Port proflib.c to LLVM-18 INSTR_PROF_RAW_VERSION 9 (#422)

There have been a number of changes to the profile output since
LLVM17 that need to be taken account of:

* ELF targets no longer do self-registration.
* The profile version has been raised to 9.

In addition we want the sample to visualize the profile with
the run command so that we can more easily be alerted to
changes in the profile format.

The largest change is the removal of self-registration. When
this was in operation each object file has a .init_array entry
with a pointer to a registration function that would be called
prior to main. This registration function would register the
names and counters of all the functions, allowing the program
to calculate at run-time the extent of the counter and names
section. Without self-registration we need to use
linker defined __start_ and __stop_ section symbols to find
the extent.

The profile version increasing to 9 has added a bitmap section
that we need to account for. This section should be empty unless
MC/DC coverage is used.

The majority of the source code has been adapted from files in
llvm-project/compiler-rt/lib/profile and
llvm-project/compiler-rt/include/profile

To replicate the behaviour of the previous example, we make
a C __attribute__((constructor)) function that runs before
main to register an atexit handler that writes out the
profile after exiting main.

Author: smithp35

samples/src/cpp-baremetal-semihosting-prof/Makefile

@@ -28,14 +28,12 @@ hello.elf: *.cpp
 
 run: hello.hex
 	qemu-system-arm -M microbit -semihosting -nographic -device loader,file=$<
+	$(BIN_PATH)/llvm-profdata merge -sparse default.profraw -o hello.profdata
+	$(BIN_PATH)/llvm-cov show hello.elf -instr-profile=hello.profdata
 
 debug: hello.hex
 	qemu-system-arm -M microbit -semihosting -nographic -device loader,file=$< -s -S
 
-prof: run
-	llvm-profdata merge -sparse default.profraw -o hello.profdata
-	llvm-cov show hello.elf -instr-profile=hello.profdata
-
 clean:
 	rm -f *.elf *.hex *.profraw *.profdata *.o
 

samples/src/cpp-baremetal-semihosting-prof/README.md

@@ -1,10 +1,10 @@
 # Code profiling and coverage sample
 
-This sample shows how to use instrumentation to emit profile data 
+This sample shows how to use instrumentation to emit profile data
 and use it to show code coverage.
 
 Use `make run` to build with instrumentation, run and collect the raw profile data,
-then `make prof` to visualize the code coverage.
+then output a visualization of the code coverage.
 
 NOTE: The upstream runtime implementation changes regularly,
 thus `proflib.c` file needs to be updated to keep in sync.

samples/src/cpp-baremetal-semihosting-prof/make.bat

@@ -22,7 +22,6 @@
 :make
 @if [%target%]==[build] goto :build
 @if [%target%]==[run] goto :run
-@if [%target%]==[prof] goto :prof
 @if [%target%]==[clean] goto :clean
 @echo Error: unknown target "%target%"
 @exit /B 1
@@ -38,9 +37,6 @@
 @call :build_fn
 :do_run
 qemu-system-arm.exe -M microbit -semihosting -nographic -device loader,file=hello.hex
-@exit /B
-
-:prof
 llvm-profdata.exe merge -sparse default.profraw -o hello.profdata
 llvm-cov.exe show hello.elf -instr-profile=hello.profdata
 @exit /B