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Re: [PATCH], Add configuration checks to PowerPC --with-long-double-format=ieee
On Fri, 6 Jul 2018, Segher Boessenkool wrote:
> Version checks are terrible. This is nothing new.
The key principle behind --with-glibc-version is that you can pass that
option *when building the static-only inhibit_libc bootstrap compiler
without having built glibc yet* and it will result in the compiler being
correctly configured for the specified glibc version, and thus able to
build glibc binaries identical to those you get from a longer alternating
sequence of compiler and glibc (headers) builds.
At that point in a bootstrap of a cross toolchain you don't have any
target glibc headers available (you might have target kernel headers) and
so have no other way in which the compiler can possibly tell what glibc
version is in use.
> For cross builds you can just assume it works. That should work fine here.
We definitely support building a new GCC using a sysroot of an old glibc
(so that the new GCC can then be used to build binaries that will run on
old distributions, for example). (This certainly works and is useful for
x86_64; I don't assert whether or not it works, or makes sense, for
Of course in that case the build can examine target headers to determine
versions and features, but a new GCC release is still likely to be able to
build a few past glibc release branches if anyone backported the required
build fixes to those branches, and so the bootstrap case is still useful
with somewhat older glibc versions.
Joseph S. Myers