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| <title>Using the GNU Compiler Collection (GCC): Cross-profiling</title> |
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| <a name="Data-file-relocation-to-support-cross_002dprofiling"></a> |
| <h3 class="section">10.5 Data file relocation to support cross-profiling</h3> |
| |
| <p>Running the program will cause profile output to be generated. For each |
| source file compiled with <samp>-fprofile-arcs</samp>, an accompanying <samp>.gcda</samp> |
| file will be placed in the object file directory. That implicitly requires |
| running the program on the same system as it was built or having the same |
| absolute directory structure on the target system. The program will try |
| to create the needed directory structure, if it is not already present. |
| </p> |
| <p>To support cross-profiling, a program compiled with <samp>-fprofile-arcs</samp> |
| can relocate the data files based on two environment variables: |
| </p> |
| <ul> |
| <li> GCOV_PREFIX contains the prefix to add to the absolute paths |
| in the object file. Prefix can be absolute, or relative. The |
| default is no prefix. |
| |
| </li><li> GCOV_PREFIX_STRIP indicates the how many initial directory names to strip off |
| the hardwired absolute paths. Default value is 0. |
| |
| <p><em>Note:</em> If GCOV_PREFIX_STRIP is set without GCOV_PREFIX is undefined, |
| then a relative path is made out of the hardwired absolute paths. |
| </p></li></ul> |
| |
| <p>For example, if the object file <samp>/user/build/foo.o</samp> was built with |
| <samp>-fprofile-arcs</samp>, the final executable will try to create the data file |
| <samp>/user/build/foo.gcda</samp> when running on the target system. This will |
| fail if the corresponding directory does not exist and it is unable to create |
| it. This can be overcome by, for example, setting the environment as |
| ‘<samp>GCOV_PREFIX=/target/run</samp>’ and ‘<samp>GCOV_PREFIX_STRIP=1</samp>’. Such a |
| setting will name the data file <samp>/target/run/build/foo.gcda</samp>. |
| </p> |
| <p>You must move the data files to the expected directory tree in order to |
| use them for profile directed optimizations (<samp>--use-profile</samp>), or to |
| use the <code>gcov</code> tool. |
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