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

---
 scripts/recordmcount.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index b9c2ee7ab43f..cce12e1971d8 100644
@@ -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.

2.25.0

Hi

There is no problem when I use aarch64_be(gcc v10.2). Because gcc v10.2 use __patchable_function_entries instead of __mcount. I am not sure when the change happened.

Regards,
Chen Jun

-----邮件原件-----
发件人: Chen Jun [mailto:[email protected]]
发送时间: 2021年2月22日 21:59
收件人: [email protected]
抄送: [email protected]; [email protected]; [email protected]; Xiangrui (Euler) <[email protected]> 主题: [PATCH] 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

---
 scripts/recordmcount.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -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.
--

2.25.0

But you are still saying that this patch needs to be applied, right?

-- Steve

Yes，this patch needs to be applied.

Regards
Chen Jun