diff options
Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 48 |
1 files changed, 46 insertions, 2 deletions
@@ -96,8 +96,13 @@ Required Toolchain ------------------ OpenSBI can be compiled natively or cross-compiled on a x86 host. For -cross-compilation, you can build your own toolchain or just download -a prebuilt one from the [Bootlin toolchain repository]. +cross-compilation, you can build your own toolchain, download a prebuilt one +from the [Bootlin toolchain repository] or install a distribution-provided +toolchain; if you opt to use LLVM/Clang, most distribution toolchains will +support cross-compiling for RISC-V using the same toolchain as your native +LLVM/Clang toolchain due to LLVM's ability to support multiple backends in the +same binary, so is often an easy way to obtain a working cross-compilation +toolchain. Please note that only a 64-bit version of the toolchain is available in the Bootlin toolchain repository for now. @@ -202,6 +207,45 @@ export PLATFORM_RISCV_XLEN=32 will generate 32-bit OpenSBI images. And vice vesa. +Building with Clang/LLVM +------------------------ + +OpenSBI can also be built with Clang/LLVM. To build with just Clang but keep +the default binutils (which will still use the *CROSS_COMPILE* prefix if +defined), override the *CC* make variable with: +``` +make CC=clang +``` + +To build with a full LLVM-based toolchain, not just Clang, enable the *LLVM* +option with: +``` +make LLVM=1 +``` + +When using Clang, *CROSS_COMPILE* often does not need to be defined unless +using GNU binutils with prefixed binary names. *PLATFORM_RISCV_XLEN* will be +used to infer a default triple to pass to Clang, so if *PLATFORM_RISCV_XLEN* +itself defaults to an undesired value then prefer setting that rather than the +full triple via *CROSS_COMPILE*. If *CROSS_COMPILE* is nonetheless defined, +rather than being used as a prefix for the executable name, it will instead be +passed via the `--target` option with the trailing `-` removed, so must be a +valid triple. + +These can also be mixed; for example using a GCC cross-compiler but LLVM +binutils would be: +``` +make CC=riscv64-unknown-elf-gcc LLVM=1 +``` + +These variables must be passed for all the make invocations described in this +document. + +NOTE: Using Clang with a `riscv*-linux-gnu` GNU binutils linker has been seen +to produce broken binaries with missing relocations; it is therefore currently +recommended that this combination be avoided or *FW_PIC=n* be used to disable +building OpenSBI as a position-independent binary. + Contributing to OpenSBI ----------------------- |