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From: Arnd Bergmann <arnd@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fangrui Song <maskray@google.com>,
	Kees Cook <keescook@chromium.org>, Will Deacon <will@kernel.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	David Brazdil <dbrazdil@google.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section
Date: Tue, 16 Mar 2021 17:39:27 +0100	[thread overview]
Message-ID: <CAK8P3a07nPbbP095LJ84Z5hP3Ce53fb_+0Zav8PUA+7R_92gMw@mail.gmail.com> (raw)
In-Reply-To: <20210316162745.GA20565@arm.com>

On Tue, Mar 16, 2021 at 5:27 PM Catalin Marinas <catalin.marinas@arm.com> 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@arndb.de>
> > > > >
> > > > > 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

WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fangrui Song <maskray@google.com>,
	Kees Cook <keescook@chromium.org>,  Will Deacon <will@kernel.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	 Marc Zyngier <maz@kernel.org>,
	David Brazdil <dbrazdil@google.com>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section
Date: Tue, 16 Mar 2021 17:39:27 +0100	[thread overview]
Message-ID: <CAK8P3a07nPbbP095LJ84Z5hP3Ce53fb_+0Zav8PUA+7R_92gMw@mail.gmail.com> (raw)
In-Reply-To: <20210316162745.GA20565@arm.com>

On Tue, Mar 16, 2021 at 5:27 PM Catalin Marinas <catalin.marinas@arm.com> 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@arndb.de>
> > > > >
> > > > > 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

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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-03-16 16:40 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-26 14:03 [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section Arnd Bergmann
2021-02-26 14:03 ` Arnd Bergmann
2021-02-26 20:59 ` Kees Cook
2021-02-26 20:59   ` Kees Cook
2021-02-27  4:32   ` Fangrui Song
2021-02-27  4:32     ` Fangrui Song
2021-03-16 10:45     ` Catalin Marinas
2021-03-16 10:45       ` Catalin Marinas
2021-03-16 16:27       ` Catalin Marinas
2021-03-16 16:27         ` Catalin Marinas
2021-03-16 16:39         ` Arnd Bergmann [this message]
2021-03-16 16:39           ` Arnd Bergmann
2021-03-16 19:09           ` Catalin Marinas
2021-03-16 19:09             ` Catalin Marinas
2021-06-02 19:32             ` Kees Cook
2021-06-02 19:32               ` Kees Cook
2021-06-03 12:07               ` Catalin Marinas
2021-06-03 12:07                 ` Catalin Marinas

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