Compiler API
Introduction
Here's the proposed compiler interface for the system and for people. FreeBSD will support compiling itself with different compilers, and may support having multiple compilers in the base system. FreeBSD will support using external compilers to build the base, even if they aren't in the base (eg, building FreeBSD with gcc 4.6 or with some chip vendor's special compiler).
User Interface
Users control which compiler is used based on a few variables.
| Variable | Values | Meaning |
| SYSTEM_COMPILER | gcc or clang | The class of compiler that is installed as ${CC} |
| GCC_VERSION | 421 | gcc 4.2.1 – The version of the gcc compiler being used |
| CLANG_VERSION | 311 | clang 3.1.1 – The version of the clang compiler installed |
| EXT_COMP | armv6-freebsd- or /usr/local/fred/bin/ | Used to specify the location of the compiler (but not what kind of compiler it actually is). If this is set, then the external compiler is used. Otherwise the bootstrap default system compiler is used. The external compiler is really the entire external toolchain. |
Programmer Interface
Generally, the traditional names for the C compiler, etc are used for the defaults. The above variables would be used something like the following:
.if ${SYSTEM_COMPILER} == "gcc"
CFLAGS += -Wall
.endif
.if ${SYSTEM_COMPILER} == "clang"
CFLAGS += -Weverything
.endif
.if ${SYSTEM_COMPILER} == "gcc" && ${GCC_VERSION} < 421
CFLAGS += -Wno-turtle-graphics
.endif
Most of the yucky part of this will live in a file, bsd.compiler.mk, that will be used to keep things contained. Some individual makefiles might need tweaks, however, based on what they are compiling.
bsd.compiler.mk
This file will hold all the common code for supporting different compilers. It is somewhat similar to bsd.cpu.mk which is compiler support for optimizing for specific CPUs, but more general. It may be possible to use bsd.cpu.mk for this, or rename it to bsd.compiler.mk.
External Compiler support
For an external compiler to work, it needs to have the following binaries in its bin directory (optionally, it can install all its binaries with a unique prefix too, so where it says 'cc' 'as' etc below, you could have 'armv6-freebsd-cc' 'armv6-freebsd-as' etc.
| Program | Purpose |
| ar | Archiver |
| as | Assembler |
| c++ | C++ Compiler |
| cc | C Compiler |
| cpp | C preprocessor stage |
| ld | loader |
| nm | symbol name reporter |
| objcopy | copy binary sections around |
| ranlib | Library indexing program |
| size | Report the size of the different sections of the binary |
| strip | Remove symbols from the binary |
The following are optional…
| Program | Purpose |
| addr2line | Convert an address to a line number |
| CC | C++ Compiler – historically present |
| c++filt | demangle C++ names. Not directly used in the FreeBSD build |
| g++ | Gnu name for c++ compiler |
| gcpp | Gnu name for c preprossor |
| gcov | Coverage tool |
| gnu-ar | Gnu interface ar |
| gnu-ranlib | Gnu interface to ranlib the library indexing program |
| objdump | examine the contents of binaries |
| readelf | another binary manipulation program |
| strings | extract any printable strings from the binary |