Allow use of ^blocks, even with the 10.5 SDK, and even with a 10.5 runtime

chrome/browser/mac/closure_blocks_leopard_compat.S

+# Copyright (c) 2011 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Definitions of symbols that may be needed at runtime but aren't necessarily
+# present in the SDK chosen for compilation.
+#
+# This file provides a symbols for _NSConcreteGlobalBlock and
+# _NSConcreteStackBlock, normally present in libSystem.dylib and provided by
+# by libclosure-38/data.c in Mac OS X 10.6 and later. When using the 10.5 SDK,
+# the symbol is not present. This file's definition can be used with extreme
+# care in an application that needs to use the 10.5 SDK in conjunction with
+# blocks.
+#
+# This file cooperates with the build system (closure_leopard_compat.gyp) to
+# produce a dynamic library that, when linked against, causes dependents to
+# look in libSystem for the symbols provided here. It also cooperates with a
+# header (block.h) that causes dependents to treat the symbols provided here
+# as weak imports, critical for the resultant output to be loadable on 10.5.
+
+# To simplify things, this file assumes it's being built with the 10.5 SDK,
+# a deployment target of 10.5, and is producing 32-bit x86 code. Other
+# combinations are possible, but not interesting for the time being. See
+# <sys/cdefs.h> for interesting ways that names might be mangled in other
+# configurations.
+
+#include <AvailabilityMacros.h>

[Nico, 2011/08/08 21:03:40]

Just out of curiosity, why a .S file instead of a "normal" c file?

+
+#if MAC_OS_X_VERSION_MIN_REQUIRED != MAC_OS_X_VERSION_10_5 || \
+    MAC_OS_X_VERSION_MAX_ALLOWED != MAC_OS_X_VERSION_10_5 || \
+    !defined(__i386__)
+#error This file only supports 32-bit x86 code with both SDK and DT set to 10.5
+#endif
+
+#define DEFINE_GLOBAL_SYMBOL(name) \
+    .globl name ## ;\
+    name ## :
+
+.section __DATA,__data
+
+DEFINE_GLOBAL_SYMBOL(__NSConcreteGlobalBlock)
+DEFINE_GLOBAL_SYMBOL(__NSConcreteStackBlock)
+
+# When this file is in use, the linker is expected to link things against both
+# this file and the real copy of libSystem present in the SDK. When doing so,
+# the linker is smart enough to produce only one LC_LOAD_DYLIB load command.
+# However, it's not smart enough to notice that while this file's dylib only
+# provides weak-imported symbols, the real libSystem's dylib does not.
+# Consequently, it may produce an LC_LOAD_WEAK_DYLIB load command for
+# libSystem instead of an ordinary LC_LOAD_DYLIB command. LC_LOAD_WEAK_DYLIB
+# declares that any symbol offered by the library, and in fact the entire
+# library, is permitted to be missing at runtime. This is entirely
+# inappropriate for libSystem. To counteract this problem, this file also
+# defines some other symbols that libSystem provides. Dependents of this
+# library are not expected to treat these other symbols as weak imports. In
+# order for any dependent that links against this library to load it with an
+# LC_LOAD_DYLIB command instead of an LC_LOAD_WEAK_DYLIB command, this library
+# must satisfy at least one unresolved non-weak-import symbol required by the
+# dependent.
+
+.text
+
+# |exit| is a good one: because it's referenced by crt1.o, ordinary executables
+# are guaranteed to need this symbol. Unfortunately, there's no such symbol in
+# dylib1.o that libSystem is expected to provide, so a few other common libc
+# symbols are thrown into the mix.
+DEFINE_GLOBAL_SYMBOL(_exit)
+
+# Include |close| because well-written programs that use the standard library
+# are likely to refer to it. Include |open| for good measure because it goes
+# pretty well with this. Include the stdio abstractions for these functions
+# as well.
+DEFINE_GLOBAL_SYMBOL(_close$UNIX2003)
+DEFINE_GLOBAL_SYMBOL(_open$UNIX2003)
+DEFINE_GLOBAL_SYMBOL(_fclose)
+DEFINE_GLOBAL_SYMBOL(_fopen)
+DEFINE_GLOBAL_SYMBOL(_fdopen)
+DEFINE_GLOBAL_SYMBOL(_freopen$UNIX2003)
+
+# Commonly-used allocation functions.
+DEFINE_GLOBAL_SYMBOL(_malloc)
+DEFINE_GLOBAL_SYMBOL(_calloc)
+DEFINE_GLOBAL_SYMBOL(_realloc)
+DEFINE_GLOBAL_SYMBOL(_reallocf)
+DEFINE_GLOBAL_SYMBOL(_valloc)
+DEFINE_GLOBAL_SYMBOL(_free)
+
+# Include |printf|, |fprintf|, |sprintf|, |snprintf|, and |puts|, because
+# small test programs are likely to refer to one of these. puts is rarely
+# invoked directly, but the compiler may optimize simple printf calls into
+# puts calls.
+DEFINE_GLOBAL_SYMBOL(_printf)
+DEFINE_GLOBAL_SYMBOL(_fprintf)
+DEFINE_GLOBAL_SYMBOL(_sprintf)
+DEFINE_GLOBAL_SYMBOL(_snprintf)
+DEFINE_GLOBAL_SYMBOL(_puts)
+
+# Some <string.h> functions that are commonly used.
+DEFINE_GLOBAL_SYMBOL(_memcmp)
+DEFINE_GLOBAL_SYMBOL(_memcpy)
+DEFINE_GLOBAL_SYMBOL(_memmove)
+DEFINE_GLOBAL_SYMBOL(_memset)
+DEFINE_GLOBAL_SYMBOL(_strcasecmp)
+DEFINE_GLOBAL_SYMBOL(_strcat)
+DEFINE_GLOBAL_SYMBOL(_strchr)
+DEFINE_GLOBAL_SYMBOL(_strcmp)
+DEFINE_GLOBAL_SYMBOL(_strcpy)
+DEFINE_GLOBAL_SYMBOL(_strdup)
+DEFINE_GLOBAL_SYMBOL(_strlcat)
+DEFINE_GLOBAL_SYMBOL(_strlcpy)
+DEFINE_GLOBAL_SYMBOL(_strlen)
+DEFINE_GLOBAL_SYMBOL(_strncasecmp)
+DEFINE_GLOBAL_SYMBOL(_strncat)
+DEFINE_GLOBAL_SYMBOL(_strncmp)
+DEFINE_GLOBAL_SYMBOL(_strncpy)
+DEFINE_GLOBAL_SYMBOL(_strnstr)
+DEFINE_GLOBAL_SYMBOL(_strstr)
+
+# Some data-section symbols that might be referenced.
+
+.section __DATA,__data
+
+DEFINE_GLOBAL_SYMBOL(___stdinp)
+DEFINE_GLOBAL_SYMBOL(___stdoutp)
+DEFINE_GLOBAL_SYMBOL(___stderrp)
+
+#undef DEFINE_GLOBAL_SYMBOL