Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section

[Arnd Bergmann]

On Tue, Mar 16, 2021 at 5:27 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> On Tue, Mar 16, 2021 at 10:45:32AM +0000, Catalin Marinas wrote:
> > On Fri, Feb 26, 2021 at 08:32:57PM -0800, Fangrui Song wrote:
> > > On 2021-02-26, Kees Cook wrote:
> > > > On Fri, Feb 26, 2021 at 03:03:39PM +0100, Arnd Bergmann wrote:
> > > > > From: Arnd Bergmann <arnd@xxxxxxxx>
> > > > >
> > > > > When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION,
> > > > > I sometimes see an assertion
> > > > >
> > > > >  ld.lld: error: Entry trampoline text too big
> > > >
> > > > Heh, "too big" seems a weird report for having it discarded. :)
> > > >
> > > > Any idea on this Fangrui?
> > > >
> > > > ( I see this is https://github.com/ClangBuiltLinux/linux/issues/1311 )
> > >
> > > This diagnostic is from an ASSERT in arch/arm64/kernel/vmlinux.lds
> > >
> > >   ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == (1 << 16),
> > >    "Entry trampoline text too big")
> >
> > Can we not change the ASSERT to be <= PAGE_SIZE instead?
>
> Ah, that won't work as I suspect we still need the trampoline section.
>
> Arnd, do you know why this section disappears? I did a simple test with
> defconfig + LD_DEAD_CODE_DATA_ELIMINATION and the trampoline section is
> still around.

If I remember correctly, this showed up when CONFIG_ARM_SDE_INTERFACE
is disabled, which dropped the only reference into this section.
If that doesn't make sense, I can try digging through the old build logs to
reproduce the problem.

    Arnd