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

[Charlie Jenkins]

On Thu, May 01, 2025 at 01:04:38AM +0100, Jessica Clarke wrote:
> 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.

This pattern not being applicable for all systems doesn't invalidate the
usecase for systems that do support it. Developers can still manipulate
their PATH to get LLVM=1 to select the clang that they want.

- Charlie

> 
> 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
> > 
> > 
> > -- 
> > opensbi mailing list
> > opensbi at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/opensbi
>