From 81eb7088b6ae1b3b14ed57ef428b1b9f74d468cf Mon Sep 17 00:00:00 2001 From: Bin Meng Date: Mon, 12 Jul 2021 09:20:16 +0800 Subject: [PATCH] README: Update toolchain information Recent FW_PIC=y changes actually require toolchains with PIE support and it is on by default. Existing doc uses a GNU bare-metal toolchain as examples but it does not support PIE. Replace references of bare-metal toolchain prefix with Linux toolchain prefix everywhere in documentation. Also indicate that "riscv64-unknown-freebsd-" as an alternative to "riscv64-linux-" GNU toolchain. Signed-off-by: Bin Meng Reviewed-by: Anup Patel --- README.md | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/README.md b/README.md index b296f00..9fdf097 100644 --- a/README.md +++ b/README.md @@ -104,6 +104,14 @@ 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. +Basically, we prefer toolchains with Position Independent Executable (PIE) +support like *riscv64-linux-gnu-gcc*, *riscv64-unknown-freebsd-gcc*, or +*Clang/LLVM* as they generate PIE firmware images that can run at arbitrary +address with appropriate alignment. If a bare-metal GNU toolchain (e.g. +*riscv64-unknown-elf-gcc*) is used, static linked firmware images are +generated instead. *Clang/LLVM* can still generate PIE images if a bare-metal +triple is used (e.g. *-target riscv64-unknown-elf*). + Please note that only a 64-bit version of the toolchain is available in the Bootlin toolchain repository for now. @@ -116,7 +124,7 @@ architecture than RISC-V. For cross-compiling, the environment variable *CROSS_COMPILE* must be defined to specify the name prefix of the RISC-V compiler toolchain executables, e.g. -*riscv64-unknown-elf-* if the gcc executable used is *riscv64-unknown-elf-gcc*. +*riscv64-linux-gnu-* if the gcc executable used is *riscv64-linux-gnu-gcc*. To build *libsbi.a* simply execute: ``` @@ -192,16 +200,16 @@ Building 32-bit / 64-bit OpenSBI Images --------------------------------------- By default, building OpenSBI generates 32-bit or 64-bit images based on the supplied RISC-V cross-compile toolchain. For example if *CROSS_COMPILE* is set -to *riscv64-unknown-elf-*, 64-bit OpenSBI images will be generated. If building +to *riscv64-linux-gnu-*, 64-bit OpenSBI images will be generated. If building 32-bit OpenSBI images, *CROSS_COMPILE* should be set to a toolchain that is -pre-configured to generate 32-bit RISC-V codes, like *riscv32-unknown-elf-*. +pre-configured to generate 32-bit RISC-V codes, like *riscv32-linux-gnu-*. However it's possible to explicitly specify the image bits we want to build with a given RISC-V toolchain. This can be done by setting the environment variable *PLATFORM_RISCV_XLEN* to the desired width, for example: ``` -export CROSS_COMPILE=riscv64-unknown-elf- +export CROSS_COMPILE=riscv64-linux-gnu- export PLATFORM_RISCV_XLEN=32 ``` @@ -235,7 +243,7 @@ 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 +make CC=riscv64-linux-gnu-gcc LLVM=1 ``` These variables must be passed for all the make invocations described in this -- 2.7.4