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Coverage: Document how to collect a profile without a filesystem 

The profiling runtime was designed to work without static initializers
or a a filesystem (see 117cf2bd1f and
others). The no-static-initializers part was already documented but this
part got missed before.

Differential Revision: https://reviews.llvm.org/D101000
This commit is contained in:
Duncan P. N. Exon Smith 2021-04-21 15:00:51 -07:00
parent 832340ca87
commit d4ee603c8f
1 changed files with 28 additions and 0 deletions
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clang/docs/SourceBasedCodeCoverage.rst
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@ -346,6 +346,34 @@ without using static initializers, do this manually:
In C++ files, declare these as ``extern "C"``.
Using the profiling runtime without a filesystem
------------------------------------------------
The profiling runtime also supports freestanding environments that lack a
filesystem. The runtime ships as a static archive that's structured to make
dependencies on a hosted environment optional, depending on what features
the client application uses.
The first step is to export ``__llvm_profile_runtime``, as above, to disable
the default static initializers. Instead of calling the ``*_file()`` APIs
described above, use the following to save the profile directly to a buffer
under your control:
* Forward-declare ``uint64_t __llvm_profile_get_size_for_buffer(void)`` and
call it to determine the size of the profile. You'll need to allocate a
buffer of this size.
* Forward-declare ``int __llvm_profile_write_buffer(char *Buffer)`` and call it
to copy the current counters to ``Buffer``, which is expected to already be
allocated and big enough for the profile.
* Optionally, forward-declare ``void __llvm_profile_reset_counters(void)`` and
call it to reset the counters before entering a specific section to be
profiled. This is only useful if there is some setup that should be excluded
from the profile.
In C++ files, declare these as ``extern "C"``.
Collecting coverage reports for the llvm project
================================================