Make some small Mac-specific modifications to V8 to make it work on MacOS X 10.4

rather than just 10.5 and up.
1: Set the right compile flags and predefines to get backward compatible Unix
system calls.
2: Explicitly weak import the functions in execinfo.h and check at runtime to
see if that library loaded before calling backtrace(). 

Original change submitted by maf@google.com and reviewed at http://codereview.chromium.org/126241.
Review URL: http://codereview.chromium.org/132002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2213 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

SConstruct

@@ -125,7 +125,7 @@ LIBRARY_FLAGS = {
       }
     },
     'os:macos': {
-      'CCFLAGS':      ['-ansi'],
+      'CCFLAGS':      ['-ansi', '-mmacosx-version-min=10.4'],
     },
     'os:freebsd': {
       'CPPPATH' : ['/usr/local/include'],
@@ -641,7 +641,7 @@ def GetVersionComponents():
 
 def GetVersion():
   version_components = GetVersionComponents()
-  
+
   if version_components[len(version_components) - 1] == '0':
     version_components.pop()
   return '.'.join(version_components)
@@ -649,10 +649,10 @@ def GetVersion():
 
 def GetSpecificSONAME():
   SONAME_PATTERN = re.compile(r"#define\s+SONAME\s+\"(.*)\"")
-  
+
   source = open(join(root_dir, 'src', 'version.cc')).read()
   match = SONAME_PATTERN.search(source)
-  
+
   if match:
     return match.group(1).strip()
   else:

src/platform-macos.cc

@@ -35,10 +35,6 @@
 
 #include <AvailabilityMacros.h>
 
-#ifdef MAC_OS_X_VERSION_10_5
-# include <execinfo.h>  // backtrace, backtrace_symbols
-#endif
-
 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
@@ -58,6 +54,17 @@
 
 #include "platform.h"
 
+// Manually define these here as weak imports, rather than including execinfo.h.
+// This lets us launch on 10.4 which does not have these calls.
+extern "C" {
+  extern int backtrace(void**, int) __attribute__((weak_import));
+  extern char** backtrace_symbols(void* const*, int)
+      __attribute__((weak_import));
+  extern void backtrace_symbols_fd(void* const*, int, int)
+      __attribute__((weak_import));
+}
+
+
 namespace v8 {
 namespace internal {
 
@@ -214,9 +221,10 @@ int OS::ActivationFrameAlignment() {
 
 
 int OS::StackWalk(Vector<StackFrame> frames) {
-#ifndef MAC_OS_X_VERSION_10_5
-  return 0;
-#else
+  // If weak link to execinfo lib has failed, ie because we are on 10.4, abort.
+  if (backtrace == NULL)
+    return 0;
+
   int frames_size = frames.length();
   void** addresses = NewArray<void*>(frames_size);
   int frames_count = backtrace(addresses, frames_size);
@@ -244,7 +252,6 @@ int OS::StackWalk(Vector<StackFrame> frames) {
   free(symbols);
 
   return frames_count;
-#endif
 }