Re: [RFC PATCH 2/3] objtool: Enable and implement 'mcount' subcommand

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 21/03/2022 à 09:19, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>>
>>
>> Le 18/03/2022 à 11:51, Sathvika Vasireddy a écrit :
>>> 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'
>>>
>>> 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
>>>
>>> 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    += -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
>>> +ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
>>> +prepare: tools/objtool
>>> +endif
>>
>> I don't think that will work for powerpc.
>>
>> See arch/powerpc/Makefile
>>
>> powerpc builds the VDSO under prepare: , and powerpc has 
>> CONFIG_HAVE_GENERIC_VDSO so there are some C files in that step that 
>> seem to use objtool, allthough that looks odd to me. Must be something 
>> to fix somewhere.
>>
>>    powerpc64-linux-gcc 
>> -Wp,-MMD,arch/powerpc/kernel/vdso/.vgettimeofday-64.o.d -nostdinc 
>> -I./arch/powerpc/include -I./arch/powerpc/include/generated  
>> -I./include -I./arch/powerpc/include/uapi 
>> -I./arch/powerpc/include/generated/uapi -I./include/uapi 
>> -I./include/generated/uapi -include ./include/linux/compiler-version.h 
>> -include ./include/linux/kconfig.h -include 
>> ./include/linux/compiler_types.h -D__KERNEL__ -I ./arch/powerpc 
>> -DHAVE_AS_ATHIGH=1 -fmacro-prefix-map=./= -Wall -Wundef 
>> -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing 
>> -fno-common -fshort-wchar -fno-PIE 
>> -Werror=implicit-function-declaration -Werror=implicit-int 
>> -Werror=return-type -Wno-format-security -std=gnu89 -mbig-endian -m64 
>> -msoft-float -pipe -mtraceback=no -mabi=elfv1 -mcall-aixdesc 
>> -mcmodel=medium -mno-pointers-to-nested-functions -mtune=power7 
>> -mcpu=power5 -mno-altivec -mno-vsx -fno-asynchronous-unwind-tables 
>> -mno-string -Wa,-maltivec -Wa,-mpower4 -Wa,-many -mabi=elfv1 
>> -mcall-aixdesc -mbig-endian -mstack-protector-guard=tls 
>> -mstack-protector-guard-reg=r13 -fno-delete-null-pointer-checks 
>> -Wno-frame-address -Wno-format-truncation -Wno-format-overflow 
>> -Wno-address-of-packed-member -O2 -fno-allow-store-data-races 
>> -Wframe-larger-than=2048 -fstack-protector-strong 
>> -Wimplicit-fallthrough=5 -Wno-main -Wno-unused-but-set-variable 
>> -Wno-unused-const-variable -fno-stack-clash-protection 
>> -Wdeclaration-after-statement -Wvla -Wno-pointer-sign 
>> -Wcast-function-type -Wno-stringop-truncation -Wno-zero-length-bounds 
>> -Wno-array-bounds -Wno-stringop-overflow -Wno-restrict 
>> -Wno-maybe-uninitialized -Wno-alloc-size-larger-than 
>> -fno-strict-overflow -fno-stack-check -fconserve-stack 
>> -Werror=date-time -Werror=incompatible-pointer-types 
>> -Werror=designated-init -Wno-packed-not-aligned 
>> -mstack-protector-guard-offset=3200 -shared -fno-common -fno-builtin 
>> -nostdlib -Wl,--hash-style=both -include 
>> /home/chleroy/linux-powerpc/lib/vdso/gettimeofday.c 
>> -fno-stack-protector -DDISABLE_BRANCH_PROFILING -ffreestanding 
>> -fasynchronous-unwind-tables -ffixed-r30 
>> -DKBUILD_MODFILE='"arch/powerpc/kernel/vdso/vgettimeofday-64"' 
>> -DKBUILD_BASENAME='"vgettimeofday_64"' 
>> -DKBUILD_MODNAME='"vgettimeofday_64"' 
>> -D__KBUILD_MODNAME=kmod_vgettimeofday_64 -c -o 
>> arch/powerpc/kernel/vdso/vgettimeofday-64.o 
>> arch/powerpc/kernel/vdso/vgettimeofday.c  ; ./tools/objtool/objtool 
>> mcount arch/powerpc/kernel/vdso/vgettimeofday-64.o
> 
> We don't enable ftrace for vdso, so I suspect objtool run above will be 
> a no-op. This needs to be confirmed, of course.
> 

I just checked without the series: recordmcount isn't run for VDSO, so 
objtool shouldn't be run either when the series is applied.

Christophe