On 3/14/24 06:36, Geert Uytterhoeven wrote:
> Hi Günter,
>
> On Tue, Mar 12, 2024 at 6:03 PM Guenter Roeck <[email protected]> wrote:
>> Some unit tests intentionally trigger warning backtraces by passing bad
>> parameters to kernel API functions. Such unit tests typically check the
>> return value from such calls, not the existence of the warning backtrace.
>>
>> Such intentionally generated warning backtraces are neither desirable
>> nor useful for a number of reasons.
>> - They can result in overlooked real problems.
>> - A warning that suddenly starts to show up in unit tests needs to be
>> investigated and has to be marked to be ignored, for example by
>> adjusting filter scripts. Such filters are ad-hoc because there is
>> no real standard format for warnings. On top of that, such filter
>> scripts would require constant maintenance.
>>
>> One option to address problem would be to add messages such as "expected
>> warning backtraces start / end here" to the kernel log. However, that
>> would again require filter scripts, it might result in missing real
>> problematic warning backtraces triggered while the test is running, and
>> the irrelevant backtrace(s) would still clog the kernel log.
>>
>> Solve the problem by providing a means to identify and suppress specific
>> warning backtraces while executing test code. Support suppressing multiple
>> backtraces while at the same time limiting changes to generic code to the
>> absolute minimum. Architecture specific changes are kept at minimum by
>> retaining function names only if both CONFIG_DEBUG_BUGVERBOSE and
>> CONFIG_KUNIT are enabled.
>>
>> The first patch of the series introduces the necessary infrastructure.
>> The second patch introduces support for counting suppressed backtraces.
>> This capability is used in patch three to implement unit tests.
>> Patch four documents the new API.
>> The next two patches add support for suppressing backtraces in drm_rect
>> and dev_addr_lists unit tests. These patches are intended to serve as
>> examples for the use of the functionality introduced with this series.
>> The remaining patches implement the necessary changes for all
>> architectures with GENERIC_BUG support.
>
> Thanks for your series!
>
> I gave it a try on m68k, just running backtrace-suppression-test,
> and that seems to work fine.
>
>> Design note:
>> Function pointers are only added to the __bug_table section if both
>> CONFIG_KUNIT and CONFIG_DEBUG_BUGVERBOSE are enabled to avoid image
>> size increases if CONFIG_KUNIT=n. There would be some benefits to
>> adding those pointers all the time (reduced complexity, ability to
>> display function names in BUG/WARNING messages). That change, if
>> desired, can be made later.
>
> Unfortunately this also increases kernel size in the CONFIG_KUNIT=m
> case (ca. 80 KiB for atari_defconfig), making it less attractive to have
> kunit and all tests enabled as modules in my standard kernel.
>

Good point. Indeed, it does. I wanted to avoid adding a configuration option,
but maybe I should add it after all. How about something like this ?

+config KUNIT_SUPPRESS_BACKTRACE
+ bool "KUnit - Enable backtrace suppression"
+ default y
+ help
+ Enable backtrace suppression for KUnit. If enabled, backtraces
+ generated intentionally by KUnit tests can be suppressed. Disable
+ to reduce kernel image size if image size is more important than
+ suppression of backtraces generated by KUnit tests.
+

Thanks,
Guenter

2024-03-14 15:02:38

On 3/12/24 18:03, Guenter Roeck wrote:
> Add name of functions triggering warning backtraces to the __bug_table
> object section to enable support for suppressing WARNING backtraces.
>
> To limit image size impact, the pointer to the function name is only added
> to the __bug_table section if both CONFIG_KUNIT and CONFIG_DEBUG_BUGVERBOSE
> are enabled. Otherwise, the __func__ assembly parameter is replaced with a
> (dummy) NULL parameter to avoid an image size increase due to unused
> __func__ entries (this is necessary because __func__ is not a define but a
> virtual variable).
>
> While at it, declare assembler parameters as constants where possible.
> Refine .blockz instructions to calculate the necessary padding instead
> of using fixed values.
>
> Signed-off-by: Guenter Roeck <[email protected]>

Acked-by: Helge Deller <[email protected]>

Helge

> ---
> arch/parisc/include/asm/bug.h | 29 +++++++++++++++++++++--------
> 1 file changed, 21 insertions(+), 8 deletions(-)
>
> diff --git a/arch/parisc/include/asm/bug.h b/arch/parisc/include/asm/bugh
> index 833555f74ffa..792dacc2a653 100644
> --- a/arch/parisc/include/asm/bug.h
> +++ b/arch/parisc/include/asm/bug.h
> @@ -23,8 +23,17 @@
> # define __BUG_REL(val) ".word " __stringify(val)
> #endif
>
> -
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> +
> +#if IS_ENABLED(CONFIG_KUNIT)
> +# define HAVE_BUG_FUNCTION
> +# define __BUG_FUNC_PTR __BUG_REL(%c1)
> +# define __BUG_FUNC __func__
> +#else
> +# define __BUG_FUNC_PTR
> +# define __BUG_FUNC NULL
> +#endif /* IS_ENABLED(CONFIG_KUNIT) */
> +
> #define BUG() \
> do { \
> asm volatile("\n" \
> @@ -33,10 +42,12 @@
> "\t.align 4\n" \
> "2:\t" __BUG_REL(1b) "\n" \
> "\t" __BUG_REL(%c0) "\n" \
> - "\t.short %1, %2\n" \
> - "\t.blockz %3-2*4-2*2\n" \
> + "\t" __BUG_FUNC_PTR "\n" \
> + "\t.short %c2, %c3\n" \
> + "\t.blockz %c4-(.-2b)\n" \
> "\t.popsection" \
> - : : "i" (__FILE__), "i" (__LINE__), \
> + : : "i" (__FILE__), "i" (__BUG_FUNC), \
> + "i" (__LINE__), \
> "i" (0), "i" (sizeof(struct bug_entry)) ); \
> unreachable(); \
> } while(0)
> @@ -58,10 +69,12 @@
> "\t.align 4\n" \
> "2:\t" __BUG_REL(1b) "\n" \
> "\t" __BUG_REL(%c0) "\n" \
> - "\t.short %1, %2\n" \
> - "\t.blockz %3-2*4-2*2\n" \
> + "\t" __BUG_FUNC_PTR "\n" \
> + "\t.short %c2, %3\n" \
> + "\t.blockz %c4-(.-2b)\n" \
> "\t.popsection" \
> - : : "i" (__FILE__), "i" (__LINE__), \
> + : : "i" (__FILE__), "i" (__BUG_FUNC), \
> + "i" (__LINE__), \
> "i" (BUGFLAG_WARNING|(flags)), \
> "i" (sizeof(struct bug_entry)) ); \
> } while(0)
> @@ -74,7 +87,7 @@
> "\t.align 4\n" \
> "2:\t" __BUG_REL(1b) "\n" \
> "\t.short %0\n" \
> - "\t.blockz %1-4-2\n" \
> + "\t.blockz %c1-(.-2b)\n" \
> "\t.popsection" \
> : : "i" (BUGFLAG_WARNING|(flags)), \
> "i" (sizeof(struct bug_entry)) ); \