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    SubjectRe: [PATCH v3 1/2] x86/mm: Identify the end of the kernel area to be reserved
    On Tue, Jul 23, 2019 at 03:05:14PM +0200, Greg KH wrote:
    > On Mon, Jul 15, 2019 at 01:16:48PM -0700, H.J. Lu wrote:
    > > On Mon, Jul 15, 2019 at 3:35 AM Thomas Gleixner <tglx@linutronix.de> wrote:
    > > >
    > > > On Mon, 15 Jul 2019, Thomas Gleixner wrote:
    > > > > On Mon, 15 Jul 2019, Mike Lothian wrote:
    > > > > > That build failure is from the current tip of Linus's tree
    > > > > > If the fix is in, then it hasn't fixed the issue
    > > > >
    > > > > The reverted commit caused a build fail with gold as well. Let me stare at
    > > > > your issue.
    > > >
    > > > So with gold the build fails in the reloc tool complaining about that
    > > > relocation:
    > > >
    > > > Invalid absolute R_X86_64_32S relocation: __end_of_kernel_reserve
    > > >
    > > > The commit does:
    > > >
    > > > +extern char __end_of_kernel_reserve[];
    > > > +
    > > >
    > > > void __init setup_arch(char **cmdline_p)
    > > > {
    > > > + /*
    > > > + * Reserve the memory occupied by the kernel between _text and
    > > > + * __end_of_kernel_reserve symbols. Any kernel sections after the
    > > > + * __end_of_kernel_reserve symbol must be explicitly reserved with a
    > > > + * separate memblock_reserve() or they will be discarded.
    > > > + */
    > > > memblock_reserve(__pa_symbol(_text),
    > > > - (unsigned long)__bss_stop - (unsigned long)_text);
    > > > + (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
    > > >
    > > > So it replaces __bss_stop with __end_of_kernel_reserve here.
    > > >
    > > > --- a/arch/x86/kernel/vmlinux.lds.S
    > > > +++ b/arch/x86/kernel/vmlinux.lds.S
    > > > @@ -368,6 +368,14 @@ SECTIONS
    > > > __bss_stop = .;
    > > > }
    > > >
    > > > + /*
    > > > + * The memory occupied from _text to here, __end_of_kernel_reserve, is
    > > > + * automatically reserved in setup_arch(). Anything after here must be
    > > > + * explicitly reserved using memblock_reserve() or it will be discarded
    > > > + * and treated as available memory.
    > > > + */
    > > > + __end_of_kernel_reserve = .;
    > > >
    > > > And from the linker script __bss_stop and __end_of_kernel_reserve are
    > > > exactly the same. From System.map (of a successful ld build):
    > > >
    > > > ffffffff82c00000 B __brk_base
    > > > ffffffff82c00000 B __bss_stop
    > > > ffffffff82c00000 B __end_bss_decrypted
    > > > ffffffff82c00000 B __end_of_kernel_reserve
    > > > ffffffff82c00000 B __start_bss_decrypted
    > > > ffffffff82c00000 B __start_bss_decrypted_unused
    > > >
    > > > So how on earth can gold fail with that __end_of_kernel_reserve change?
    > > >
    > > > For some unknown reason it turns that relocation into an absolute
    > > > one. That's clearly a gold bug^Wfeature and TBH, I'm more than concerned
    > > > about that kind of behaviour.
    > > >
    > > > If we just revert that commit, then what do we achieve? We paper over the
    > > > underlying problem, which is not really helping anything.
    > > >
    > > > Aside of that gold still fails to build the X32 VDSO and it does so for a
    > > > very long time....
    > > >
    > > > Until we really understand what the problem is, this stays as is.
    > > >
    > > > @H.J.: Any insight on that?
    > > >
    > >
    > > Since building a workable kernel for different kernel configurations isn't a
    > > requirement for gold, I don't recommend gold for kernel.
    >
    > Um, it worked before this commit, and now it doesn't. "Some" companies
    > are using gold for linking the kernel today...

    Oh nevermind, I see the rest of the thread where it's now not being
    allowed, sorry for the noise.

    greg k-h

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