* [PATCH 1/2] compiler_types: Ensure __diag_clang() is always available
2024-03-19 16:07 [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Nathan Chancellor
@ 2024-03-19 16:07 ` Nathan Chancellor
2024-03-20 0:35 ` Justin Stitt
2024-03-19 16:07 ` [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros Nathan Chancellor
2024-03-19 22:15 ` [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Steven Rostedt
2 siblings, 1 reply; 8+ messages in thread
From: Nathan Chancellor @ 2024-03-19 16:07 UTC (permalink / raw)
To: rostedt, mhiramat
Cc: mathieu.desnoyers, ndesaulniers, morbo, justinstitt, linux-kernel,
linux-trace-kernel, llvm, patches, Nathan Chancellor
Attempting to use __diag_clang() and build with GCC results in a build
error:
include/linux/compiler_types.h:468:38: error: 'ignore' undeclared (first use in this function); did you mean 'inode'?
468 | __diag_ ## compiler(version, ignore, option)
| ^~~~~~
This error occurs because __diag_clang() is only defined in
compiler-clang.h, which is only included when using clang as the
compiler. This error has not been seen before because __diag_clang() has
only been used in __diag_ignore_all(), which is defined in both
compiler-clang.h and compiler-gcc.h.
Add an empty stub for __diag_clang() in compiler_types.h, so that it is
always defined and just becomes a no-op when using GCC.
Fixes: f014a00bbeb0 ("compiler-clang.h: Add __diag infrastructure for clang")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
include/linux/compiler_types.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 3e64ec0f7ac8..fb0c3ff5497d 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -461,6 +461,10 @@ struct ftrace_likely_data {
#define __diag_GCC(version, severity, string)
#endif
+#ifndef __diag_clang
+#define __diag_clang(version, severity, string)
+#endif
+
#define __diag_push() __diag(push)
#define __diag_pop() __diag(pop)
--
2.44.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH 1/2] compiler_types: Ensure __diag_clang() is always available
2024-03-19 16:07 ` [PATCH 1/2] compiler_types: Ensure __diag_clang() is always available Nathan Chancellor
@ 2024-03-20 0:35 ` Justin Stitt
0 siblings, 0 replies; 8+ messages in thread
From: Justin Stitt @ 2024-03-20 0:35 UTC (permalink / raw)
To: Nathan Chancellor
Cc: rostedt, mhiramat, mathieu.desnoyers, ndesaulniers, morbo,
linux-kernel, linux-trace-kernel, llvm, patches
Hi,
On Tue, Mar 19, 2024 at 09:07:52AM -0700, Nathan Chancellor wrote:
> Attempting to use __diag_clang() and build with GCC results in a build
> error:
>
> include/linux/compiler_types.h:468:38: error: 'ignore' undeclared (first use in this function); did you mean 'inode'?
> 468 | __diag_ ## compiler(version, ignore, option)
> | ^~~~~~
>
> This error occurs because __diag_clang() is only defined in
> compiler-clang.h, which is only included when using clang as the
> compiler. This error has not been seen before because __diag_clang() has
> only been used in __diag_ignore_all(), which is defined in both
> compiler-clang.h and compiler-gcc.h.
>
> Add an empty stub for __diag_clang() in compiler_types.h, so that it is
> always defined and just becomes a no-op when using GCC.
>
> Fixes: f014a00bbeb0 ("compiler-clang.h: Add __diag infrastructure for clang")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
> ---
> include/linux/compiler_types.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 3e64ec0f7ac8..fb0c3ff5497d 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -461,6 +461,10 @@ struct ftrace_likely_data {
> #define __diag_GCC(version, severity, string)
> #endif
>
> +#ifndef __diag_clang
> +#define __diag_clang(version, severity, string)
> +#endif
> +
> #define __diag_push() __diag(push)
> #define __diag_pop() __diag(pop)
>
>
> --
> 2.44.0
Thanks
Justin
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros
2024-03-19 16:07 [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Nathan Chancellor
2024-03-19 16:07 ` [PATCH 1/2] compiler_types: Ensure __diag_clang() is always available Nathan Chancellor
@ 2024-03-19 16:07 ` Nathan Chancellor
2024-03-20 0:30 ` Justin Stitt
2024-03-19 22:15 ` [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Steven Rostedt
2 siblings, 1 reply; 8+ messages in thread
From: Nathan Chancellor @ 2024-03-19 16:07 UTC (permalink / raw)
To: rostedt, mhiramat
Cc: mathieu.desnoyers, ndesaulniers, morbo, justinstitt, linux-kernel,
linux-trace-kernel, llvm, patches,
Linux Kernel Functional Testing, Nathan Chancellor
Commit b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON()
check") addressed a clang warning, -Wstring-compare, with the use of
__builtin_constant_p() to dispatch to strcmp() if the source string is a
string literal and a direct comparison if not. Unfortunately, even with
this change, the warning is still present because __builtin_constant_p()
is not evaluated at this stage of the pipeline, so clang still thinks
the else branch could occur for this situation:
include/trace/events/sunrpc.h:705:4: error: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Werror,-Wstring-compare]
...
include/trace/stages/stage6_event_callback.h:40:15: note: expanded from macro '__assign_str'
40 | (src) != __data_offsets.dst##_ptr_); \
| ^
...
Use the compiler diagnostic macros to disable this warning around the
WARN_ON_ONCE() expression since a string comparison function, strcmp(),
will always be used for the comparison of string literals.
Fixes: b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON() check")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/all/CA+G9fYs=OTKAZS6g1P1Ewadfr0qoe6LgOVSohqkXmFXotEODdg@mail.gmail.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
include/trace/stages/stage6_event_callback.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace/stages/stage6_event_callback.h
index 83da83a0c14f..56a4eea5a48e 100644
--- a/include/trace/stages/stage6_event_callback.h
+++ b/include/trace/stages/stage6_event_callback.h
@@ -35,9 +35,14 @@
do { \
char *__str__ = __get_str(dst); \
int __len__ = __get_dynamic_array_len(dst) - 1; \
+ __diag_push(); \
+ __diag_ignore(clang, 11, "-Wstring-compare", \
+ "__builtin_constant_p() ensures strcmp()" \
+ "will be used for string literals"); \
WARN_ON_ONCE(__builtin_constant_p(src) ? \
strcmp((src), __data_offsets.dst##_ptr_) : \
(src) != __data_offsets.dst##_ptr_); \
+ __diag_pop(); \
memcpy(__str__, __data_offsets.dst##_ptr_ ? : \
EVENT_NULL_STR, __len__); \
__str__[__len__] = '\0'; \
--
2.44.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros
2024-03-19 16:07 ` [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros Nathan Chancellor
@ 2024-03-20 0:30 ` Justin Stitt
2024-03-20 0:37 ` Steven Rostedt
0 siblings, 1 reply; 8+ messages in thread
From: Justin Stitt @ 2024-03-20 0:30 UTC (permalink / raw)
To: Nathan Chancellor
Cc: rostedt, mhiramat, mathieu.desnoyers, ndesaulniers, morbo,
linux-kernel, linux-trace-kernel, llvm, patches,
Linux Kernel Functional Testing
On Tue, Mar 19, 2024 at 9:08 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Commit b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON()
> check") addressed a clang warning, -Wstring-compare, with the use of
> __builtin_constant_p() to dispatch to strcmp() if the source string is a
> string literal and a direct comparison if not. Unfortunately, even with
> this change, the warning is still present because __builtin_constant_p()
> is not evaluated at this stage of the pipeline, so clang still thinks
> the else branch could occur for this situation:
>
> include/trace/events/sunrpc.h:705:4: error: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Werror,-Wstring-compare]
> ...
> include/trace/stages/stage6_event_callback.h:40:15: note: expanded from macro '__assign_str'
> 40 | (src) != __data_offsets.dst##_ptr_); \
> | ^
> ...
>
> Use the compiler diagnostic macros to disable this warning around the
> WARN_ON_ONCE() expression since a string comparison function, strcmp(),
> will always be used for the comparison of string literals.
>
> Fixes: b1afefa62ca9 ("tracing: Use strcmp() in __assign_str() WARN_ON() check")
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Closes: https://lore.kernel.org/all/CA+G9fYs=OTKAZS6g1P1Ewadfr0qoe6LgOVSohqkXmFXotEODdg@mail.gmail.com/
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> include/trace/stages/stage6_event_callback.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace/stages/stage6_event_callback.h
> index 83da83a0c14f..56a4eea5a48e 100644
> --- a/include/trace/stages/stage6_event_callback.h
> +++ b/include/trace/stages/stage6_event_callback.h
> @@ -35,9 +35,14 @@
> do { \
> char *__str__ = __get_str(dst); \
> int __len__ = __get_dynamic_array_len(dst) - 1; \
> + __diag_push(); \
> + __diag_ignore(clang, 11, "-Wstring-compare", \
> + "__builtin_constant_p() ensures strcmp()" \
> + "will be used for string literals"); \
> WARN_ON_ONCE(__builtin_constant_p(src) ? \
> strcmp((src), __data_offsets.dst##_ptr_) : \
> (src) != __data_offsets.dst##_ptr_); \
What exactly is the point of the literal string comparison? Why
doesn't strcmp do the trick?
> + __diag_pop(); \
> memcpy(__str__, __data_offsets.dst##_ptr_ ? : \
> EVENT_NULL_STR, __len__); \
> __str__[__len__] = '\0'; \
>
> --
> 2.44.0
>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros
2024-03-20 0:30 ` Justin Stitt
@ 2024-03-20 0:37 ` Steven Rostedt
0 siblings, 0 replies; 8+ messages in thread
From: Steven Rostedt @ 2024-03-20 0:37 UTC (permalink / raw)
To: Justin Stitt
Cc: Nathan Chancellor, mhiramat, mathieu.desnoyers, ndesaulniers,
morbo, linux-kernel, linux-trace-kernel, llvm, patches,
Linux Kernel Functional Testing
On Tue, 19 Mar 2024 17:30:41 -0700
Justin Stitt <justinstitt@google.com> wrote:
> > diff --git a/include/trace/stages/stage6_event_callback.h b/include/trace/stages/stage6_event_callback.h
> > index 83da83a0c14f..56a4eea5a48e 100644
> > --- a/include/trace/stages/stage6_event_callback.h
> > +++ b/include/trace/stages/stage6_event_callback.h
> > @@ -35,9 +35,14 @@
> > do { \
> > char *__str__ = __get_str(dst); \
> > int __len__ = __get_dynamic_array_len(dst) - 1; \
> > + __diag_push(); \
> > + __diag_ignore(clang, 11, "-Wstring-compare", \
> > + "__builtin_constant_p() ensures strcmp()" \
> > + "will be used for string literals"); \
> > WARN_ON_ONCE(__builtin_constant_p(src) ? \
> > strcmp((src), __data_offsets.dst##_ptr_) : \
> > (src) != __data_offsets.dst##_ptr_); \
>
> What exactly is the point of the literal string comparison? Why
> doesn't strcmp do the trick?
This is done in the hotpath, and is only for debugging. The string passed
into __string() should be the same as the string passed into __assign_str().
But this is moot as I ended up always using strcmp() even if it will slow
down the recording of the event.
Next merge window the src parameter (along with the strcmp() checks) are
going away.
-- Steve
>
> > + __diag_pop(); \
> > memcpy(__str__, __data_offsets.dst##_ptr_ ? : \
> > EVENT_NULL_STR, __len__); \
> > __str__[__len__] = '\0'; \
> >
> > --
> > 2.44.0
> >
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare
2024-03-19 16:07 [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Nathan Chancellor
2024-03-19 16:07 ` [PATCH 1/2] compiler_types: Ensure __diag_clang() is always available Nathan Chancellor
2024-03-19 16:07 ` [PATCH 2/2] tracing: Ignore -Wstring-compare with diagnostic macros Nathan Chancellor
@ 2024-03-19 22:15 ` Steven Rostedt
2024-03-19 22:27 ` Nathan Chancellor
2 siblings, 1 reply; 8+ messages in thread
From: Steven Rostedt @ 2024-03-19 22:15 UTC (permalink / raw)
To: Nathan Chancellor
Cc: mhiramat, mathieu.desnoyers, ndesaulniers, morbo, justinstitt,
linux-kernel, linux-trace-kernel, llvm, patches,
Linux Kernel Functional Testing
On Tue, 19 Mar 2024 09:07:51 -0700
Nathan Chancellor <nathan@kernel.org> wrote:
> Hi all,
>
> This series fully resolves the new instance of -Wstring-compare from
> within the __assign_str() macro. The first patch resolves a build
> failure with GCC that would be seen with just the second patch applied.
> The second patch actually hides the warning.
>
> NOTE: This is based on trace/for-next, which does not contain the
> minimum LLVM version bump that occurred later in the current merge
> window, so this uses
>
> __diag_ignore(clang, 11, ...
>
> instead of
>
> __diag_ignore(clang, 13, ...
>
> which will be required when this is merged into Linus's tree. If you can
> base this series on a tree that has the merge commit e5eb28f6d1af ("Merge
> tag 'mm-nonmm-stable-2024-03-14-09-36' of
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm") in it, then that
> change can be done at application time, rather than merge time (or I can
> send a v2). It would be really nice for this to make the merge window so
> that this warning does not proliferate into other trees that base on
> -rc1.
>
I'm guessing this isn't needed with the last update.
-- Steve
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare
2024-03-19 22:15 ` [PATCH 0/2] tracing: Fully silence instance of -Wstring-compare Steven Rostedt
@ 2024-03-19 22:27 ` Nathan Chancellor
0 siblings, 0 replies; 8+ messages in thread
From: Nathan Chancellor @ 2024-03-19 22:27 UTC (permalink / raw)
To: Steven Rostedt
Cc: mhiramat, mathieu.desnoyers, ndesaulniers, morbo, justinstitt,
linux-kernel, linux-trace-kernel, llvm, patches,
Linux Kernel Functional Testing
On Tue, Mar 19, 2024 at 06:15:09PM -0400, Steven Rostedt wrote:
> On Tue, 19 Mar 2024 09:07:51 -0700
> Nathan Chancellor <nathan@kernel.org> wrote:
>
> > Hi all,
> >
> > This series fully resolves the new instance of -Wstring-compare from
> > within the __assign_str() macro. The first patch resolves a build
> > failure with GCC that would be seen with just the second patch applied.
> > The second patch actually hides the warning.
> >
> > NOTE: This is based on trace/for-next, which does not contain the
> > minimum LLVM version bump that occurred later in the current merge
> > window, so this uses
> >
> > __diag_ignore(clang, 11, ...
> >
> > instead of
> >
> > __diag_ignore(clang, 13, ...
> >
> > which will be required when this is merged into Linus's tree. If you can
> > base this series on a tree that has the merge commit e5eb28f6d1af ("Merge
> > tag 'mm-nonmm-stable-2024-03-14-09-36' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm") in it, then that
> > change can be done at application time, rather than merge time (or I can
> > send a v2). It would be really nice for this to make the merge window so
> > that this warning does not proliferate into other trees that base on
> > -rc1.
> >
>
> I'm guessing this isn't needed with the last update.
Correct, this is resolved in Linus's tree and should be in -next
tomorrow. The first patch may be worth sending standalone, I'll think
about sending it later but that can go in via some other tree, not
yours.
Cheers,
Nathan
^ permalink raw reply [flat|nested] 8+ messages in thread