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Date: Mon, 25 May 2015 10:56:31 -0000
Subject: Re: [PATCH] ARM: module: Add ".ref.text" to arm unwind tables
From: vigneshr@codeaurora.org
To: linux@arm.linux.org.uk, a.ryabinin@samsung.com, akpm@linux-foundation.org,
        adech.fo@gmail.com
Cc: "Laura Abbott" <labbott@redhat.com>, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
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Forgot to add Maintainers. Adding them now.

> On 05/13/2015 08:20 AM, Vignesh Radhakrishnan wrote:
>> Functions inside kernel modules that use __ref
>> will end up being placed in .ARM.exidx.ref.text
>> section by gcc.
>>
>> Currently we don't consider adding these functions
>> to arm unwind tables.
>>
>> Hence, if we turn slub debug on by default we end up
>> with the messages of this sort:
>>
>> 	unwind: Index not found bf0011e0
>>
>> This is because slub debug saves stack trace of
>> allocation's and free's. Therefore, we end up seeing
>> a flood of these messages in dmesg since its not
>> able to locate these functions.
>>
>> Fix this by adding .ref.text section to arm unwind tables.
>>
>
> With this patch, I go from
>
>   ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 63 at drivers/misc/test.c:12 that_function+0x10/0x2c
> [test]()
> Modules linked in: test(P+)
> CPU: 0 PID: 63 Comm: insmod Tainted: P                4.1.0-rc2+ #28
> Hardware name: ARM-Versatile PB
> [<c001a590>] (unwind_backtrace) from [<c0017b84>] (show_stack+0x10/0x14)
> [<c0017b84>] (show_stack) from [<c0022370>]
> (warn_slowpath_common+0x78/0xb0)
> [<c0022370>] (warn_slowpath_common) from [<c0022444>]
> (warn_slowpath_null+0x1c/0x24)
> [<c0022444>] (warn_slowpath_null) from [<bf000048>]
> (that_function+0x10/0x2c [test])
> unwind: Index not found bf000048
> ---[ end trace 3e24f8edd90f3b27 ]---
>
> to
>
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 63 at drivers/misc/test.c:12 that_function+0x10/0x2c
> [test]()
> Modules linked in: test(P+)
> CPU: 0 PID: 63 Comm: insmod Tainted: P                4.1.0-rc2+ #30
> Hardware name: ARM-Versatile PB
> [<c001a5d0>] (unwind_backtrace) from [<c0017b84>] (show_stack+0x10/0x14)
> [<c0017b84>] (show_stack) from [<c0022770>]
> (warn_slowpath_common+0x78/0xb0)
> [<c0022770>] (warn_slowpath_common) from [<c0022844>]
> (warn_slowpath_null+0x1c/0x24)
> [<c0022844>] (warn_slowpath_null) from [<bf000048>]
> (that_function+0x10/0x2c [test])
> [<bf000048>] (that_function [test]) from [<bf002010>]
> (awesome_module+0x10/0x1c [test])
> [<bf002010>] (awesome_module [test]) from [<c0009710>]
> (do_one_initcall+0x80/0x1dc)
> [<c0009710>] (do_one_initcall) from [<c02d14e0>]
> (do_init_module+0x58/0x1a8)
> [<c02d14e0>] (do_init_module) from [<c0063940>]
> (load_module+0x170c/0x1c38)
> [<c0063940>] (load_module) from [<c0063f38>] (SyS_init_module+0xcc/0x124)
> [<c0063f38>] (SyS_init_module) from [<c0014900>]
> (ret_fast_syscall+0x0/0x30)
> ---[ end trace 554c9ff461eb2505 ]---
>
> Tested-by: Laura Abbott <labbott@redhat.com>
>
>> Signed-off-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>
>> ---
>>   arch/arm/include/asm/module.h | 1 +
>>   arch/arm/kernel/module.c      | 4 ++++
>>   2 files changed, 5 insertions(+)
>>
>> diff --git a/arch/arm/include/asm/module.h
>> b/arch/arm/include/asm/module.h
>> index ed690c4..17640c9 100644
>> --- a/arch/arm/include/asm/module.h
>> +++ b/arch/arm/include/asm/module.h
>> @@ -14,6 +14,7 @@ enum {
>>   	ARM_SEC_DEVEXIT,
>>   	ARM_SEC_HOT,
>>   	ARM_SEC_UNLIKELY,
>> +	ARM_SEC_REF,
>>   	ARM_SEC_MAX,
>>   };
>>
>> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
>> index 2e11961..846b888 100644
>> --- a/arch/arm/kernel/module.c
>> +++ b/arch/arm/kernel/module.c
>> @@ -308,6 +308,8 @@ int module_finalize(const Elf32_Ehdr *hdr, const
>> Elf_Shdr *sechdrs,
>>   			maps[ARM_SEC_UNLIKELY].unw_sec = s;
>>   		else if (strcmp(".ARM.exidx.text.hot", secname) == 0)
>>   			maps[ARM_SEC_HOT].unw_sec = s;
>> +		else if (strcmp(".ARM.exidx.ref.text", secname) == 0)
>> +			maps[ARM_SEC_REF].unw_sec = s;
>>   		else if (strcmp(".init.text", secname) == 0)
>>   			maps[ARM_SEC_INIT].txt_sec = s;
>>   		else if (strcmp(".text", secname) == 0)
>> @@ -318,6 +320,8 @@ int module_finalize(const Elf32_Ehdr *hdr, const
>> Elf_Shdr *sechdrs,
>>   			maps[ARM_SEC_UNLIKELY].txt_sec = s;
>>   		else if (strcmp(".text.hot", secname) == 0)
>>   			maps[ARM_SEC_HOT].txt_sec = s;
>> +		else if (strcmp(".ref.text", secname) == 0)
>> +			maps[ARM_SEC_REF].txt_sec = s;
>>   	}
>>
>>   	for (i = 0; i < ARM_SEC_MAX; i++)
>>
>
>

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of the Code Aurora Forum, hosted by The Linux Foundation.
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