Not able to build my project on xcode 4.2

问题

I have upgraded my xcode to 4.2 (using snow leopard).Previously i was using Xcode 3.2.6 and my project build successfully with it. Now I'm unable to build it, instead Xcode emits the following error

ld: warning: option -A is obsolete and being ignored
ld: entry point (start) undefined.  Usually in crt1.o for architecture armv7
Command /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/clang failed with exit code 1

The error seems to be some compiler error but can't figure it out .:( I googled for it but no luck yet. Please suggest some solution.

回答1:

It looks like linker is looking for a start function as entry point in crt1, but didn't find it. You can try adding a linker flag,

 -e symbol_name
    Specifies the entry point of a main executable.  By default the entry name is "start" which
    is found in crt1.o which contains the glue code need to set up and call main().

from the man page of ld.

回答2:

The first error means the linker (ld) in Xcode 4.2 encountered an option (-A) that is no longer supported.

If you no longer need to build the same Xcode project in Xcode 3.2.6 then

1. check your Project's Build Settings to ensure you don't have '-A' specified
   
   .
2. click on the "Validate Settings" button
   
   to identify any other project settings that may cause problem.

Your second error may be caused by Xcode 4.2 defaulting to armv7 build architecture that is unlisted your Xcode project (because it was built using Xcode 3.2.6). If you need to build binaries for armv6, then add that to your build architecture list.

回答3:

Check if you are using following flags, it will cause that error -nostdlib and -noconfig.

回答4:

I was able to fix this issue by updating the 'iOS Development Target' in my project's target > Build Settings

来源：https://stackoverflow.com/questions/7976516/not-able-to-build-my-project-on-xcode-4-2