linux-kernel - RE: [PATCH] Raise the minimum GCC version to 5.2

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Date:   Mon, 3 May 2021 12:20:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arnd Bergmann' <arnd@...db.de>,
        Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Joe Perches <joe@...ches.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        "Linux Doc Mailing List" <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] Raise the minimum GCC version to 5.2

From: Arnd Bergmann
> Sent: 03 May 2021 10:25
...
> One scenario that I've seen previously is where user space and
> kernel are built together as a source based distribution (OE, buildroot,
> openwrt, ...), and the compiler is picked to match the original sources
> of the user space because that is best tested, but the same compiler
> then gets used to build the kernel as well because that is the default
> in the build environment.

If you are building programs for release to customers who might
be running then on old distributions then you need a system with
the original userspace headers and almost certainly a similar
vintage compiler.
Never mind RHEL7 we have customers running RHEL6.
(We've managed to get everyone off RHEL5.)
So the build machine is running a 10+ year old distro.

I did try to build on a newer system (only 5 years old)
but the complete fubar of memcpy() makes it impossible
to compile C programs that will run on an older libc.
And don't even mention C++, the 'character traits' is just
plain horrid - enough to make me want to remove every
reference to CString from the small amount of C++ we have.

To quote our makefile:
# C++ is fighting back.
# I'd like to be able to compile on a 'new' system and still be able to run
# the binaries on RHEL 6 (2.6.32 kernel 2011 era libraries).
# But even linking libstdc++ static still leaves
# an undefined C++ symbol that the dynamic loader barfs on.
# The static libstdc++ also references memcpy@...BC_2.14 - but that can be
# 'solved' by adding an extra .so that defines the symbol (and calls memmove()).
# I've also tried pulling a single .o out of libstc++.a. This might work if
# the .o is small and self contained.
#
# For now we statically link libstc++ and continue to build on an old system.
C++LDLIBS := -Wl,-Bstatic -lstdc++ -Wl,-Bdynamic

It would be nice to be able to build current kernels (for local
use) on the 'new' system - but gcc is already too old.

	David

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