ios - 无法在支持 SIMD/NEON 的 Xcode 5/Clang 工具链上为 iOS 编译 libjpeg-turbo

Question

看起来像 Xcode 5 和 LLVM-GCC-4.2 的删除及其由 Clang 的替代，在 NEON 支持的编译过程中，为 iOS 设备构建 libjpeg-turbo 现在失败了。

配置步骤:

export PLATFORM="iPhoneOS"
export IPHONE_SDK="7.0"
export IPHONE_MIN_VERSION="5.0"

export DEVELOPER=`xcode-select --print-path`
export DEVROOT="${DEVELOPER}/Platforms/${PLATFORM}.platform/Developer"
export SDKROOT="${DEVROOT}/SDKs/${PLATFORM}${IPHONE_SDK}.sdk"
export CC=`xcrun -find gcc`
export LD=`xcrun -find ld`
export IOS_CFLAGS="-arch armv7"
export CFLAGS="-O3 ${IOS_CFLAGS} -isysroot ${SDKROOT}"
export LDFLAGS="${IOS_CFLAGS} -isysroot ${SDKROOT}"
export CPPFLAGS="${CFLAGS}"
export CFLAGS="${CFLAGS} -miphoneos-version-min=${IPHONE_MIN_VERSION}"

./configure --with-jpeg8 --host arm-apple-darwin --enable-static --disable-shared
...
checking if we have SIMD optimisations for cpu type... yes (arm)
checking if the assembler is GNU-compatible and can be used... yes
...

构建步骤:

make -j4
    /Applications/Xcode.app/Contents/Developer/usr/bin/make  all-recursive
Making all in java
echo timestamp > classnodist_noinst.stamp
Making all in simd
/Applications/Xcode.app/Contents/Developer/usr/bin/gcc -E -I.. -I../simd ./jsimdcfg.inc.h | grep -E "^[\;%]|^\ %" | sed 's%_cpp_protection_%%' | sed 's@% define@%define@g' > jsimdcfg.inc
/Applications/Xcode.app/Contents/Developer/usr/bin/make  all-am
if /bin/sh ../libtool --mode=compile --tag=CC /Applications/Xcode.app/Contents/Developer/usr/bin/gcc -DHAVE_CONFIG_H -I. -I. -I.. -I..  -I..  -O3 -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk  -O3 -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk -miphoneos-version-min=5.0 -MT jsimd_arm.lo -MD -MP -MF ".deps/jsimd_arm.Tpo" -c -o jsimd_arm.lo jsimd_arm.c; \
    then mv -f ".deps/jsimd_arm.Tpo" ".deps/jsimd_arm.Plo"; else rm -f ".deps/jsimd_arm.Tpo"; exit 1; fi
/bin/sh ../libtool --mode=compile gas-preprocessor.pl /Applications/Xcode.app/Contents/Developer/usr/bin/gcc  -O3 -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk -miphoneos-version-min=5.0 -c -o jsimd_arm_neon.lo jsimd_arm_neon.S
libtool: compile: unable to infer tagged configuration
libtool: compile: specify a tag with `--tag'
make[3]: *** [jsimd_arm_neon.lo] Error 1
make[3]: *** Waiting for unfinished jobs....
 /Applications/Xcode.app/Contents/Developer/usr/bin/gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I.. -O3 -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk -O3 -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk -miphoneos-version-min=5.0 -MT jsimd_arm.lo -MD -MP -MF .deps/jsimd_arm.Tpo -c jsimd_arm.c -o jsimd_arm.o
make[2]: *** [all] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

知道如何解决这个问题吗？如果禁用 SIMD 支持，构建会成功，但这显然不是很好。

Answer 1

它已被 libjpeg-turbo 的维护者修复: http://sourceforge.net/mailarchive/message.php?msg_id=31902025

需要的是一个特殊的 CLANG 兼容版本的气体预处理器: http://sourceforge.net/p/libjpeg-turbo/code/HEAD/tree/gas-preprocessor/