
-        "adr r3, 2f+1    \n\t"
-        "bx  r3          \n\t"
-        ".THUMB          \n"
-    "2:                  \n\t"
-        : "=r" (beg)
-        : "0" (beg), "r" (end), "r" (flg), "r" (__ARM_NR_cacheflush)
-        : "r3");
-  #endif
+void __attribute__((naked)) CPU::FlushICache(void* start, size_t size) {

[ulan, 2014/06/18 14:08:31]

Do you know if this attribute is supported by clang? I can't find any reference.

[jbramley, 2014/06/18 14:19:37]

I couldn't find a definite source, but the following pages strongly hint that
Clang supports it:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52646
http://comments.gmane.org/gmane.comp.compilers.clang.devel/29171

I also couldn't find reference to it (or any other __attribute__) in Clang's
manual, but it's _not_ included in the list of GCC features that aren't yet
supported:
http://clang.llvm.org/docs/UsersManual.html#gcc-extensions-not-implemented-yet

I was hoping that the try servers would have a Clang builder, but they don't. (I
don't have a Clang tool chain set up here.)

+  // On entry:
+  //  r0 = start
+  //  r1 = size
+  asm volatile(
+    // This assembly works for both ARM and Thumb targets.
+
+    // Preserve r7, since it is callee-saved.
+    "  push {r7, lr}\n"
+
+    // Perform the syscall (if size > 0).
+    "  cmp r1, #0\n"
+    "  beq 0f\n"
+                                  // r0 = start
+    "  adds r1, r1, r0\n"         // r1 = end (= start + size)
+    "  movs r2, #0\n"             // r2 = flags (= 0)
+    "  ldr r7, =%[scno]\n"        // r7 = syscall number.
+    "  svc 0\n"
+
+    // Restore r7 and return.
+    "0:\n"
+    "  pop {r7, pc}\n"
+    : : [scno] "i" (__ARM_NR_cacheflush) : "memory", "cc");
+}
+
 #endif
-}
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM