[PATCH] Makefile: Make $(LLVM) more flexible

[Jessica Clarke]

On 1 May 2025, at 00:38, Charlie Jenkins <charlie at rivosinc.com> wrote:
> 
> Introduce a way for developers to easily switch between LLVM versions
> with LLVM=/path/to/llvm/ and LLVM=-version. This is a useful

FreeBSD doesn’t include a hyphen in its version number suffix, you get
clang20 etc. In the Linux world where you’ve copied this pattern from
verbatim that may well hold, but OpenSBI supports more than just Linux.

One could special-case LLVM=1 and treat anything else as a suffix I
suppose, though that would be a little weird.

Jess

> addition to the existing LLVM=1 variable which will select the first
> clang and llvm binutils available on the path.
> 
> Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
> ---
> Makefile  | 14 ++++++++++----
> README.md | 12 ++++++++++++
> 2 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index e90836c7c4ad16c30d4d80649ff8b228413190ad..37d4cf41a2214e0a829f1d4a53f3f4f9ae09ee41 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -104,10 +104,16 @@ endif
> 
> # Setup compilation commands
> ifneq ($(LLVM),)
> -CC = clang
> -AR = llvm-ar
> -LD = ld.lld
> -OBJCOPY = llvm-objcopy
> +ifneq ($(filter %/,$(LLVM)),)
> +LLVM_PREFIX := $(LLVM)
> +else ifneq ($(filter -%,$(LLVM)),)
> +LLVM_SUFFIX := $(LLVM)
> +endif
> +
> +CC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> +AR = $(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX)
> +LD = $(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX)
> +OBJCOPY = $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX)
> else
> ifdef CROSS_COMPILE
> CC = $(CROSS_COMPILE)gcc
> diff --git a/README.md b/README.md
> index 2795cc1a5ff0df62d83a4b5c3062ff2b682dbcab..fd40be0b4988815d8d02386271aeaeb787541215 100644
> --- a/README.md
> +++ b/README.md
> @@ -252,6 +252,18 @@ option with:
> make LLVM=1
> ```
> 
> +To build with a specific version of LLVM, a path to a directory containing the
> +LLVM tools can be provided:
> +```
> +make LLVM=/path/to/llvm/
> +```
> +
> +If you have versioned llvm tools you would like to use, such as `clang-17`, the LLVM variable can
> +be set as:
> +```
> +make LLVM=-17
> +```
> +
> 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*
> 
> ---
> base-commit: 316daaf1c299c29ac46e52145f65521f48ec63b5
> change-id: 20250430-improve_llvm_building-cff31918e1a6
> -- 
> - Charlie
> 
> 
> -- 
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