Xtensa lld update

[gerekon]

Hi @aykevl!

If you have time and want to test your LLD port with our LLVM toolchain release (partially based on GCC currently). Here are commits to help testing your Xtensa LLD with IDF. After building clang and LLD you can replace binaries in our latest release distro and use it to build IDF hello-world.
To build IDF example you need to add -fuse-ld=lld option to clang in IDF cmake file. Below is the example patch.

diff --git a/tools/cmake/toolchain-clang-esp32.cmake b/tools/cmake/toolchain-clang-esp32.cmake
index 1ed08504365..89a185cf957 100644
--- a/tools/cmake/toolchain-clang-esp32.cmake
+++ b/tools/cmake/toolchain-clang-esp32.cmake
@@ -13,13 +13,13 @@ set(CMAKE_OBJDUMP xtensa-esp32-elf-objdump)
 # -freestanding is a hack to force Clang to use its own stdatomic.h,
 # without falling back to the (incompatible) GCC stdatomic.h
 # https://github.com/espressif/llvm-project/blob/d9341b81/clang/lib/Headers/stdatomic.h#L13-L18
-remove_duplicated_flags("--target=xtensa -mcpu=esp32 -ffreestanding ${CMAKE_C_FLAGS}"
+remove_duplicated_flags("--target=xtensa -mcpu=esp32 -ffreestanding -fuse-ld=lld ${CMAKE_C_FLAGS}"
                         UNIQ_CMAKE_C_FLAGS)
 set(CMAKE_C_FLAGS "${UNIQ_CMAKE_C_FLAGS}"
     CACHE STRING "C Compiler Base Flags"
     FORCE)
 
-remove_duplicated_flags("--target=xtensa -mcpu=esp32 -ffreestanding ${CMAKE_CXX_FLAGS}"
+remove_duplicated_flags("--target=xtensa -mcpu=esp32 -ffreestanding -fuse-ld=lld ${CMAKE_CXX_FLAGS}"
                         UNIQ_CMAKE_CXX_FLAGS)
 set(CMAKE_CXX_FLAGS "${UNIQ_CMAKE_CXX_FLAGS}"
     CACHE STRING "C++ Compiler Base Flags"

Command to build IDF example should look like PATH=/tmp/xtensa-esp32-elf-clang/bin:$PATH IDF_TOOLCHAIN=clang idf.py build

[gerekon]

cc @andreisfr @igrr

[aykevl]

Sorry for the delay!

Unfortunately I still can't get it working. I've done the following:

• built LLVM at 2b94f6d
• downloaded the latest build from https://github.com/espressif/llvm-project/releases/tag/esp-13.0.0-20211203
• copied clang-13 and lld binaries into the xtensa-esp32-elf-clang/bin directory
• checked out esp-idf at v4.4.1 (1329b19fe494500aeb79d19b27cfd99b40c37aec)
• ran install.fish
• copied the hello_world example to a new location
• patched esp-idf as above (but slightly differently, see patch below)
• ran env PATH="/home/ayke/lib/xtensa-esp32-elf-clang-modified/bin:$PATH" IDF_TOOLCHAIN=clang idf.py build (using the fish shell)

Unfortunately it doesn't quite work yet. This is the error I'm getting:

Executing action: all (aliases: build)
Running cmake in directory /home/ayke/tmp/hello_world/build
Executing "cmake -G Ninja -DPYTHON_DEPS_CHECKED=1 -DESP_PLATFORM=1 -DCCACHE_ENABLE=0 /home/ayke/tmp/hello_world"...
-- IDF_TARGET not set, using default target: esp32
-- Found Git: /usr/bin/git (found version "2.30.2") 
-- Component directory /home/ayke/src/esp-idf/components/ethernet does not contain a CMakeLists.txt file. No component will be added
-- The C compiler identification is Clang 13.0.0
-- The CXX compiler identification is Clang 13.0.0
-- The ASM compiler identification is Clang
-- Found assembler: /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - failed
-- Check for working C compiler: /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang
-- Check for working C compiler: /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang - broken
CMake Error at /usr/share/cmake-3.18/Modules/CMakeTestCCompiler.cmake:66 (message):
  The C compiler

    "/home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: /home/ayke/tmp/hello_world/build/CMakeFiles/CMakeTmp
    
    Run Build Command(s):/usr/bin/ninja cmTC_51375 && [1/2] Building C object CMakeFiles/cmTC_51375.dir/testCCompiler.c.obj
    clang-13: warning: argument unused during compilation: '-fuse-ld=lld' [-Wunused-command-line-argument]
    [2/2] Linking C executable cmTC_51375
    FAILED: cmTC_51375 
    : && /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang --target=xtensa -mcpu=esp32 -ffreestanding -fuse-ld=lld  CMakeFiles/cmTC_51375.dir/testCCompiler.c.obj -o cmTC_51375   && :
    clang-13: error: invalid linker name in argument '-fuse-ld=lld'
    ninja: build stopped: subcommand failed.

To be absolutely sure I used the correct Clang version I ran the following command:

$ /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin/clang --version
clang version 13.0.0 (git@github.com:tinygo-org/llvm-project.git 2b94f6dd356894ad5f0199d595d40eabd01036fd)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/ayke/lib/xtensa-esp32-elf-clang-modified/bin

The git hash matches.

This is the patch I've been using for esp-idf:

diff --git a/tools/cmake/toolchain-clang-esp32.cmake b/tools/cmake/toolchain-clang-esp32.cmake
index bb25f98298..3b84307f06 100644
--- a/tools/cmake/toolchain-clang-esp32.cmake
+++ b/tools/cmake/toolchain-clang-esp32.cmake
@@ -11,6 +11,6 @@ set(CMAKE_OBJDUMP xtensa-esp32-elf-objdump)
 # -freestanding is a hack to force Clang to use its own stdatomic.h,
 # without falling back to the (incompatible) GCC stdatomic.h
 # https://github.com/espressif/llvm-project/blob/d9341b81/clang/lib/Headers/stdatomic.h#L13-L18
-set(CMAKE_C_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding" CACHE STRING "C++ Compiler Base Flags")
+set(CMAKE_C_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding -fuse-ld=lld" CACHE STRING "C Compiler Base Flags")
+set(CMAKE_CXX_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding -fuse-ld=lld" CACHE STRING "C++ Compiler Base Flags")
 set(CMAKE_ASM_FLAGS "--target=xtensa -mcpu=esp32" CACHE STRING "Assembler Base Flags")

[aykevl]

I think I got it working! I had to create an ld.lld link pointing to lld. I'm now hitting "unknown opcode for relocation" errors, which is what I want.