Why doesn't gcov report any lines being covered by my unit tests?

Question

I am using Xcode 3.2 on 10.6, with the shipped version of gcov and default GCC compiler (both version 4.2.1). I have created a dependent Cocoa unit test bundle which is injected into my app, and followed Apple's documentation on setting up a gcov-instrumented build configuration - based on the Debug configuration which doesn't have any compiler optimisations enabled.

When I build the test bundle with this 'Gcov-instrumented' configuration, the app launches and the tests are injected and run. Also the coverage statistics files are generated at:

build/<AppTarget>.build/Gcov-instrumented/<AppTarget>.build/Objects-normal/x86_64/<object>.gcda

build/<AppTarget>.build/Gcov-instrumented/<AppTarget>.build/Objects-normal/x86_64/<object>.gcno

So far so good. I know the tests are really being run because if I insert failures then the test suite fails as expected. Unfortunately, gcov reports that no lines of the objects have been covered by the tests! Every line is reported as 0 coverage. I've searched here and at the Apple mailing list archives, and can't find anyone with a similar problem. I expect I'm missing something - but what is it?

Answer 1

I have been running into this problem intermittently. I stumbled into a good length of lucky time where it was "mostly working" in my main project. By mostly working I mean I was able to get coverage to show up, but with a little more pain than on 10.5. I had to aggressively delete the coverage files and rebuild in order to get any updates, for instance. Even in my "barely working" state, the compiler/runtime doesn't seem willing to overwrite an existing coverage data file.

I think I've stumbled back on to a working scenario. Voodoo for sure, and less than ideal:

1. Make sure the SDK is 10.6.
2. Make sure the deployment is set to gcc 4.0 (!).
3. Do a full clean of the project.
4. Rebuild.

Does this get you the expected coverage data?

Granted, I would expect to be able to generate coverage files that work using gcc 4.2 or one of the LLVM compilers, but for the moment this seems to have me slightly less crippled than before.

Another clue: when I observe the coverage data (using Google's Cover Story), I get warnings like:

/BUILDRESULTS/MarsEdit.build/Code Coverage/MarsEditDataModelTests.build/Objects-normal/i386/MEDataItem.gcno:version '400A', prefer '402*'

But the coverage information is still presented. So it seems it's balking at an older coverage format version, but if I use the newer compiler (4.2) which would presumably generate the newer format .gcno files, the 0% coverage problem plagues me as it does Graham.

Answer 2

In Xcode 4.6, coverage reports just seem to work. Turn on "Generate Test Coverage Files" and "Instrument Program Flow" for the app target, run the tests, then point the coverage tool at the output. That's in ~/Library/Developer/Xcode/Derived Data/<Project>-<hash>/Build/Intermediates/<Target>.build/Debug-iphonesimulator/<Target>.build; opening that folder in CoverStory shows me the results I expected.

This GitHub repository contains scripts that can automatically discover the output and get lcov to visualise it; I'm happy with CoverStory for now.

Answer 3

You can get code coverage working with gcc 4.2.1. Details here:

SnowLeopardGCov

Answer 4

I have been trying to get the Code coverage working for iPhone simulator and always get a 0% coverage. Below are the configuration details and the steps that I have tried.

Configuration

Xcode 3.2.5/iOS 4.1 and iOS 4.2/Mac 10.6/GCC 4.2 Application UICatalog

References

http://www.cubiclemuses.com/cm/articles/2009/05/14/coverstory-on-the-iphone/

http://developer.apple.com/library/mac/#qa/qa2007/qa1514.html

Steps

• Enable “Generate Test Coverage Files”
• Enable “Instrument Program Flow”
• Add “-lgcov” to “Other Linker Flags”
• UIApplicationExitsOnSuspend flag in Info.plist is set to true

Result

I have the .gcda files generated but the coverage always show 0%.

Settings tried

1. Changing GCC to 4.0 and 4.2. When I try to change the GCC to 4.0 I get 26 build errors.

2. Set environment variables:

   const char *prefix = "GCOV_PREFIX";
   const char *prefixValue = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] cStringUsingEncoding:NSASCIIStringEncoding]; // This gets the filepath to the app's Documents directory
   const char *prefixStrip = "GCOV_PREFIX_STRIP";
   const char *prefixStripValue = "1";
   setenv(prefix, prefixValue, 1); // This sets an environment variable which tells gcov where to put the .gcda files.
   setenv(prefixStrip, prefixStripValue, 1); // This tells gcov to strip the default prefix, and use the filepath that we just declared.)
   

3. GCC Optimization set to None (-O0) and unchecked the precompiled prefix header file flag.

Answer 5

I was getting 0 coverage when *.gcno files for static library was overwritten by those for shared library.