gcov: Add usage documentation

Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>

Documentation/applications/system/gcov/index.rst

@@ -1,3 +1,213 @@
 ==================
 ``gcov`` gcov tool
 ==================
+
+gcov is a tool for testing code coverage.
+After the program is run, you can view the line coverage, function coverage,
+and branch coverage of each file.
+
+Support
+-------
+
+The current system supports four code coverage detection implementations:
+
+1. GCC native implementation
+2. CLANG native implementation
+3. GCC coverage nuttx mini version
+4. CLANG coverage nuttx mini version
+
+The following table shows the specific differences between the four implementations
+ends 24.11.26：
+
+Support            GCC-native  CLANG-native     GCC-nuttx-mini      CLANG-nuttx-mini
+Compiler version:     ALL          ALL        GCC 13.2 and below   CLANG 17.0 and below
+
+Program coverage statistics support:
+
+Main Program           √            √                 √                     √
+Interrupt Program      ×            √                 √                     √
+
+Architecture Support:
+
+    arm                √            √                 √                     √
+    arm64              √            √                 √
+    riscv              √            √
+    X86_X64            √            √
+    xtensa             √            √
+    sim                √            √
+
+Usage
+=====
+
+App-Usage
+---------
+Usage::
+
+    gcov [-d path] [-t strip] [-r] [-h]
+
+Where:
+
+  -d dump the coverage, path is the path to the coverage file, the default output is to stdout
+  -t strip the path prefix number
+  -r reset the coverage
+  -h show this text and exits.
+
+Examples of applicable platforms
+--------------------------------
+
+1. SIM platform usage
+
+  1. Please enable the following config
+
+    # Support instrumentation of all codes in sim
+    1. CONFIG_COVERAGE_TOOLCHAIN=y
+
+    # Enable instrumentation
+    2. CONFIG_COVERAGE_ALL=y
+
+    # Enable gcov app
+    3. CONFIG_SYSTEM_GCOV=y
+
+  2. Compile and run
+     ```
+     $ After the code is compiled, a *.gcno file with the same name will be generated next to the *.o file.
+     $ After the compilation is completed, run the code to be tested, and exit the sim after the execution is completed
+     ```
+
+  3. Run the gcov app
+     ```
+     $ gcov -d path_to_gcno_file
+     ```
+
+  4. Check whether the generation is successful
+     ```
+     Execute the following command in the project root directory to check whether there is a gcda file generated (code coverage data)
+     find ./ -name "*.gcno"
+     find ./ -name "*.gcda"
+     ```
+
+2. Applicable to device
+
+  Due to differences in implementation methods, the device side is divided into GCC and CLANG
+
+  1. GCC
+
+    1. Please enable the following config
+
+      # Recommended to use nuttx mini version
+      CONFIG_COVERAGE_MINI=y
+
+      # Enable gcov app
+      CONFIG_SYSTEM_GCOV=y
+
+      # Please add different compilation options in makefile according to the compiler
+      CFLAGS += -fprofile-arcs -ftest-coverage -fno-inline
+
+    2. Run the gcov app
+       ```
+       $ gcov -d path_to_gcno_file
+       ```
+
+    3. Export data
+
+      After running the code on the device,
+      execute the gcov -d /tmp/gcov command in the nuttx command line
+      to save the generated data to the file system.
+      You need to use your method to export the file to the host
+
+    4. Generate Report
+
+      1. Install the tool
+
+        sudo apt install lcov
+
+      2. Generate report
+
+        Run the following command to generate coverage report
+
+        # By default, it is generated in the root directory of the vela project. Add parameters to specify the report generation location
+        # The -t parameter specifies the gcov version, which needs to match the gcc version
+
+        # sim
+        ./tools/gcov.sh -t gcov-13
+
+        # arm platform
+        ./tools/gcov.sh -t arm-none-eabi-gcov
+
+    5. Impact and precautions
+       ```
+       1. Before using the .tools/gcov.sh tool, you need to ensure that *.gcno and *.gcda files exist
+       2. If *.gcno does not exist, recompile the code after distclean.
+       3. If *.gcda does not exist, please check and use poweroff to exit Vela normally
+       ```
+
+  2. CLANG
+
+    # There is a ready-made defconfig in NXboards/arm/mps/mps3-an547/configs/gcov
+    # which can be used for reference
+
+    1. Please enable the following config
+
+      # Recommended to use nuttx mini version
+      CONFIG_COVERAGE_MINI=y
+
+      # Enable gcov app
+      CONFIG_SYSTEM_GCOV=y
+
+      # Please add different compilation options in makefile according to the compiler
+      CFLAGS += -fprofile-instr-generate -fcoverage-mapping
+
+    2. Modify the linker script
+
+      Please find the corresponding storage location in the link
+      script for the following data：
+
+      For detailed examples, please refer to boards/arm/mps/mps3-an547/scripts/flash.ld
+
+      .. code-block:: none
+
+          __llvm_prf_names : {
+              __start__llvm_prf_names = .;
+              KEEP (*(__llvm_prf_names))
+              __end__llvm_prf_names = .;
+          }
+
+          __llvm_prf_data : {
+              __start__llvm_prf_data = .;
+              KEEP (*(__llvm_prf_data))
+              __end__llvm_prf_data = .;
+          }
+
+          __llvm_prf_vnds : {
+              __start__llvm_prf_vnds = .;
+              KEEP (*(__llvm_prf_vnds))
+              __end__llvm_prf_vnds = .;
+          }
+
+          __llvm_prf_cnts : {
+              __start__llvm_prf_cnts = .;
+              KEEP (*(__llvm_prf_cnts))
+              __end__llvm_prf_cnts = .;
+          }
+
+
+    3. Run the gcov app
+
+      ```
+      $ gcov -d path_to_gcno_file
+      ```
+
+    4. Export data
+
+    5. Generate Report
+
+      Please execute the following command, where
+
+      1. xxxfile: the file for exporting data on the device
+      2. xxxelf: the ELF file corresponding to the device
+
+      # Convert the exported coverage data file
+      llvm-profdata merge -sparse xxxfile -o result.profdata
+
+      # Generate a visualization html file
+      llvm-cov show -format=html xxxelf -instr-profile=result.profdata -output-dir=./coverage/html