On 20.01.2021 17:20, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@xxxxxxxxx>
>
> On ARCH=um, loading a module doesn't result in its constructors
> getting called, which breaks module gcov since the debugfs files
> are never registered. On the other hand, in-kernel constructors
> have already been called by the dynamic linker, so we can't call
> them again.
>
> Get out of this conundrum by allowing CONFIG_CONSTRUCTORS to be
> selected, but avoiding the in-kernel constructor calls.
>
> Also remove the "if !UML" from GCOV selecting CONSTRUCTORS now,
> since we really do want CONSTRUCTORS, just not kernel binary
> ones.
>
> Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Looks good+nicer than v1 to me!
I also tested this patch on s390 and can confirm that it doesn't break
gcov-kernel there.
Reviewed-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
Andrew, do we need additional reviews/sign-offs? Could this go in via
your tree?
> ---
> Tested with a kernel configured with CONFIG_GCOV_KERNEL, without
> the patch nothing ever appears in /sys/kernel/debug/gcov/ (apart
> from the reset file), and with it we get the files and they work.
Just to be sure: could you confirm that this test statement for UML also
applies to v2, i.e. that it fixes the original problem you were seeing?
>
> v2:
> * special-case UML instead of splitting the CONSTRUCTORS config
> ---
> init/Kconfig | 1 -
> init/main.c | 8 +++++++-
> kernel/gcov/Kconfig | 2 +-
> 3 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index b77c60f8b963..29ad68325028 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -76,7 +76,6 @@ config CC_HAS_ASM_INLINE
>
> config CONSTRUCTORS
> bool
> - depends on !UML
>
> config IRQ_WORK
> bool
> diff --git a/init/main.c b/init/main.c
> index c68d784376ca..a626e78dbf06 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1066,7 +1066,13 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
> /* Call all constructor functions linked into the kernel. */
> static void __init do_ctors(void)
> {
> -#ifdef CONFIG_CONSTRUCTORS
> +/*
> + * For UML, the constructors have already been called by the
> + * normal setup code as it's just a normal ELF binary, so we
> + * cannot do it again - but we do need CONFIG_CONSTRUCTORS
> + * even on UML for modules.
> + */
> +#if defined(CONFIG_CONSTRUCTORS) && !defined(CONFIG_UML)
> ctor_fn_t *fn = (ctor_fn_t *) __ctors_start;
>
> for (; fn < (ctor_fn_t *) __ctors_end; fn++)
> diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
> index 3110c77230c7..f62de2dea8a3 100644
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -4,7 +4,7 @@ menu "GCOV-based kernel profiling"
> config GCOV_KERNEL
> bool "Enable gcov-based kernel profiling"
> depends on DEBUG_FS
> - select CONSTRUCTORS if !UML
> + select CONSTRUCTORS
> default n
> help
> This option enables gcov-based code profiling (e.g. for code coverage
>
--
Peter Oberparleiter
Linux on Z Development - IBM Germany
