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Re: [PATCH] jump label: fix passing kbuild_cflags when checking for asm goto support

From Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Newsgroups linux.kernel
Subject Re: [PATCH] jump label: fix passing kbuild_cflags when checking for asm goto support
Date 2017-03-10 18:50 +0100
Message-ID <tjwPT-7iA-3@gated-at.bofh.it> (permalink)
References <tjvAt-6xJ-3@gated-at.bofh.it> <tjwdb-72n-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Fri, Mar 10, 2017 at 12:04:22PM -0500, Steven Rostedt wrote:
> On Fri, 10 Mar 2017 19:24:18 +0300
> Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org> wrote:
> 
> > The latest change of asm goto support check added passing of
> > KBUILD_CFLAGS to compiler.  When these flags reference gcc plugins,
> > there is a race condition between the build of these plugins and their
> > use in this asm goto support check.
> > 
> > This change moves the check before all these references are added
> > to KBUILD_CFLAGS.  This is correct because subsequent KBUILD_CFLAGS
> > modifications are not relevant to this check.
> 
> What exactly breaks when the race happens?

Actually, this is not quite a race.  When you run "make bzImage" followed
by "make modules", the kernel is always built with HAVE_JUMP_LABEL
disabled, while the modules are built depending on CONFIG_JUMP_LABEL.
If HAVE_JUMP_LABEL macro happens to be different, modules are built
with undefined references:

ERROR: "static_key_slow_inc" [net/netfilter/xt_TEE.ko] undefined!
ERROR: "static_key_slow_dec" [net/netfilter/xt_TEE.ko] undefined!
ERROR: "static_key_slow_dec" [net/netfilter/nft_meta.ko] undefined!
ERROR: "static_key_slow_inc" [net/netfilter/nft_meta.ko] undefined!
ERROR: "nf_hooks_needed" [net/netfilter/ipvs/ip_vs.ko] undefined!
ERROR: "nf_hooks_needed" [net/ipv6/ipv6.ko] undefined!
ERROR: "static_key_count" [net/ipv6/ipv6.ko] undefined!
ERROR: "static_key_slow_inc" [net/ipv6/ipv6.ko] undefined!
ERROR: "nf_hooks_needed" [net/decnet/decnet.ko] undefined!

-- 
glebfm

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[PATCH] jump label: fix passing kbuild_cflags when checking for asm  goto support Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org> - 2017-03-10 17:30 +0100
  Re: [PATCH] jump label: fix passing kbuild_cflags when checking for  asm goto support Steven Rostedt <rostedt@goodmis.org> - 2017-03-10 18:10 +0100
    Re: [PATCH] jump label: fix passing kbuild_cflags when checking for  asm goto support Steven Rostedt <rostedt@goodmis.org> - 2017-03-10 18:50 +0100
      [PATCH v2] jump label: fix passing kbuild_cflags when checking for  asm goto support Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org> - 2017-03-10 19:00 +0100
        Re: [PATCH v2] jump label: fix passing kbuild_cflags when checking  for asm goto support Steven Rostedt <rostedt@goodmis.org> - 2017-03-10 19:10 +0100
        Re: [PATCH v2] jump label: fix passing kbuild_cflags when checking  for asm goto support David Lin <dtwlin@google.com> - 2017-03-10 19:40 +0100
    Re: [PATCH] jump label: fix passing kbuild_cflags when checking for  asm goto support Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org> - 2017-03-10 18:50 +0100

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