doc: Update toolchain build doc

Change-Id: I44acf6b308b28e76a293e8d88bd48840a33d38eb

BuildRiscVToolchain.md

diff --git a/BuildRiscVToolchain.md b/BuildRiscVToolchain.md
index fef1138..0f91330 100644
--- a/BuildRiscVToolchain.md
+++ b/BuildRiscVToolchain.md
@@ -5,6 +5,7 @@
 libraries, and LLVM to build the compiler, linker, and utility tools.
 
 ## Prerequisites
+
 Your host machine needs to have the following packages installed, which are
 already part of the Shodan prerequisite pacakges
 
@@ -13,16 +14,18 @@
 * Clang
 
 The source code of the toolchain is at
+
 * [riscv-gnu-toolchain](https://github.com/riscv/riscv-gnu-toolchain): Checkout
-the latest release tag, and checkout the submodule `riscv-binutils` with the
-`rvv-1.0.x-zfh` branch.
+the latest release tag, and checkout the submodule `riscv-binutils` at the master
+branch at git://sourceware.org/git/binutils-gdb.git
 * [llvm-project](https://github.com/llvm/llvm-project): Checkout the latest green
 commit
 
 ## Build RISC-V Linux toolchain (64-bit)
 
-### Build GCC:
-```
+### Build GCC
+
+```bash
 $ mkdir -p <GCC_BUILD_PATH>
 $ cd <GCC_BUILD_PATH>
 $ <GCC_SRC_PATH>/configure \
@@ -33,79 +36,88 @@
   --with-cmodel=medany
 $ make -C <GCC_BUILD_PATH> linux
 ```
+
 Notice Linux requires the full general CPU extension support, i.e., rv64imafdc,
 and the ABI also needs to support hard double-float modules. For 32-bit Linux,
 build the toolchain with the flags of `--with-arch=rv32gc --with-abi=ilp32d`.
 
-### Build LLVM:
-```
+### Build LLVM
+
+```bash
 $ cmake -B <LLVM_BUILD_PATH> \
-		-DCMAKE_INSTALL_PREFIX=<TOOLCHAIN_OUT_DIR> \
-		-DCMAKE_C_COMPILER=clang  -DCMAKE_CXX_COMPILER=clang++ \
-		-DCMAKE_BUILD_TYPE=Release \
-		-DLLVM_TARGETS_TO_BUILD="RISCV" \
-		-DLLVM_ENABLE_PROJECTS="clang"  \
-		-DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-linux-gnu" \
-		-DLLVM_INSTALL_TOOLCHAIN_ONLY=On \
-		-DDEFAULT_SYSROOT=../sysroot \
-		-G Ninja \
-		<LLVM_SRC_PATH>/llvm
+    -DCMAKE_INSTALL_PREFIX=<TOOLCHAIN_OUT_DIR> \
+    -DCMAKE_C_COMPILER=clang  -DCMAKE_CXX_COMPILER=clang++ \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DLLVM_TARGETS_TO_BUILD="RISCV" \
+    -DLLVM_ENABLE_PROJECTS="clang"  \
+    -DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-linux-gnu" \
+    -DLLVM_INSTALL_TOOLCHAIN_ONLY=On \
+    -DDEFAULT_SYSROOT=../sysroot \
+    -G Ninja \
+    <LLVM_SRC_PATH>/llvm
 $ cmake --build  <LLVM_BUILD_PATH> --target install
 ```
+
 For 32-bit, change the LLVM target triple to `riscv32-unknown-linux-gnu`.
 
 ## Build RISC-V bare-metal toolchain (32-bit)
 
-### Build GCC:
-```
+### Build 32-bit GCC
+
+```bash
 $ mkdir -p <GCC_BUILD_PATH>
 $ cd <GCC_BUILD_PATH>
 $ <GCC_SRC_PATH>/configure \
   --srcdir=<GCC_SRC_PATH> \
   --prefix=<TOOLCHAIN_OUT_DIR> \
-  --with-arch=rv32gc \
+  --with-arch=rv32i2p0mf2p0 \
   --with-abi=ilp32 \
   --with-cmodel=medany
 $ make -C <GCC_BUILD_PATH> newlib
 ```
+
 Notice for bare-metal newlib there's no hard constraints on CPU feature and ABI
 support. However, LLVM for bare-metal only supports soft-float modules, so the
-GCC ABI setting needs to match that.
+GCC ABI setting needs to match that. Also, the ISA version needs to be specified,
+since binuils ISA supports 20191213 spec and LLVM is at v2.2 spec
 
-### Build LLVM:
-```
+### Build 32-bit LLVM
+
+```bash
 $ cmake -B <LLVM_BUILD_PATH> \
-		-DCMAKE_INSTALL_PREFIX=<TOOLCHAIN_OUT_DIR> \
-		-DCMAKE_C_COMPILER=clang  -DCMAKE_CXX_COMPILER=clang++ \
-		-DCMAKE_BUILD_TYPE=Release \
-		-DLLVM_TARGETS_TO_BUILD="RISCV" \
-		-DLLVM_ENABLE_PROJECTS="clang"  \
-		-DLLVM_DEFAULT_TARGET_TRIPLE="riscv32-unknown-elf" \
-		-DLLVM_INSTALL_TOOLCHAIN_ONLY=On \
-		-DDEFAULT_SYSROOT=../riscv32-unknown-elf \
-		-G Ninja \
-		<LLVM_SRC_PATH>/llvm
+    -DCMAKE_INSTALL_PREFIX=<TOOLCHAIN_OUT_DIR> \
+    -DCMAKE_C_COMPILER=clang  -DCMAKE_CXX_COMPILER=clang++ \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DLLVM_TARGETS_TO_BUILD="RISCV" \
+    -DLLVM_ENABLE_PROJECTS="clang"  \
+    -DLLVM_DEFAULT_TARGET_TRIPLE="riscv32-unknown-elf" \
+    -DLLVM_INSTALL_TOOLCHAIN_ONLY=On \
+    -DDEFAULT_SYSROOT=../riscv32-unknown-elf \
+    -G Ninja \
+    <LLVM_SRC_PATH>/llvm
 $ cmake --build  <LLVM_BUILD_PATH> --target install
 ```
+
 #### Build compiler-rt
 
 This should not be necessary for the Shodan usage, but in case the compiler-rt
-builtins is required in the project, it can be built with the additional commands
+builtins is required in the project (instead of using libgcc), it can be built
+with the additional commands:
 
-```
+```bash
 $ export PATH=<TOOLCHAIN_OUT_DIR>/bin:${PATH}
-$ cmake -B <LLVM_BUILD_PATH>/compiler-rt
+$ cmake -B <LLVM_BUILD_PATH>/compiler-rt \
   -DCMAKE_INSTALL_PREFIX=$PREFIX \
   -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY \
   -DCMAKE_AR=<TOOLCHAIN_OUT_DIR>/bin/llvm-ar \
   -DCMAKE_NM=<TOOLCHAIN_OUT_DIR>/bin/llvm-nm \
   -DCMAKE_RANLIB=<TOOLCHAIN_OUT_DIR>/bin/llvm-ranlib \
-  -DCMAKE_C_FLAGS="-march=rv32gc" \
-  -DCMAKE_ASM_FLAGS="-march=rv32gc" \
+  -DCMAKE_C_FLAGS="-march=rv32i2p0mf2p0v1p0" \
+  -DCMAKE_ASM_FLAGS="-march=rv32i2p0mf2p0v1p0" \
   -DCMAKE_C_COMPILER=<TOOLCHAIN_OUT_DIR>/bin/clang \
   -DCMAKE_C_COMPILER_TARGET=riscv32-unknown-elf \
   -DCMAKE_ASM_COMPILER_TARGET=riscv32-unknown-elf \
-  -DCOMPILER_RT_OS_DIR="clang/13.0.0/lib" \
+  -DCOMPILER_RT_OS_DIR="clang/14.0.0/lib" \
   -DCMAKE_EXE_LINKER_FLAGS="-fuse-ld=lld" \
   -DCOMPILER_RT_BUILD_BUILTINS=ON \
   -DCOMPILER_RT_BUILD_SANITIZERS=OFF \
@@ -116,19 +128,21 @@
   -DCOMPILER_RT_BAREMETAL_BUILD=ON \
   -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON \
   -DLLVM_CONFIG_PATH=<LLVM_BUILD_PATH>/bin/llvm-config \
-  -DCMAKE_C_FLAGS="-march=rv32gc -mno-relax" \
-  -DCMAKE_ASM_FLAGS="-march=gv32gc -mno-relax" \
+  -DCMAKE_C_FLAGS="-march=rv32i2p0mf2p0v1p0 -mno-relax" \
+  -DCMAKE_ASM_FLAGS="-march=rv32i2p0mf2p0v1p0 -mno-relax" \
   -G "Ninja" <LLVM_SRC_PATH>/compiler-rt
 $ cmake --build <LLVM_BUILD_PATH>/compiler-rt --target install
 ```
 
 ### Build newlib
 
-The source code is at https://github.com/riscv/riscv-newlib
+Even with compiler_rt to replace libgcc, we still need to build libc, libm, and
+libgloss as the toolchain prebuilts. They can also be built with clang
+The source code is at <https://github.com/riscv/riscv-newlib>
 
 ***NOTE: The GCC utility tools needs to be built first.***
 
-```
+```bash
 $ mkdir -p <NEWLIB_BUILD_PATH>
 $ cd <NEWLIB_BUILD_PATH>
 $ <NEWLIB_SRC_PATH>/configure \
@@ -140,23 +154,29 @@
   --enable-newlib-register-fini \
   CC_FOR_TARGET=clang \
   CXX_FOR_TARGET=clang++ \
-  CFLAGS_FOR_TARGET="-march=rv32gc -O2 -D_POSIX_MODE -mno-relax" \
-  CXXFLAGS_FOR_TARGET="-march=rv32gc -O2 -D_POSIX_MODE -mno-relax"
+  CFLAGS_FOR_TARGET="-march=rv32i2p0mf2p0v1p0 -O2 -D_POSIX_MODE -mno-relax" \
+  CXXFLAGS_FOR_TARGET="-march=rv32i2p0mf2p0v1p0 -O2 -D_POSIX_MODE -mno-relax"
 $ make -j32
 $ make install
 ```
+
+The newlib nano spec needs to be built separatedly and then merged with newlib.
+GNU top-level Makefile lists the flags to build nano and the merging script.
+
 ## Test toolchain
 
 Run
-```
+
+```bash
 <TOOLCHAIN_OUT_DIR>/bin/<arch>-<os>-<abi>-gcc -v
 ```
+
 to see the supported ABIs, architectures, library paths, etc.
 
 Try to compile a simple c code (copied from CMake's package content, e.g.,
 `/usr/share/cmake-3.18/Modules/CMakeTestCCompiler.cmake`)
 
-```
+```c
 #ifdef __cplusplus
 # error "The CMAKE_C_COMPILER is set to a C++ compiler"
 #endif
@@ -169,11 +189,13 @@
 #endif
 { (void)argv; return argc-1;}
 ```
+
 To build (32-bit bare-metal example)
 
+```bash
+$<TOOLCHAIN_OUT_DIR>/bin/clang -c testCCompiler.c -O --target=riscv32
+$<TOOLCHAIN_OUT_DIR>/bin/riscv32-unknown-elf-gcc testCCompiler.o -o testCCompiler -march=rv32gc -mabi=ilp32
 ```
-$ <TOOLCHAIN_OUT_DIR>/bin/clang -c testCCompiler.c -O --target=riscv32
-$ <TOOLCHAIN_OUT_DIR>/bin/riscv32-unknown-elf-gcc testCCompiler.o -o testCCompiler -march=rv32gc -mabi=ilp32
-```
+
 You can also use `readelf` to inspect the object file before building the binary
 to see if the architecture and ABI match.