Tuesday, May 10, 2011

ffmpeg configure error on iPhone SDK.

 On building ffmpeg project targetting for iPhone OS, you may encounter configure error. The reason is that GCC in XCode 4.0 and 3.2.6 do not recognize the "sysroot" command line option. See following article for more information on configure error.

GCC changes in XCode 4.0 and 3.2.6

From XCode 4.0 GM and XCode 3.2.6, I found some my configure scripts for iOS aborted with the following errors.

$ export CFLAGS=-std=c99 -arch armv6 --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
-isystem /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk/usr/include
$ export LDFLAGS=-arch armv6 --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
$ ./configure --host="arm-apple-darwin"
configure: WARNING: If you wanted to set the --build type, don't use --host.
If a cross compiler is detected then cross compile mode will be used.
checking build system type... i386-apple-darwin10.6.0
checking host system type... arm-apple-darwin
checking for arm-apple-darwin-gcc... /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc
checking for C compiler default output... configure: error: C compiler cannot create executables

According to the config.log, the configure script couldn't build the executable file because the linker couldn't found libcache for armv6.

$ less config.log
configure:xxxx: /Developer326/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc -std=c99 -arch armv6
-isystem /Developer326/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk/usr/include
conftest.c >&5
ld: file not found: /usr/lib/system/libcache.dylib for architecture armv6
collect2: ld returned 1 exit status
configure:xxxx: $? = 1
configure:xxxx: result:
configure: failed program was:
| /* confdefs.h. */
| #define PACKAGE_NAME ""
| #define PACKAGE_TARNAME ""
| #define PACKAGE_VERSION ""
| #define PACKAGE_STRING ""
| /* end confdefs.h. */
| int
| main ()
| {
| ;
| return 0;
| }
configure:xxxx: error: in `xxxx:
configure:xxxx: error: C compiler cannot create executables

I created a new sample library project using XCode 4.0 to check the problem, and check the build log. Then I found the XCode uses "-isysroot" option in the link phase. According to GCC - Options for Directory Search, "--sysroot" option has a priority over "-isysroot", but it seems that "--sysroot" option is not working from XCode 4.0 and 3.2.6.

In any case, use '"-isysroot" option instead of "--sysroot" to run your configure scripts from XCode4 and 3.2.6 smile