one copy in the binary itself and anotherĬopy that’s mapped into memory). The disadvantage is the extra overhead due to additional instructions requiredįor each counter access (overhead both in terms of binary size and performance) The advantage of this approach is that doesn’t require any special OS support. Which allows updating profile directly akin to the continuous mode.
The runtime can map the profile into memory at arbitrary locations,Īnd set bias to the offset between the original and the new counter location,Īt which point every subsequent counter access will be to the new location, Provided by the profile runtime and is initially set to zero, meaning no This bias is stored in _llvm_profile_counter_bias symbol that’s On every counter access, we add a bias to the counterĪddress. On Fuchsia, we rely on the ability to relocate counters at runtime using a Mapping which is generally only available on POSIX systems and isn’t suitable Relies on padding and the ability to map a file over the existing memory Mode, but the implementation is different.
Note that continuous mode is also used on Fuchsia where it’s the only supported May require more extensive changes: please get involved if you are interested Linux may be mostly complete but requires testing, and support for Windows Profiling for PGO, and is only supported on Darwin at the moment. Instrumented program crashes, or is killed by a signal, perfect coverage Updates are continuously synced to a file. “%c” expands out to nothing, but enables a mode in which profile counter.The merge pool specifier can only occur once per filename Not specified (i.e the pattern is “%m”), it’s assumed that N = 1. The runtime takes care of selecting a raw profileįrom the pool, locking it, and updating it before the program exits. Is specified, the runtime creates a pool of N raw profiles which are used for “%Nm” expands out to the instrumented binary’s signature.Onĭarwin, this is typically set to a temporary scratch directory. “%t” expands out to the value of the TMPDIR environment variable.“%h” expands out to the hostname of the machine running the program.LLVM_PROFILE_FILE contains a path to a non-existent directory, the missingĭirectory structure will be created. To default.profraw in the current directory of the program. If that variable does not exist, the profile is written Will write a raw profile to the path specified by the LLVM_PROFILE_FILEĮnvironment variable. The next step is to run the instrumented program.
0 kommentar(er)
