Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake_mcount()
From: Will Deacon
Date: Thu Feb 25 2021 - 11:02:16 EST
On Thu, Feb 25, 2021 at 09:44:26AM -0500, Steven Rostedt wrote:
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This requires an acked-by from one of the ARM64 maintainers.
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-- Steve
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On 2021年2月25日 22:07:47 +0800
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Li Huafei <lihuafei1@xxxxxxxxxx> wrote:
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> When cross-compiling the kernel, the endian of the target machine and
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> the local machine may not match, at this time the recordmcount tool
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> needs byte reversal when processing elf's variables to get the correct
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> value. w* callback function is used to solve this problem, w is used for
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> 4-byte variable processing, while w8 is used for 8-byte.
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> arm64_is_fake_mcount() is used to filter '_mcount' relocations that are
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> not used by ftrace. In arm64_is_fake_mcount(), rp->info is 8 bytes in
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> size, but w is used. This causes arm64_is_fake_mcount() to get the wrong
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> type of relocation when we cross-compile the arm64_be kernel image on an
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> x86_le machine, and all valid '_mcount' is filtered out. The
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> recordmcount tool does not collect any mcount function call locations.
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> At kernel startup, the following ftrace log is seen:
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> ftrace: No functions to be traced?
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> and thus ftrace cannot be used.
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> Using w8 to get the value of rp->r_info will fix the problem.
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> Fixes: ea0eada45632 ("recordmcount: only record relocation of type
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> R_AARCH64_CALL26 on arm64")
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> Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
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> ---
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> scripts/recordmcount.c | 2 +-
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> 1 file changed, 1 insertion(+), 1 deletion(-)
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> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
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> index b9c2ee7ab43f..cce12e1971d8 100644
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> --- a/scripts/recordmcount.c
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> +++ b/scripts/recordmcount.c
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> @@ -438,7 +438,7 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
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> static int arm64_is_fake_mcount(Elf64_Rel const *rp)
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> {
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> - return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
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> + return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;
Acked-by: Will Deacon <will@xxxxxxxxxx>
But you know you could avoid these sorts of problems by moving to little
endian along with everybody else? ;)
Will