Re: [PATCH v2 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for LLVM=1 LLVM_IAS=1

[Linus Torvalds]

On Tue, Jul 20, 2021 at 2:54 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> But there are other things that stick around. In particular, I have
> considered simply using git config variables for that.
>
> Something like this in the main Makefile:

A slightly more fleshed-out patch to do this just to see if somebody
wants to work on something like this.

It really would seem to make it very easy to set up any random build
environment, and not have to remember it once it's done.

There are probably better ways to do this, I normally try to avoid
doing Makefile magic, since others have taken it over. Masahiro?

             Linus
 Makefile | 50 +++++++++++++++++++++++++++++++-------------------
 1 file changed, 31 insertions(+), 19 deletions(-)

diff --git a/Makefile b/Makefile
index e4f5895badb5..221eb205b475 100644
--- a/Makefile
+++ b/Makefile
@@ -436,27 +436,39 @@ KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
 KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 
-# Make variables (CC, etc...)
-CPP		= $(CC) -E
+# default build environment ('git config' can override)
 ifneq ($(LLVM),)
-CC		= clang
-LD		= ld.lld
-AR		= llvm-ar
-NM		= llvm-nm
-OBJCOPY		= llvm-objcopy
-OBJDUMP		= llvm-objdump
-READELF		= llvm-readelf
-STRIP		= llvm-strip
+DEF_CC		= clang
+DEF_LD		= ld.lld
+DEF_AR		= llvm-ar
+DEF_NM		= llvm-nm
+DEF_OBJCOPY	= llvm-objcopy
+DEF_OBJDUMP	= llvm-objdump
+DEF_READELF	= llvm-readelf
+DEF_STRIP	= llvm-strip
 else
-CC		= $(CROSS_COMPILE)gcc
-LD		= $(CROSS_COMPILE)ld
-AR		= $(CROSS_COMPILE)ar
-NM		= $(CROSS_COMPILE)nm
-OBJCOPY		= $(CROSS_COMPILE)objcopy
-OBJDUMP		= $(CROSS_COMPILE)objdump
-READELF		= $(CROSS_COMPILE)readelf
-STRIP		= $(CROSS_COMPILE)strip
-endif
+DEF_CC		= $(CROSS_COMPILE)gcc
+DEF_LD		= $(CROSS_COMPILE)ld
+DEF_AR		= $(CROSS_COMPILE)ar
+DEF_NM		= $(CROSS_COMPILE)nm
+DEF_OBJCOPY	= $(CROSS_COMPILE)objcopy
+DEF_OBJDUMP	= $(CROSS_COMPILE)objdump
+DEF_READELF	= $(CROSS_COMPILE)readelf
+DEF_STRIP	= $(CROSS_COMPILE)strip
+endif
+
+build-option = $(shell git config --default "$(2)" --get $(1) || echo "$(2)")
+CC		= $(call build-option,build.cc,$(DEF_CC))
+LD		= $(call build-option,build.ld,$(DEF_LD))
+AR		= $(call build-option,build.ar,$(DEF_AR))
+NM		= $(call build-option,build.nm,$(DEF_NM))
+OBJCOPY		= $(call build-option,build.objcopy,$(DEF_OBJCOPY))
+OBJDUMP		= $(call build-option,build.objdump,$(DEF_OBJDUMP))
+READELF		= $(call build-option,build.readelf,$(DEF_READELF))
+STRIP		= $(call build-option,build.strip,$(DEF_STRIP))
+
+# Make variables (CC, etc...)
+CPP		= $(CC) -E
 PAHOLE		= pahole
 RESOLVE_BTFIDS	= $(objtree)/tools/bpf/resolve_btfids/resolve_btfids
 LEX		= flex