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https://gitlab.com/buildroot.org/buildroot.git
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6063a8fbcf
Currently, the internal toolchain backend does a three stage gcc
build, with the following sequence of builds:
- build gcc-initial
- configure libc, install headers and start files
- build gcc-intermediate
- build libc
- build gcc-final
However, it turns out that this is not necessary, and only a two stage
gcc build is needed. At some point, it was believed that a three stage
gcc build was needed for NPTL based toolchains with old gcc versions,
but even a gcc 4.4 build with a NPTL toolchain works fine.
So, this commit switches the internal toolchain backend to use a two
stage gcc build: just gcc-initial and gcc-final. It does so by:
* Removing the custom dependency of all C libraries build step to
host-gcc-intermediate. Now the C library packages simply have to
depend on host-gcc-initial as a normal dependency (which they
already do), and that's it.
* Build and install both gcc *and* libgcc in
host-gcc-initial. Previously, only gcc was built and installed in
host-gcc-initial. libgcc was only done in host-gcc-intermediate,
but now we need libgcc to build the C library.
* Pass appropriate environment variables to get SSP (Stack Smashing
Protection) to work properly:
- Tell the compiler that the libc will provide the SSP support, by
passing gcc_cv_libc_provides_ssp=yes. In Buildroot, we have
chosen to use the SSP support from the C library instead of the
SSP support from the compiler (this is not changed by this patch
series, it was already the case).
- Tell glibc to *not* build its own programs with SSP support. The
issue is that if glibc detects that the compiler supports
-fstack-protector, then glibc uses it to build a few things with
SSP. However, at this point, the support is not complete (we
only have host-gcc-initial, and the C library is not completely
built). So, we pass libc_cv_ssp=no to tell the C library to not
use SSP support itself. Note that this is not a big loss: only a
few parts of the C library were built with -fstack-protector,
not the entire library.
* A special change is needed for ARC, because its libgcc depends on
the C library, which breaks building libgcc in
host-gcc-initial. This looks like a bug in the ARC compiler, as it
does not obey the inhibit_libc variable which tells the compiler
build process to *not* enable things that depend on the C
library. So for now, in host-gcc-initial, we simply disable the
build of libgmon.a for ARC. It's going to be built as part of
host-gcc-final, so the final compiler will have gmon support.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
To build and use the buildroot stuff, do the following:
1) run 'make menuconfig'
2) select the packages you wish to compile
3) run 'make'
4) wait while it compiles
5) Use your shiny new root filesystem. Depending on which sort of
root filesystem you selected, you may want to loop mount it,
chroot into it, nfs mount it on your target device, burn it
to flash, or whatever is appropriate for your target system.
You do not need to be root to build or run buildroot. Have fun!
Offline build:
==============
In order to do an offline-build (not connected to the net), fetch all
selected source by issuing a
$ make source
before you disconnect.
If your build-host is never connected, then you have to copy buildroot
and your toplevel .config to a machine that has an internet-connection
and issue "make source" there, then copy the content of your dl/ dir to
the build-host.
Building out-of-tree:
=====================
Buildroot supports building out of tree with a syntax similar
to the Linux kernel. To use it, add O=<directory> to the
make command line, E.G.:
$ make O=/tmp/build
And all the output files (including .config) will be located under /tmp/build.
More finegrained configuration:
===============================
You can specify a config-file for uClibc:
$ make UCLIBC_CONFIG_FILE=/my/uClibc.config
And you can specify a config-file for busybox:
$ make BUSYBOX_CONFIG_FILE=/my/busybox.config
To use a non-standard host-compiler (if you do not have 'gcc'),
make sure that the compiler is in your PATH and that the library paths are
setup properly, if your compiler is built dynamically:
$ make HOSTCC=gcc-4.3.orig HOSTCXX=gcc-4.3-mine
Depending on your configuration, there are some targets you can use to
use menuconfig of certain packages. This includes:
$ make HOSTCC=gcc-4.3 linux-menuconfig
$ make HOSTCC=gcc-4.3 uclibc-menuconfig
$ make HOSTCC=gcc-4.3 busybox-menuconfig
Please feed suggestions, bug reports, insults, and bribes back to the
buildroot mailing list: buildroot@buildroot.org