Building only gcc using yocto - yocto

Question

I was trying to build only gcc using yocto. I tried with "bitbake-layers show-recipes" it was showing multiple recipes for gcc, similarly for bitbake -s.
#bitbake-layers show-recipes
gcc:
meta 4.8.2
gcc-cross:
meta 4.8.2
gcc-cross-canadian-arm:
meta 4.8.2
gcc-cross-initial:
meta 4.8.2
gcc-crosssdk:
meta 4.8.2
gcc-crosssdk-initial:
meta 4.8.2
gcc-runtime:
meta 4.8.2
gccmakedep:
meta 1:1.0.2
#bitbake -s
gcc :4.8.2-r0
gcc-cross :4.8.2-r0
gcc-cross-canadian-arm :4.8.2-r0
gcc-cross-initial :4.8.2-r0
gcc-crosssdk :4.8.2-r0
gcc-crosssdk-initial :4.8.2-r0
gcc-runtime :4.8.2-r0
gccmakedep 1:1.0.2-r3
Please guide me to understand why there are multiple recipes related to gcc and which one I have to build.
In yocto, is there one to one match for recipe and package. i.e for creating each package there is a corresponding only one recipe?

Answer 1

To explain each one in turn:
gcc is the recipe for gcc that runs on the target machine itself.
gcc-cross is the cross-compiler that the build system uses. If you build any recipe for the target that needs to be compiled with gcc, this is what will be used to compile that.
gcc-cross-canadian- is the final relocatable cross-compiler for the SDK, in this case for the ARM architecture.
gcc-crosssdk is an intermediate step in producing gcc-cross-canadian.
the *-initial are the initial versions of the compiler required to bootstrap the toolchain separately for the standard cross-compiler and for the SDK.
gcc-runtime builds the runtime components that come as part of gcc (e.g. libstdc++).
gccmakedep isn't really part of gcc itself, it's a script that comes as part of the X11 utilities that some projects need to determine dependencies for each source file.
When you say "you only need to build gcc", it's not entirely clear what you mean, but I suspect it's either gcc for the target (in which case it's "gcc", though I suspect you'll probably need more than that - packagegroup-core-buildessential may be what you want) or you want a cross-compiler you can install separately in which case you probably ought to bitbake meta-toolchain or bitbake -c populate_sdk imagename. That'll contain more than just gcc but it's likely gcc alone isn't going to be enough anyway.

Answer 2

GCC is a huge project. Maybe this recipe could help you understand GCC and Yocto a little bit better. The following information is some information paraphrase from "Embedded Linux Projects Using Yocto Project Cookbook" by Alex Gonzalez
GNU toolchain contains the following components:
Assembler (GNU as): part of the binutils package
Linker (GNU Id):
part of the binutils package
Compiler (GNU gcc): support for C, C++,
Java, Ada, Fortran, and Objective C
Debugger (GNU gdb): GNU debugger
Binary file tools (objdump, nm, objcopy, readelf, strip, and so on):
these are part of the binutils package
These components are enough to build bare metal applications
bootloaders like u-boot, Linux Kernel because they do not need C
library and they implement C library functions they need.
POSIX-compliant C library is needed for LInux user space applications.
glibc is the default C library used in the Yocto Project.
On Embedded Systems, we need a cross-compilation toolchain. We build
in a host computer but run the result binarines on the target which is
usually different architecture. There are several types of toolchains
based on build machine, target machine.
The most common combinations are:
Native: An example of this is an x86 machine running a toolchain that >has also been built on an x86 machine
producing binaries to run on an x86 machine. This is common in desktop
computers.
Cross-compilation: This is the most common on embedded
systems; for example, an x86 machine running a toolchain that has also
been built on an x86 machine but producing binaries to run on a
different architecture, like ARM.
Cross-native: This is typically the
toolchain running on targets. An example of this is where a toolchain
has been built on an x86 machine but runs on ARM and produces
Canadian: Rarely seen, this is where the build, host, and target
machines are all different.