[linux-next:master 10774/15793] kernel/kcsan/core.c:829:1: warning: no previous prototype for function '__tsan_volatile_read1'
3:42 a.m.
tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head: af30725c132e2e5c5369b60369ff0771fde7d4ff
commit: 4e23395b9e97562d12b87a330a2fca3bf10c8663 [10774/15793] kcsan: Support
distinguishing volatile accesses
config: x86_64-randconfig-r013-20200605 (attached as .config)
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project
6dd738e2f0609f7d3313b574a1d471263d2d3ba1)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
chmod +x ~/bin/make.cross
# install x86_64 cross compiling tool for clang build
# apt-get install binutils-x86-64-linux-gnu
git checkout 4e23395b9e97562d12b87a330a2fca3bf10c8663
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp(a)intel.com>
All warnings (new ones prefixed by >>, old ones prefixed by <<):
DEFINE_TSAN_READ_WRITE(4);
^
kernel/kcsan/core.c:757:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
<scratch space>:92:1: note: expanded from here
__tsan_read4
^
kernel/kcsan/core.c:776:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_READ_WRITE(4);
^
static
kernel/kcsan/core.c:757:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
kernel/kcsan/core.c:776:1: warning: no previous prototype for function
'__tsan_write4' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(4);
^
kernel/kcsan/core.c:765:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
<scratch space>:126:1: note: expanded from here
__tsan_write4
^
kernel/kcsan/core.c:776:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:765:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
kernel/kcsan/core.c:777:1: warning: no previous prototype for function
'__tsan_read8' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(8);
^
kernel/kcsan/core.c:757:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
<scratch space>:160:1: note: expanded from here
__tsan_read8
^
kernel/kcsan/core.c:777:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_READ_WRITE(8);
^
static
kernel/kcsan/core.c:757:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
kernel/kcsan/core.c:777:1: warning: no previous prototype for function
'__tsan_write8' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(8);
^
kernel/kcsan/core.c:765:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
<scratch space>:15:1: note: expanded from here
__tsan_write8
^
kernel/kcsan/core.c:777:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:765:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
kernel/kcsan/core.c:778:1: warning: no previous prototype for function
'__tsan_read16' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(16);
^
kernel/kcsan/core.c:757:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
<scratch space>:49:1: note: expanded from here
__tsan_read16
^
kernel/kcsan/core.c:778:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_READ_WRITE(16);
^
static
kernel/kcsan/core.c:757:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
kernel/kcsan/core.c:778:1: warning: no previous prototype for function
'__tsan_write16' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(16);
^
kernel/kcsan/core.c:765:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
<scratch space>:83:1: note: expanded from here
__tsan_write16
^
kernel/kcsan/core.c:778:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:765:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_write##size(void *ptr) ^
kernel/kcsan/core.c:780:6: warning: no previous prototype for function
'__tsan_read_range' [-Wmissing-prototypes]
void __tsan_read_range(void *ptr, size_t size)
^
kernel/kcsan/core.c:780:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
void __tsan_read_range(void *ptr, size_t size)
^
static
kernel/kcsan/core.c:786:6: warning: no previous prototype for function
'__tsan_write_range' [-Wmissing-prototypes]
void __tsan_write_range(void *ptr, size_t size)
^
kernel/kcsan/core.c:786:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
void __tsan_write_range(void *ptr, size_t size)
^
static
> kernel/kcsan/core.c:829:1: warning: no previous prototype for
function '__tsan_volatile_read1' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(1);
^
kernel/kcsan/core.c:802:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
<scratch space>:145:1: note: expanded from here
__tsan_volatile_read1
^
kernel/kcsan/core.c:829:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_VOLATILE_READ_WRITE(1);
^
static
kernel/kcsan/core.c:802:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
> kernel/kcsan/core.c:829:1: warning: no previous prototype for
function '__tsan_volatile_write1' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(1);
^
kernel/kcsan/core.c:814:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
<scratch space>:18:1: note: expanded from here
__tsan_volatile_write1
^
kernel/kcsan/core.c:829:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:814:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
> kernel/kcsan/core.c:830:1: warning: no previous prototype for
function '__tsan_volatile_read2' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(2);
^
kernel/kcsan/core.c:802:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
<scratch space>:56:1: note: expanded from here
__tsan_volatile_read2
^
kernel/kcsan/core.c:830:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_VOLATILE_READ_WRITE(2);
^
static
kernel/kcsan/core.c:802:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
> kernel/kcsan/core.c:830:1: warning: no previous prototype for
function '__tsan_volatile_write2' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(2);
^
kernel/kcsan/core.c:814:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
<scratch space>:94:1: note: expanded from here
__tsan_volatile_write2
^
kernel/kcsan/core.c:830:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:814:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
> kernel/kcsan/core.c:831:1: warning: no previous prototype for
function '__tsan_volatile_read4' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(4);
^
kernel/kcsan/core.c:802:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
<scratch space>:6:1: note: expanded from here
__tsan_volatile_read4
^
kernel/kcsan/core.c:831:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_VOLATILE_READ_WRITE(4);
^
static
kernel/kcsan/core.c:802:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
> kernel/kcsan/core.c:831:1: warning: no previous prototype for
function '__tsan_volatile_write4' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(4);
^
kernel/kcsan/core.c:814:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
<scratch space>:44:1: note: expanded from here
__tsan_volatile_write4
^
kernel/kcsan/core.c:831:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:814:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
> kernel/kcsan/core.c:832:1: warning: no previous prototype for
function '__tsan_volatile_read8' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(8);
^
kernel/kcsan/core.c:802:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
<scratch space>:82:1: note: expanded from here
__tsan_volatile_read8
^
kernel/kcsan/core.c:832:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_VOLATILE_READ_WRITE(8);
^
static
kernel/kcsan/core.c:802:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
> kernel/kcsan/core.c:832:1: warning: no previous prototype for
function '__tsan_volatile_write8' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(8);
^
kernel/kcsan/core.c:814:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
<scratch space>:120:1: note: expanded from here
__tsan_volatile_write8
^
kernel/kcsan/core.c:832:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:814:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
> kernel/kcsan/core.c:833:1: warning: no previous prototype for
function '__tsan_volatile_read16' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(16);
^
kernel/kcsan/core.c:802:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
<scratch space>:30:1: note: expanded from here
__tsan_volatile_read16
^
kernel/kcsan/core.c:833:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_VOLATILE_READ_WRITE(16);
^
static
kernel/kcsan/core.c:802:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_read##size(void *ptr) ^
> kernel/kcsan/core.c:833:1: warning: no previous prototype for
function '__tsan_volatile_write16' [-Wmissing-prototypes]
DEFINE_TSAN_VOLATILE_READ_WRITE(16);
^
kernel/kcsan/core.c:814:7: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
<scratch space>:68:1: note: expanded from here
__tsan_volatile_write16
^
kernel/kcsan/core.c:833:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
kernel/kcsan/core.c:814:2: note: expanded from macro
'DEFINE_TSAN_VOLATILE_READ_WRITE'
void __tsan_volatile_write##size(void *ptr) ^
kernel/kcsan/core.c:839:6: warning: no previous prototype for function
'__tsan_func_entry' [-Wmissing-prototypes]
void __tsan_func_entry(void *call_pc)
^
kernel/kcsan/core.c:839:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
void __tsan_func_entry(void *call_pc)
^
static
kernel/kcsan/core.c:843:6: warning: no previous prototype for function
'__tsan_func_exit' [-Wmissing-prototypes]
void __tsan_func_exit(void)
^
kernel/kcsan/core.c:843:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
void __tsan_func_exit(void)
^
static
kernel/kcsan/core.c:847:6: warning: no previous prototype for function
'__tsan_init' [-Wmissing-prototypes]
void __tsan_init(void)
^
kernel/kcsan/core.c:847:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
void __tsan_init(void)
^
static
25 warnings generated.
vim +/__tsan_volatile_read1 +829 kernel/kcsan/core.c
791
792 /*
793 * Use of explicit volatile is generally disallowed [1], however, volatile is
794 * still used in various concurrent context, whether in low-level
795 * synchronization primitives or for legacy reasons.
796 * [1] https://lwn.net/Articles/233479/
797 *
798 * We only consider volatile accesses atomic if they are aligned and would pass
799 * the size-check of compiletime_assert_rwonce_type().
800 */
801 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \
802 void __tsan_volatile_read##size(void *ptr) \
803 { \
804 const bool is_atomic = size <= sizeof(long long) && \
805 IS_ALIGNED((unsigned long)ptr, size); \
806 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
807 return; \
808 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \
809 } \
810 EXPORT_SYMBOL(__tsan_volatile_read##size); \
811 void __tsan_unaligned_volatile_read##size(void *ptr) \
812 __alias(__tsan_volatile_read##size); \
813 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \
814 void __tsan_volatile_write##size(void *ptr) \
815 { \
816 const bool is_atomic = size <= sizeof(long long) && \
817 IS_ALIGNED((unsigned long)ptr, size); \
818 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
819 return; \
820 check_access(ptr, size, \
821 KCSAN_ACCESS_WRITE | \
822 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \
823 } \
824 EXPORT_SYMBOL(__tsan_volatile_write##size); \
825 void __tsan_unaligned_volatile_write##size(void *ptr) \
826 __alias(__tsan_volatile_write##size); \
827 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
828
829 DEFINE_TSAN_VOLATILE_READ_WRITE(1);
830 DEFINE_TSAN_VOLATILE_READ_WRITE(2);
831 DEFINE_TSAN_VOLATILE_READ_WRITE(4);
832 DEFINE_TSAN_VOLATILE_READ_WRITE(8);
833 DEFINE_TSAN_VOLATILE_READ_WRITE(16);
834
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
3:57 a.m.
On Fri, 5 Jun 2020 at 19:42, kernel test robot <lkp(a)intel.com> wrote:
tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head: af30725c132e2e5c5369b60369ff0771fde7d4ff
commit: 4e23395b9e97562d12b87a330a2fca3bf10c8663 [10774/15793] kcsan: Support
distinguishing volatile accesses
config: x86_64-randconfig-r013-20200605 (attached as .config)
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project
6dd738e2f0609f7d3313b574a1d471263d2d3ba1)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
chmod +x ~/bin/make.cross
# install x86_64 cross compiling tool for clang build
# apt-get install binutils-x86-64-linux-gnu
git checkout 4e23395b9e97562d12b87a330a2fca3bf10c8663
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp(a)intel.com>
All warnings (new ones prefixed by >>, old ones prefixed by <<):
DEFINE_TSAN_READ_WRITE(4);
^
kernel/kcsan/core.c:757:7: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
<scratch space>:92:1: note: expanded from here
__tsan_read4
^
kernel/kcsan/core.c:776:1: note: declare 'static' if the function is not intended
to be used outside of this translation unit
DEFINE_TSAN_READ_WRITE(4);
^
static
kernel/kcsan/core.c:757:2: note: expanded from macro 'DEFINE_TSAN_READ_WRITE'
void __tsan_read##size(void *ptr) ^
kernel/kcsan/core.c:776:1: warning: no previous prototype for function
'__tsan_write4' [-Wmissing-prototypes]
DEFINE_TSAN_READ_WRITE(4);
^
[...]
In the case here (and for all other *SAN or compiler-based
instrumentation), it's clearly fine since the compiler is the one
emitting calls to them.
How is one meant to act on W=1 reports like this? The kernel seems to
be full of these. It seems wrong, just to shut up W=1, to start adding
-Wno-missing-prototypes everywhere.
Thanks,
-- Marco
5:13 a.m.
On Fri, Jun 5, 2020 at 10:58 AM 'Marco Elver' via Clang Built Linux
<clang-built-linux(a)googlegroups.com> wrote:
On Fri, 5 Jun 2020 at 19:42, kernel test robot <lkp(a)intel.com> wrote:
>
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head: af30725c132e2e5c5369b60369ff0771fde7d4ff
> commit: 4e23395b9e97562d12b87a330a2fca3bf10c8663 [10774/15793] kcsan: Support
distinguishing volatile accesses
> config: x86_64-randconfig-r013-20200605 (attached as .config)
> compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project
6dd738e2f0609f7d3313b574a1d471263d2d3ba1)
> reproduce (this is a W=1 build):
> wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
> chmod +x ~/bin/make.cross
> # install x86_64 cross compiling tool for clang build
> # apt-get install binutils-x86-64-linux-gnu
> git checkout 4e23395b9e97562d12b87a330a2fca3bf10c8663
> # save the attached .config to linux build tree
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp(a)intel.com>
>
> All warnings (new ones prefixed by >>, old ones prefixed by <<):
>
> DEFINE_TSAN_READ_WRITE(4);
> ^
> kernel/kcsan/core.c:757:7: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> void __tsan_read##size(void *ptr)
^
> <scratch space>:92:1: note: expanded from here
> __tsan_read4
> ^
> kernel/kcsan/core.c:776:1: note: declare 'static' if the function is not
intended to be used outside of this translation unit
> DEFINE_TSAN_READ_WRITE(4);
> ^
> static
> kernel/kcsan/core.c:757:2: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> void __tsan_read##size(void *ptr) ^
> kernel/kcsan/core.c:776:1: warning: no previous prototype for function
'__tsan_write4' [-Wmissing-prototypes]
> DEFINE_TSAN_READ_WRITE(4);
> ^
[...]
In the case here (and for all other *SAN or compiler-based
instrumentation), it's clearly fine since the compiler is the one
emitting calls to them.
How is one meant to act on W=1 reports like this? The kernel seems to
be full of these. It seems wrong, just to shut up W=1, to start adding
-Wno-missing-prototypes everywhere.
+ Philip, because the team is probably getting asked this a lot, and
should link to this response.
`make W=1` enabled -Wmissing-prototypes via scripts/Makfile.extrawarn.
Both GCC and Clang will warn for -Wmissing-prototypes when you define
a function without a previous declaration of it, for non-static
functions. If the linkage is extern, and there was no previous
declaration, then callers may have the wrong signature. Mostly, this
isn't a bug, which is why it's not an error. But sometimes the
signature has changed but the callers have not been updated, which is
an ABI breakage resulting in a bug. Mostly this is not an issue due
to -Wimplicit-function-declaration being on by default, which also
helps in this case.
See: https://godbolt.org/z/aYrYfS
Functions with external linkage should have a forward declaration, or
be marked static if in a .c file, or be marked static inline if in a
header file.
For this specific case, it looks like kcsan.h should forward declare
the functions defined by DEFINE_TSAN_READ_WRITE, to avoid any ABI
mismatch due to different call signatures between callers and callee.
Though I can't see where the callees are; if they're only within
kernel/kcsan/core.c, then defining them as static qualified may be
better. (Probably not, since they're exported via EXPORT_SYMBOL).
--
Thanks,
~Nick Desaulniers
5:44 a.m.
On Fri, 5 Jun 2020 at 21:13, Nick Desaulniers <ndesaulniers(a)google.com> wrote:
On Fri, Jun 5, 2020 at 10:58 AM 'Marco Elver' via Clang Built Linux
<clang-built-linux(a)googlegroups.com> wrote:
>
> On Fri, 5 Jun 2020 at 19:42, kernel test robot <lkp(a)intel.com> wrote:
> >
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
master
> > head: af30725c132e2e5c5369b60369ff0771fde7d4ff
> > commit: 4e23395b9e97562d12b87a330a2fca3bf10c8663 [10774/15793] kcsan: Support
distinguishing volatile accesses
> > config: x86_64-randconfig-r013-20200605 (attached as .config)
> > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project
6dd738e2f0609f7d3313b574a1d471263d2d3ba1)
> > reproduce (this is a W=1 build):
> > wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > # install x86_64 cross compiling tool for clang build
> > # apt-get install binutils-x86-64-linux-gnu
> > git checkout 4e23395b9e97562d12b87a330a2fca3bf10c8663
> > # save the attached .config to linux build tree
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp(a)intel.com>
> >
> > All warnings (new ones prefixed by >>, old ones prefixed by <<):
> >
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> > kernel/kcsan/core.c:757:7: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> > void __tsan_read##size(void *ptr)
^
> > <scratch space>:92:1: note: expanded from here
> > __tsan_read4
> > ^
> > kernel/kcsan/core.c:776:1: note: declare 'static' if the function is
not intended to be used outside of this translation unit
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> > static
> > kernel/kcsan/core.c:757:2: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> > void __tsan_read##size(void *ptr)
^
> > kernel/kcsan/core.c:776:1: warning: no previous prototype for function
'__tsan_write4' [-Wmissing-prototypes]
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> [...]
>
> In the case here (and for all other *SAN or compiler-based
> instrumentation), it's clearly fine since the compiler is the one
> emitting calls to them.
I should have probably said "the compiler is the one emitting calls
due to sanitizer instrumentation" to be clearer.
> How is one meant to act on W=1 reports like this? The kernel
seems to
> be full of these. It seems wrong, just to shut up W=1, to start adding
> -Wno-missing-prototypes everywhere.
+ Philip, because the team is probably getting asked this a lot, and
should link to this response.
`make W=1` enabled -Wmissing-prototypes via scripts/Makfile.extrawarn.
Both GCC and Clang will warn for -Wmissing-prototypes when you define
a function without a previous declaration of it, for non-static
functions. If the linkage is extern, and there was no previous
declaration, then callers may have the wrong signature. Mostly, this
isn't a bug, which is why it's not an error. But sometimes the
signature has changed but the callers have not been updated, which is
an ABI breakage resulting in a bug. Mostly this is not an issue due
to -Wimplicit-function-declaration being on by default, which also
helps in this case.
See: https://godbolt.org/z/aYrYfS
Functions with external linkage should have a forward declaration, or
be marked static if in a .c file, or be marked static inline if in a
header file.
For this specific case, it looks like kcsan.h should forward declare
the functions defined by DEFINE_TSAN_READ_WRITE, to avoid any ABI
mismatch due to different call signatures between callers and callee.
Though I can't see where the callees are; if they're only within
kernel/kcsan/core.c, then defining them as static qualified may be
better. (Probably not, since they're exported via EXPORT_SYMBOL).
Thanks for the explanation. And I agree in the general case this is a
fine warning.
However, the functions here should not be forward declared anywhere,
as they should *only* be emitted by the compiler due to sanitizer
instrumentation. In the case here it's "-fsanitize=thread". Same thing
for KASAN with "-fsanitize=kernel-address". Or UBSAN. None of them
should be forward declared for access by other parts of the kernel
explicitly. Forward declaring these also doesn't help prevent ABI
breakage, since it's the compiler generating the calls.
Let me rephrase my question: what is the idiomatic way to deal with
the warnings for the sanitizers, where the functions are runtime
functions only emitted by the compiler due to instrumentation? We can
add forward declarations 1 line above where they are defined, just for
the sake of shutting up the warning specifically for these functions.
I can send a patch if that's what we want.
Thanks,
-- Marco
5:54 a.m.
On Fri, Jun 5, 2020 at 12:44 PM Marco Elver <elver(a)google.com> wrote:
Let me rephrase my question: what is the idiomatic way to deal with
the warnings for the sanitizers, where the functions are runtime
functions only emitted by the compiler due to instrumentation? We can
add forward declarations 1 line above where they are defined, just for
the sake of shutting up the warning specifically for these functions.
I can send a patch if that's what we want.
I don't know that's there's an idiomatic way for the specific case of
compiler emitted calls, but your suggestion sounds fine. You can test
it with `make W=1` or manually setting `-Wmissing-prototypes` for
KBUILD_CFLAGS. (I think you can even set that variable to that string
in a make command line arg, ie. `make
KBUILD_CFLAGS="-Wmissing-prototypes` (untested).
--
Thanks,
~Nick Desaulniers
10:45 a.m.
On Fri, Jun 05, 2020 at 12:13:36PM -0700, Nick Desaulniers wrote:
On Fri, Jun 5, 2020 at 10:58 AM 'Marco Elver' via Clang Built
Linux
<clang-built-linux(a)googlegroups.com> wrote:
>
> On Fri, 5 Jun 2020 at 19:42, kernel test robot <lkp(a)intel.com> wrote:
> >
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
master
> > head: af30725c132e2e5c5369b60369ff0771fde7d4ff
> > commit: 4e23395b9e97562d12b87a330a2fca3bf10c8663 [10774/15793] kcsan: Support
distinguishing volatile accesses
> > config: x86_64-randconfig-r013-20200605 (attached as .config)
> > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project
6dd738e2f0609f7d3313b574a1d471263d2d3ba1)
> > reproduce (this is a W=1 build):
> > wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > # install x86_64 cross compiling tool for clang build
> > # apt-get install binutils-x86-64-linux-gnu
> > git checkout 4e23395b9e97562d12b87a330a2fca3bf10c8663
> > # save the attached .config to linux build tree
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp(a)intel.com>
> >
> > All warnings (new ones prefixed by >>, old ones prefixed by <<):
> >
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> > kernel/kcsan/core.c:757:7: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> > void __tsan_read##size(void *ptr)
^
> > <scratch space>:92:1: note: expanded from here
> > __tsan_read4
> > ^
> > kernel/kcsan/core.c:776:1: note: declare 'static' if the function is
not intended to be used outside of this translation unit
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> > static
> > kernel/kcsan/core.c:757:2: note: expanded from macro
'DEFINE_TSAN_READ_WRITE'
> > void __tsan_read##size(void *ptr)
^
> > kernel/kcsan/core.c:776:1: warning: no previous prototype for function
'__tsan_write4' [-Wmissing-prototypes]
> > DEFINE_TSAN_READ_WRITE(4);
> > ^
> [...]
>
> In the case here (and for all other *SAN or compiler-based
> instrumentation), it's clearly fine since the compiler is the one
> emitting calls to them.
>
> How is one meant to act on W=1 reports like this? The kernel seems to
> be full of these. It seems wrong, just to shut up W=1, to start adding
> -Wno-missing-prototypes everywhere.
+ Philip, because the team is probably getting asked this a lot, and
should link to this response.
thanks a lot, i had added your response at
https://github.com/intel/lkp-tests/wiki/LKP-FAQ
which is very helpful to explain this.
>
> `make W=1` enabled -Wmissing-prototypes via scripts/Makfile.extrawarn.
>
> Both GCC and Clang will warn for -Wmissing-prototypes when you define
> a function without a previous declaration of it, for non-static
> functions. If the linkage is extern, and there was no previous
> declaration, then callers may have the wrong signature. Mostly, this
> isn't a bug, which is why it's not an error. But sometimes the
> signature has changed but the callers have not been updated, which is
> an ABI breakage resulting in a bug. Mostly this is not an issue due
> to -Wimplicit-function-declaration being on by default, which also
> helps in this case.
>
> See: https://godbolt.org/z/aYrYfS
>
> Functions with external linkage should have a forward declaration, or
> be marked static if in a .c file, or be marked static inline if in a
> header file.
>
> For this specific case, it looks like kcsan.h should forward declare
> the functions defined by DEFINE_TSAN_READ_WRITE, to avoid any ABI
> mismatch due to different call signatures between callers and callee.
> Though I can't see where the callees are; if they're only within
> kernel/kcsan/core.c, then defining them as static qualified may be
> better. (Probably not, since they're exported via EXPORT_SYMBOL).
> --
> Thanks,
> ~Nick Desaulniers
834
days inactive
837
days old
5 comments
4 participants
participants (4)
-
kernel test robot -
Marco Elver -
Nick Desaulniers -
Philip Li