linux-kernel - Re: [PATCH] recordmcount: Fix the wrong use of w* in arm64_is_fake

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Date:   Tue, 2 Mar 2021 17:33:35 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Will Deacon <will@...nel.org>
Cc:     Li Huafei <lihuafei1@...wei.com>, gregory.herrero@...cle.com,
        catalin.marinas@....com, christophe.leroy@...roup.eu,
        linux-kernel@...r.kernel.org, zhangjinhao2@...wei.com,
        yangjihong1@...wei.com, xukuohai@...wei.com,
        linux-arm-kernel@...ts.infradead.org,
        Chen Jun <chenjun102@...wei.com>
Subject: Re: [PATCH] recordmcount: Fix the wrong use of w* in
 arm64_is_fake_mcount()

On Tue, 2 Mar 2021 17:30:58 -0500
Steven Rostedt <rostedt@...dmis.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@...wei.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@...nel.org>
Signed-off-by: Chen Jun <chenjun102@...wei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.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