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#!/usr/bin/python
'''
/* This file generates libgcc_compat.c file that contains dummy
* references to libgcc.a functions to force the dynamic linker
* to copy their definition into the final libc.so binary.
*
* They are required to ensure backwards binary compatibility with
* libc.so provided by the platform and binaries built with the NDK or
* different versions/configurations of toolchains.
*
* Now, for a more elaborate description of the issue:
*
* libgcc.a is a compiler-specific library containing various helper
* functions used to implement certain operations that are not necessarily
* supported by the target CPU. For example, integer division doesn't have a
* corresponding CPU instruction on ARMv5, and is instead implemented in the
* compiler-generated machine code as a call to an __idiv helper function.
*
* Normally, one has to place libgcc.a in the link command used to generate
* target binaries (shared libraries and executables) after all objects and
* static libraries, but before dependent shared libraries, i.e. something
* like:
* gcc <options> -o libfoo.so foo.a libgcc.a -lc -lm
*
* This ensures that any helper function needed by the code in foo.a is copied
* into the final libfoo.so. However, doing so will link a bunch of other __cxa
* functions from libgcc.a into each .so and executable, causing 4k+ increase
* in every binary. Therefore the Android platform build system has been
* using this instead:
*
* gcc <options> -o libfoo.so foo.a -lc -lm libgcc.a
*
* The problem with this is that if one helper function needed by foo.a has
* already been copied into libc.so or libm.so, then nothing will be copied
* into libfoo.so. Instead, a symbol import definition will be added to it
* so libfoo.so can directly call the one in libc.so at runtime.
*
* When refreshing toolchains for new versions or using different architecture
* flags, the set of helper functions copied to libc.so may change, which
* resulted in some native shared libraries generated with the NDK or prebuilts
* from vendors to fail to load properly.
*
* The NDK has been fixed after 1.6_r1 to use the correct link command, so
* any native shared library generated with it should now be safe from that
* problem. On the other hand, existing shared libraries distributed with
* applications that were generated with a previous version of the NDK
* still need all 1.5/1.6 helper functions in libc.so and libm.so
*
* After 3.2, the toolchain was updated again, adding __aeabi_f2uiz to the
* list of requirements. Technically, this is due to mis-linked NDK libraries
* but it is easier to add a single function here than asking several app
* developers to fix their build.
*
* The __aeabi_idiv function is added to the list since cortex-a15 supports
* HW idiv instructions so the system libc.so doesn't pull in the reference to
* __aeabi_idiv but legacy libraries built against cortex-a9 targets still need
* it.
*
* Final note: some of the functions below should really be in libm.so to
* completely reflect the state of 1.5/1.6 system images. However,
* since libm.so depends on libc.so, it's easier to put all of
* these in libc.so instead, since the dynamic linker will always
* search in libc.so before libm.so for dependencies.
*/
'''
import os
import sys
import subprocess
import tempfile
import re
libgcc_compat_header = "/* Generated by genlibgcc_compat.py */\n\n"
class Generator:
def process(self):
android_build_top_path = os.environ["ANDROID_BUILD_TOP"]
print "* ANDROID_BUILD_TOP=" + android_build_top_path
# Check TARGET_ARCH
arch = subprocess.check_output(["CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core make --no-print-directory -f build/core/config.mk dumpvar-TARGET_ARCH"],
cwd=android_build_top_path, shell=True).strip()
if arch != 'arm' and arch != 'x86':
sys.exit("Error: Invalid TARGET_ARCH='" + arch + "' expecting 'arm' or 'x86'")
build_path = android_build_top_path + "/bionic/libc"
file_name = "libgcc_compat.c"
file_path = build_path + "/arch-" + arch + "/bionic/" + file_name
build_output_file_path = tempfile.mkstemp()[1]
p = subprocess.Popen(["ONE_SHOT_MAKEFILE=bionic/libc/Android.mk make -C " + android_build_top_path
+ " -f build/core/main.mk all_modules TARGET_LIBGCC= -j20 -B 2>&1 | tee " + build_output_file_path],
cwd=build_path, shell=True)
p.wait()
print "* Build complete, logfile: " + build_output_file_path
symbol_set = set()
prog=re.compile("(?<=undefined reference to ')\w+")
fd = open(build_output_file_path, 'r')
for line in fd:
m = prog.search(line)
if m:
symbol_set.add(m.group(0))
fd.close()
symbol_list = sorted(symbol_set)
print "* Found " + repr(len(symbol_list)) + " referenced symbols: " + repr(symbol_list)
if 0 == len(symbol_list):
sys.exit("Error: symbol list is empty, please check the build log: " + build_output_file_path)
print "* Generating " + file_path
fres = open(file_path, 'w')
fres.write(libgcc_compat_header)
for sym_name in symbol_list:
fres.write("extern char "+sym_name+";\n")
fres.write("\n");
fres.write("void* __bionic_libgcc_compat_symbols[] = {\n");
for sym_name in symbol_list:
fres.write(" &"+sym_name+",\n")
fres.write("};\n");
fres.close()
generator = Generator()
generator.process()
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