linux-kernel - Re: Problems with commit 'kallsyms: add support for relative offsets in kallsyms address table' (in mmotm)

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Date:	Sat, 23 Jan 2016 18:35:46 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Problems with commit 'kallsyms: add support for relative offsets
 in kallsyms address table' (in mmotm)

On 01/23/2016 06:06 PM, Guenter Roeck wrote:
> Hi,
>
> I see runtime problems with the current mmotm branch. All qemu mips targets
> (32 and 64 bit, big and little endian) are stuck in boot after this commit.
>
> Bisect points to commit d13682e4d9d2 ("kallsyms: add support for relative offsets
> in kallsyms address table". Disabling CONFIG_KALLSYMS_BASE_RELATIVE fixes the problem,
> ie I can boot the image with qemu.
>
> Bisect log is attached.
>
> Playing with the problem, I found the following:
>
> 1) The problem is only seen with a toolchain using binutils 2.22, but not
>     with a toolchain using binutils 2.25. The compiler configuration may be
>     different for both toolchains.
> 2) Message "kallsyms failure: absolute symbol value 0xffffffff807afd14 out of range
>     in relative mode" (twice) when using the toolchain with binutils 2.22.
>     This does not cause the build to fail, though.
> 3) kallsyms_sym_address() parameter variable type is "int". In the calling code,
>     the variable type used is "unsigned long". That has no impact on the problem,
>     though.
>

An additional data point: When using the older toolchain, many symbols in System.map
are marked "A".
	ffffffff80100000 A _text
With the more recent toolchain, the same symbols are marked "T".
	ffffffff80100000 T _text

Guenter

> Please let me know if there is anything I can do to help tracking down the problem.
>
> Thanks,
> Guenter
>
> ---
> # bad: [437b7ef6d6484bb36afb2c75897e14bf03113dbd] pci: test for unexpectedly disabled bridges
> # good: [afd2ff9b7e1b367172f18ba7f693dfb62bdcb2dc] Linux 4.4
> git bisect start 'HEAD' 'v4.4'
> # bad: [10078c1820d81131bc338c7c919feb2638a912ad] ocfs2: o2hb: add NEGOTIATE_APPROVE message
> git bisect bad 10078c1820d81131bc338c7c919feb2638a912ad
> # bad: [1b06048b37e888edb609e1509070ec0c6580eedd] kallsyms-add-support-for-relative-offsets-in-kallsyms-address-table-fix
> git bisect bad 1b06048b37e888edb609e1509070ec0c6580eedd
> # good: [ed312d94332968c86f53295795a3d122fd32cea2] arch/alpha/kernel/systbls.S: remove debug check
> git bisect good ed312d94332968c86f53295795a3d122fd32cea2
> # good: [1cbe7000217b0126821ecd8fba0ba5f9315a0560] thp: limit number of object to scan on deferred_split_scan()
> git bisect good 1cbe7000217b0126821ecd8fba0ba5f9315a0560
> # good: [474324b13e8184aa088c722b771f0f31ab773476] vmstat: remove BUG_ON from vmstat_update
> git bisect good 474324b13e8184aa088c722b771f0f31ab773476
> # good: [d94a9840c248207040d62ca0f380943db9423418] proc: fix missing reference of mm
> git bisect good d94a9840c248207040d62ca0f380943db9423418
> # bad: [d13682e4d9d2ad8220354b5e1a2bd6623e1f2e38] kallsyms: add support for relative offsets in kallsyms address table
> git bisect bad d13682e4d9d2ad8220354b5e1a2bd6623e1f2e38
> # first bad commit: [d13682e4d9d2ad8220354b5e1a2bd6623e1f2e38] kallsyms: add support for relative offsets in kallsyms address table