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>
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