From: Sven Schnelle <svens@linux.ibm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Yinan Liu <yinan@linux.alibaba.com>,
Steven Rostedt <rostedt@goodmis.org>,
linuxppc-dev@lists.ozlabs.org,
Sachin Sant <sachinp@linux.ibm.com>,
linux-kernel@vger.kernel.org, ardb@kernel.org,
keescook@chromium.org
Subject: Re: [powerpc] ftrace warning kernel/trace/ftrace.c:2068 with code-patching selftests
Date: Thu, 27 Jan 2022 13:04:41 +0100 [thread overview]
Message-ID: <yt9dy231gzae.fsf@linux.ibm.com> (raw)
In-Reply-To: <YfKGKWW5UfZ15kCW@FVFF77S0Q05N> (Mark Rutland's message of "Thu, 27 Jan 2022 11:46:49 +0000")
Mark Rutland <mark.rutland@arm.com> writes:
>> Isn't x86 relocatable in some configurations (e.g. for KASLR)?
>>
>> I can't see how the sort works for those cases, because the mcount_loc entries
>> are absolute, and either:
>>
>> * The sorted entries will get overwritten by the unsorted relocation entries,
>> and won't be sorted.
>>
>> * The sorted entries won't get overwritten, but then the absolute address will
>> be wrong since they hadn't been relocated.
>>
>> How does that work?
From what i've seen when looking into this ftrace sort problem x86 has a
a relocation tool, which is run before final linking: arch/x86/tools/relocs.c
This tools converts all the required relocations to three types:
- 32 bit relocations
- 64 bit relocations
- inverse 32 bit relocations
These are added to the end of the image.
The decompressor then iterates over that array, and just adds/subtracts
the KASLR offset - see arch/x86/boot/compressed/misc.c, handle_relocations()
So IMHO x86 never uses 'real' relocations during boot, and just
adds/subtracts. That's why the order stays the same, and the compile
time sort works.
/Sven
next prev parent reply other threads:[~2022-01-27 12:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-24 9:19 [powerpc] ftrace warning kernel/trace/ftrace.c:2068 with code-patching selftests Sachin Sant
[not found] ` <e9422643-a210-b77f-a037-da63a9d2e925@linux.alibaba.com>
[not found] ` <20220124114548.30241947@gandalf.local.home>
[not found] ` <0fa0daec-881a-314b-e28b-3828e80bbd90@linux.alibaba.com>
[not found] ` <YfFclROd+0/61q2d@FVFF77S0Q05N>
2022-01-27 11:46 ` Mark Rutland
2022-01-27 12:03 ` Ard Biesheuvel
2022-01-27 12:20 ` Mark Rutland
2022-01-27 12:22 ` Ard Biesheuvel
2022-01-27 12:59 ` Mark Rutland
2022-01-27 13:07 ` Ard Biesheuvel
2022-01-27 13:24 ` Mark Rutland
2022-01-27 13:59 ` Ard Biesheuvel
2022-01-27 14:54 ` Mark Rutland
2022-01-27 15:01 ` Ard Biesheuvel
2022-01-27 12:04 ` Sven Schnelle [this message]
2022-01-27 12:27 ` Mark Rutland
2022-01-27 12:46 ` Steven Rostedt
2022-01-27 13:08 ` Mark Rutland
2022-01-27 13:16 ` Sven Schnelle
2022-01-27 13:33 ` Mark Rutland
2022-01-27 13:55 ` Steven Rostedt
2022-01-27 14:56 ` Mark Rutland
2022-01-27 16:41 ` Kees Cook
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