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Date:   Mon, 21 Mar 2022 13:49:28 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH 2/3] objtool: Enable and implement 'mcount' subcommand
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        Sathvika Vasireddy <sv@linux.ibm.com>
Cc:     "aik@ozlabs.ru" <aik@ozlabs.ru>,
        "jpoimboe@redhat.com" <jpoimboe@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>
References: <20220318105140.43914-1-sv@linux.ibm.com>
        <20220318105140.43914-3-sv@linux.ibm.com>
        <8e792a9a-afb8-9b26-5e97-8f51c72c2d42@csgroup.eu>
In-Reply-To: <8e792a9a-afb8-9b26-5e97-8f51c72c2d42@csgroup.eu>
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Christophe Leroy wrote:
>=20
>=20
> Le 18/03/2022 =C3=A0 11:51, Sathvika Vasireddy a =C3=A9crit=C2=A0:
>> This patch adds 'mcount' as a subcommand to objtool, and enables
>> the same for x86. objtool is built if CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
>> is selected. Additionally, architectures can select HAVE_NOP_MCOUNT
>> if they choose to nop out mcount call sites. If that config option is
>> selected, then --mnop is passed as an option to 'objtool mcount'
>>=20
>> Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
>> ---
>>   Makefile                                |   6 ++
>>   arch/x86/Kconfig                        |   3 +-
>>   scripts/Makefile.build                  |  12 +++
>>   tools/objtool/Build                     |   2 +
>>   tools/objtool/Makefile                  |   4 +-
>>   tools/objtool/builtin-mcount.c          |  74 +++++++++++++
>>   tools/objtool/include/objtool/builtin.h |   4 +-
>>   tools/objtool/include/objtool/objtool.h |   1 +
>>   tools/objtool/mcount.c                  | 138 ++++++++++++++++++++++++
>>   tools/objtool/objtool.c                 |   1 +
>>   tools/objtool/weak.c                    |   5 +
>>   11 files changed, 247 insertions(+), 3 deletions(-)
>>   create mode 100644 tools/objtool/builtin-mcount.c
>>   create mode 100644 tools/objtool/mcount.c
>>=20
>> diff --git a/Makefile b/Makefile
>> index 55a30ca69350..316f7d08b30a 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -846,7 +846,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
>>     endif
>>   endif
>>   ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
>> + ifdef CONFIG_HAVE_NOP_MCOUNT
>>     CC_FLAGS_USING	+=3D -DCC_USING_NOP_MCOUNT
>> + endif
>>   endif
>>   ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
>>     ifdef CONFIG_HAVE_C_RECORDMCOUNT
>> @@ -1303,6 +1305,10 @@ ifdef CONFIG_STACK_VALIDATION
>>   prepare: tools/objtool
>>   endif
>>  =20
>> +ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
>> +prepare: tools/objtool
>> +endif
>=20
> I don't think that will work for powerpc.
>=20
> See arch/powerpc/Makefile
>=20
> powerpc builds the VDSO under prepare: , and powerpc has=20
> CONFIG_HAVE_GENERIC_VDSO so there are some C files in that step that=20
> seem to use objtool, allthough that looks odd to me. Must be something=20
> to fix somewhere.
>=20
>    powerpc64-linux-gcc=20
> -Wp,-MMD,arch/powerpc/kernel/vdso/.vgettimeofday-64.o.d -nostdinc=20
> -I./arch/powerpc/include -I./arch/powerpc/include/generated  -I./include=20
> -I./arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi=20
> -I./include/uapi -I./include/generated/uapi -include=20
> ./include/linux/compiler-version.h -include ./include/linux/kconfig.h=20
> -include ./include/linux/compiler_types.h -D__KERNEL__ -I ./arch/powerpc=20
> -DHAVE_AS_ATHIGH=3D1 -fmacro-prefix-map=3D./=3D -Wall -Wundef=20
> -Werror=3Dstrict-prototypes -Wno-trigraphs -fno-strict-aliasing=20
> -fno-common -fshort-wchar -fno-PIE -Werror=3Dimplicit-function-declaratio=
n=20
> -Werror=3Dimplicit-int -Werror=3Dreturn-type -Wno-format-security -std=3D=
gnu89=20
> -mbig-endian -m64 -msoft-float -pipe -mtraceback=3Dno -mabi=3Delfv1=20
> -mcall-aixdesc -mcmodel=3Dmedium -mno-pointers-to-nested-functions=20
> -mtune=3Dpower7 -mcpu=3Dpower5 -mno-altivec -mno-vsx=20
> -fno-asynchronous-unwind-tables -mno-string -Wa,-maltivec -Wa,-mpower4=20
> -Wa,-many -mabi=3Delfv1 -mcall-aixdesc -mbig-endian=20
> -mstack-protector-guard=3Dtls -mstack-protector-guard-reg=3Dr13=20
> -fno-delete-null-pointer-checks -Wno-frame-address=20
> -Wno-format-truncation -Wno-format-overflow=20
> -Wno-address-of-packed-member -O2 -fno-allow-store-data-races=20
> -Wframe-larger-than=3D2048 -fstack-protector-strong=20
> -Wimplicit-fallthrough=3D5 -Wno-main -Wno-unused-but-set-variable=20
> -Wno-unused-const-variable -fno-stack-clash-protection=20
> -Wdeclaration-after-statement -Wvla -Wno-pointer-sign=20
> -Wcast-function-type -Wno-stringop-truncation -Wno-zero-length-bounds=20
> -Wno-array-bounds -Wno-stringop-overflow -Wno-restrict=20
> -Wno-maybe-uninitialized -Wno-alloc-size-larger-than=20
> -fno-strict-overflow -fno-stack-check -fconserve-stack -Werror=3Ddate-tim=
e=20
> -Werror=3Dincompatible-pointer-types -Werror=3Ddesignated-init=20
> -Wno-packed-not-aligned -mstack-protector-guard-offset=3D3200 -shared=20
> -fno-common -fno-builtin -nostdlib -Wl,--hash-style=3Dboth -include=20
> /home/chleroy/linux-powerpc/lib/vdso/gettimeofday.c -fno-stack-protector=20
> -DDISABLE_BRANCH_PROFILING -ffreestanding -fasynchronous-unwind-tables=20
> -ffixed-r30=20
> -DKBUILD_MODFILE=3D'"arch/powerpc/kernel/vdso/vgettimeofday-64"'=20
> -DKBUILD_BASENAME=3D'"vgettimeofday_64"'=20
> -DKBUILD_MODNAME=3D'"vgettimeofday_64"'=20
> -D__KBUILD_MODNAME=3Dkmod_vgettimeofday_64 -c -o=20
> arch/powerpc/kernel/vdso/vgettimeofday-64.o=20
> arch/powerpc/kernel/vdso/vgettimeofday.c  ; ./tools/objtool/objtool=20
> mcount arch/powerpc/kernel/vdso/vgettimeofday-64.o

We don't enable ftrace for vdso, so I suspect objtool run above will be=20
a no-op. This needs to be confirmed, of course.


- Naveen