lkml.org 
[lkml]   [2021]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()
From
Date


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

\
 
 \ /
  Last update: 2021-03-03 15:10    [W:0.091 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site