Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Steven Rostedt]

This requires an acked-by from one of the ARM64 maintainers.

-- Steve


On Thu, 25 Feb 2021 22:07:47 +0800
Li Huafei <lihuafei1@huawei.com> wrote:

> When cross-compiling the kernel, the endian of the target machine and
> the local machine may not match, at this time the recordmcount tool
> needs byte reversal when processing elf's variables to get the correct
> value. w* callback function is used to solve this problem, w is used for
> 4-byte variable processing, while w8 is used for 8-byte.
> 
> arm64_is_fake_mcount() is used to filter '_mcount' relocations that are
> not used by ftrace. In arm64_is_fake_mcount(), rp->info is 8 bytes in
> size, but w is used. This causes arm64_is_fake_mcount() to get the wrong
> type of relocation when we cross-compile the arm64_be kernel image on an
> x86_le machine, and all valid '_mcount' is filtered out. The
> recordmcount tool does not collect any mcount function call locations.
> At kernel startup, the following ftrace log is seen:
> 
> 	ftrace: No functions to be traced?
> 
> and thus ftrace cannot be used.
> 
> Using w8 to get the value of rp->r_info will fix the problem.
> 
> Fixes: ea0eada45632 ("recordmcount: only record relocation of type
> R_AARCH64_CALL26 on arm64")
> Signed-off-by: Li Huafei <lihuafei1@huawei.com>
> ---
>  scripts/recordmcount.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index b9c2ee7ab43f..cce12e1971d8 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
>  
>  static int arm64_is_fake_mcount(Elf64_Rel const *rp)
>  {
> -	return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> +	return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;
>  }
>  
>  /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.


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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Will Deacon]

On Thu, Feb 25, 2021 at 09:44:26AM -0500, Steven Rostedt wrote:
> This requires an acked-by from one of the ARM64 maintainers.
> 
> -- Steve
> 
> 
> On Thu, 25 Feb 2021 22:07:47 +0800
> Li Huafei <lihuafei1@huawei.com> wrote:
> 
> > When cross-compiling the kernel, the endian of the target machine and
> > the local machine may not match, at this time the recordmcount tool
> > needs byte reversal when processing elf's variables to get the correct
> > value. w* callback function is used to solve this problem, w is used for
> > 4-byte variable processing, while w8 is used for 8-byte.
> > 
> > arm64_is_fake_mcount() is used to filter '_mcount' relocations that are
> > not used by ftrace. In arm64_is_fake_mcount(), rp->info is 8 bytes in
> > size, but w is used. This causes arm64_is_fake_mcount() to get the wrong
> > type of relocation when we cross-compile the arm64_be kernel image on an
> > x86_le machine, and all valid '_mcount' is filtered out. The
> > recordmcount tool does not collect any mcount function call locations.
> > At kernel startup, the following ftrace log is seen:
> > 
> > 	ftrace: No functions to be traced?
> > 
> > and thus ftrace cannot be used.
> > 
> > Using w8 to get the value of rp->r_info will fix the problem.
> > 
> > Fixes: ea0eada45632 ("recordmcount: only record relocation of type
> > R_AARCH64_CALL26 on arm64")
> > Signed-off-by: Li Huafei <lihuafei1@huawei.com>
> > ---
> >  scripts/recordmcount.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> > index b9c2ee7ab43f..cce12e1971d8 100644
> > --- a/scripts/recordmcount.c
> > +++ b/scripts/recordmcount.c
> > @@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> >  
> >  static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> >  {
> > -	return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> > +	return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;

Acked-by: Will Deacon <will@kernel.org>

But you know you could avoid these sorts of problems by moving to little
endian along with everybody else? ;)

Will

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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Steven Rostedt]

On Thu, 25 Feb 2021 16:01:17 +0000
Will Deacon <will@kernel.org> wrote:

> Acked-by: Will Deacon <will@kernel.org>

Thanks!

> 
> But you know you could avoid these sorts of problems by moving to little
> endian along with everybody else? ;)

But then how do we find these bug?

-- Steve

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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Steven Rostedt]

On Thu, 25 Feb 2021 16:01:17 +0000
Will Deacon <will@kernel.org> wrote:

> On Thu, Feb 25, 2021 at 09:44:26AM -0500, Steven Rostedt wrote:
> > This requires an acked-by from one of the ARM64 maintainers.
> > 
> > -- Steve
> > 
> > 
> > On Thu, 25 Feb 2021 22:07:47 +0800
> > Li Huafei <lihuafei1@huawei.com> wrote:
> >   
> > > When cross-compiling the kernel, the endian of the target machine and
> > > the local machine may not match, at this time the recordmcount tool
> > > needs byte reversal when processing elf's variables to get the correct
> > > value. w* callback function is used to solve this problem, w is used for
> > > 4-byte variable processing, while w8 is used for 8-byte.
> > > 
> > > arm64_is_fake_mcount() is used to filter '_mcount' relocations that are
> > > not used by ftrace. In arm64_is_fake_mcount(), rp->info is 8 bytes in
> > > size, but w is used. This causes arm64_is_fake_mcount() to get the wrong
> > > type of relocation when we cross-compile the arm64_be kernel image on an
> > > x86_le machine, and all valid '_mcount' is filtered out. The
> > > recordmcount tool does not collect any mcount function call locations.
> > > At kernel startup, the following ftrace log is seen:
> > > 
> > > 	ftrace: No functions to be traced?
> > > 
> > > and thus ftrace cannot be used.
> > > 
> > > Using w8 to get the value of rp->r_info will fix the problem.
> > > 
> > > Fixes: ea0eada45632 ("recordmcount: only record relocation of type
> > > R_AARCH64_CALL26 on arm64")
> > > Signed-off-by: Li Huafei <lihuafei1@huawei.com>
> > > ---
> > >  scripts/recordmcount.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> > > index b9c2ee7ab43f..cce12e1971d8 100644
> > > --- a/scripts/recordmcount.c
> > > +++ b/scripts/recordmcount.c
> > > @@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> > >  
> > >  static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> > >  {
> > > -	return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> > > +	return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;  
> 
> Acked-by: Will Deacon <will@kernel.org>
> 
> But you know you could avoid these sorts of problems by moving to little
> endian along with everybody else? ;)
> 

I just realized that I received this patch twice, and thought it was the
same patch! Chen was three days ahead of you, so he get's the credit ;-)

 https://lore.kernel.org/r/20210222135840.56250-1-chenjun102@huawei.com

-- Steve

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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Steven Rostedt]

On Tue, 2 Mar 2021 17:30:58 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> I just realized that I received this patch twice, and thought it was the
> same patch! Chen was three days ahead of you, so he get's the credit ;-)
> 
>  https://lore.kernel.org/r/20210222135840.56250-1-chenjun102@huawei.com

I'm applying this patch (same one here but came earlier).

Will, you still OK with your acked-by on it?

-- Steve

From 999340d51174ce4141dd723105d4cef872b13ee9 Mon Sep 17 00:00:00 2001
From: Chen Jun <chenjun102@huawei.com>
Date: Mon, 22 Feb 2021 13:58:40 +0000
Subject: [PATCH] ftrace: Have recordmcount use w8 to read relp->r_info in
 arm64_is_fake_mcount

On little endian system, Use aarch64_be(gcc v7.3) downloaded from
linaro.org to build image with CONFIG_CPU_BIG_ENDIAN = y,
CONFIG_FTRACE = y, CONFIG_DYNAMIC_FTRACE = y.

gcc will create symbols of _mcount but recordmcount can not create
mcount_loc for *.o.
aarch64_be-linux-gnu-objdump -r fs/namei.o | grep mcount
00000000000000d0 R_AARCH64_CALL26  _mcount
...
0000000000007190 R_AARCH64_CALL26  _mcount

The reason is than funciton arm64_is_fake_mcount can not work correctly.
A symbol of _mcount in *.o compiled with big endian compiler likes:
00 00 00 2d 00 00 01 1b
w(rp->r_info) will return 0x2d instead of 0x011b. Because w() takes
uint32_t as parameter, which truncates rp->r_info.

Use w8() instead w() to read relp->r_info

Link: https://lkml.kernel.org/r/20210222135840.56250-1-chenjun102@huawei.com

Fixes: ea0eada45632 ("recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.")
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 scripts/recordmcount.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index b9c2ee7ab43f..cce12e1971d8 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
 
 static int arm64_is_fake_mcount(Elf64_Rel const *rp)
 {
-	return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
+	return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;
 }
 
 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
-- 
2.25.4


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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Will Deacon]

On Tue, Mar 02, 2021 at 05:33:35PM -0500, Steven Rostedt wrote:
> On Tue, 2 Mar 2021 17:30:58 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > I just realized that I received this patch twice, and thought it was the
> > same patch! Chen was three days ahead of you, so he get's the credit ;-)
> > 
> >  https://lore.kernel.org/r/20210222135840.56250-1-chenjun102@huawei.com
> 
> I'm applying this patch (same one here but came earlier).
> 
> Will, you still OK with your acked-by on it?

Absolutely!

Will

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Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()

[Li Huafei]

On 2021/3/3 6:30, Steven Rostedt wrote:
> On Thu, 25 Feb 2021 16:01:17 +0000
> Will Deacon <will@kernel.org> wrote:
> 
>> On Thu, Feb 25, 2021 at 09:44:26AM -0500, Steven Rostedt wrote:
>>> This requires an acked-by from one of the ARM64 maintainers.
>>>
>>> -- Steve
>>>
>>>
>>> On Thu, 25 Feb 2021 22:07:47 +0800
>>> Li Huafei <lihuafei1@huawei.com> wrote:
>>>    
>>>> When cross-compiling the kernel, the endian of the target machine and
>>>> the local machine may not match, at this time the recordmcount tool
>>>> needs byte reversal when processing elf's variables to get the correct
>>>> value. w* callback function is used to solve this problem, w is used for
>>>> 4-byte variable processing, while w8 is used for 8-byte.
>>>>
>>>> arm64_is_fake_mcount() is used to filter '_mcount' relocations that are
>>>> not used by ftrace. In arm64_is_fake_mcount(), rp->info is 8 bytes in
>>>> size, but w is used. This causes arm64_is_fake_mcount() to get the wrong
>>>> type of relocation when we cross-compile the arm64_be kernel image on an
>>>> x86_le machine, and all valid '_mcount' is filtered out. The
>>>> recordmcount tool does not collect any mcount function call locations.
>>>> At kernel startup, the following ftrace log is seen:
>>>>
>>>> 	ftrace: No functions to be traced?
>>>>
>>>> and thus ftrace cannot be used.
>>>>
>>>> Using w8 to get the value of rp->r_info will fix the problem.
>>>>
>>>> Fixes: ea0eada45632 ("recordmcount: only record relocation of type
>>>> R_AARCH64_CALL26 on arm64")
>>>> Signed-off-by: Li Huafei <lihuafei1@huawei.com>
>>>> ---
>>>>   scripts/recordmcount.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
>>>> index b9c2ee7ab43f..cce12e1971d8 100644
>>>> --- a/scripts/recordmcount.c
>>>> +++ b/scripts/recordmcount.c
>>>> @@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
>>>>   
>>>>   static int arm64_is_fake_mcount(Elf64_Rel const *rp)
>>>>   {
>>>> -	return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
>>>> +	return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;
>>
>> Acked-by: Will Deacon <will@kernel.org>
>>
>> But you know you could avoid these sorts of problems by moving to little
>> endian along with everybody else? ;)
>>
> 
> I just realized that I received this patch twice, and thought it was the
> same patch! Chen was three days ahead of you, so he get's the credit ;-)
> 
>   https://lore.kernel.org/r/20210222135840.56250-1-chenjun102@huawei.com
> 
> -- Steve
> .
> 

That's fine, thanks Steve and Will!

Huafei

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