[compiler-rt] Add baremetal version of profile library. (#167998)
Adds a flag COMPILER_RT_PROFILE_BAREMETAL, which disables the parts of
the profile runtime which require a filesystem or malloc. This minimal
library only requires string.h from the C library.
This is useful for profiling or code coverage of baremetal images, which
don't have filesystem APIs, and might not have malloc configured (or
have limited heap space).
Expected usage:
- Add code to your project to call
`__llvm_profile_get_size_for_buffer()` and
`__llvm_profile_write_buffer()` to write the profile data to a buffer in
memory, and then copy that data off the device using target-specific
tools.
- If you're using a linker script, set up your linker script to map the
profiling and coverage input sections to corresponding output sections
with the same name, and mark them KEEP. `__llvm_covfun` and
`__llvm_covmap` are non-allocatable, `__llvm_prf_names` is read-only
allocatable, and `__llvm_prf_cnts` and `__llvm_prf_data` are read-write
allocatable.
- The resulting data is in same format as the non-baremetal profiles.
There's some room for improvement here in the future for doing profiling
and code coverage for baremetal. If we revised the profiling format, and
introduced some additional host tooling, we could move some of the
metadata into non-allocated sections, and construct the profraw file on
the host. But this patch is sufficient for some use-cases.
NOKEYCHECK=True
GitOrigin-RevId: bc0d0bbc6b36445730067b6e302f332fa1e3fa35
10 files changed
