Makefile: Rename CROSS_COMPILE to CROSS_COMPILE_PREFIX

Make it clear what this environment variable defines and update
the README.md file to explain that.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>

Makefile

@@ -102,7 +102,7 @@ deps-y+=$(lib-objs-path-y:.o=.dep)
 deps-y+=$(firmware-objs-path-y:.o=.dep)
 
 # Setup compilation environment
-cpp=$(CROSS_COMPILE)cpp
+cpp=$(CROSS_COMPILE_PREFIX)cpp
 cppflags+=-DOPENSBI_MAJOR=$(MAJOR)
 cppflags+=-DOPENSBI_MINOR=$(MINOR)
 cppflags+=-I$(platform_dir)/include
@@ -110,7 +110,7 @@ cppflags+=-I$(platform_common_dir)/include
 cppflags+=-I$(include_dir)
 cppflags+=$(platform-cppflags-y)
 cppflags+=$(firmware-cppflags-y)
-cc=$(CROSS_COMPILE)gcc
+cc=$(CROSS_COMPILE_PREFIX)gcc
 cflags=-g -Wall -Werror -nostdlib -fno-strict-aliasing -O2
 cflags+=-fno-omit-frame-pointer -fno-optimize-sibling-calls
 cflags+=-mno-save-restore -mstrict-align
@@ -118,7 +118,7 @@ cflags+=$(cppflags)
 cflags+=$(platform-cflags-y)
 cflags+=$(firmware-cflags-y)
 cflags+=$(EXTRA_CFLAGS)
-as=$(CROSS_COMPILE)gcc
+as=$(CROSS_COMPILE_PREFIX)gcc
 asflags=-g -Wall -nostdlib -D__ASSEMBLY__
 asflags+=-fno-omit-frame-pointer -fno-optimize-sibling-calls
 asflags+=-mno-save-restore -mstrict-align
@@ -126,15 +126,15 @@ asflags+=$(cppflags)
 asflags+=$(platform-asflags-y)
 asflags+=$(firmware-asflags-y)
 asflags+=$(EXTRA_ASFLAGS)
-ar=$(CROSS_COMPILE)ar
+ar=$(CROSS_COMPILE_PREFIX)ar
 arflags=rcs
-ld=$(CROSS_COMPILE)gcc
+ld=$(CROSS_COMPILE_PREFIX)gcc
 ldflags=-g -Wall -nostdlib -Wl,--build-id=none
 ldflags+=$(platform-ldflags-y)
 ldflags+=$(firmware-ldflags-y)
-merge=$(CROSS_COMPILE)ld
+merge=$(CROSS_COMPILE_PREFIX)ld
 mergeflags=-r
-objcopy=$(CROSS_COMPILE)objcopy
+objcopy=$(CROSS_COMPILE_PREFIX)objcopy
 
 # Setup functions for compilation
 define dynamic_flags

README.md

@@ -28,8 +28,9 @@ We can create three things using the RISC-V OpenSBI project:
 How to Build?
 -------------
 
-For cross-compiling, please ensure that CROSS_COMPILE environment
-variable is set before starting build system.
+For cross-compiling, the environment variable CROSS_COMPILE_PREFIX must be
+defined to specify the toolchain executable name prefix, e.g.
+"riscv64-unknown-elf-" for riscv64-unknown-elf-gcc.
 
 The libplatsbi.a and firmwares are optional and only built when
 `PLATFORM=<platform_subdir>` parameter is specified to top-level make.
@@ -78,4 +79,4 @@ We also prefer source level documentation, so wherever possible we describe
 stuff directly in the source code. This helps us maintain source and its
 documentation at the same place. For source level documentation we strictly
 follow Doxygen style. Please refer [Doxygen manual]
-(http://www.stack.nl/~dimitri/doxygen/manual.html) for details.
+(http://www.stack.nl/~dimitri/doxygen/manual.html) for details.