"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> writes:
> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
> Rewrite fprobe implementation on function-graph tracer.
> Major API changes are:
> - 'nr_maxactive' field is deprecated.
> - This depends on CONFIG_DYNAMIC_FTRACE_WITH_ARGS or
> !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS, and
> CONFIG_HAVE_FUNCTION_GRAPH_FREGS. So currently works only
> on x86_64.
> - Currently the entry size is limited in 15 * sizeof(long).
> - If there is too many fprobe exit handler set on the same
> function, it will fail to probe.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
> Cc: WANG Xuerui <kernel@xxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: Naveen N Rao <naveen@xxxxxxxxxx>
> Cc: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
> Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
[..]
> diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
> index ef609bcca0f9..2d06bbd99601 100644
> --- a/include/linux/fprobe.h
> +++ b/include/linux/fprobe.h
> @@ -5,10 +5,11 @@
[..]
> +static inline unsigned long encode_fprobe_header(struct fprobe *fp, int size_words)
> +{
> + if (WARN_ON_ONCE(size_words > MAX_FPROBE_DATA_SIZE_WORD ||
> + ((unsigned long)fp & ~FPROBE_HEADER_PTR_MASK) !=
> + ~FPROBE_HEADER_PTR_MASK)) {
> + return 0;
> }
> + return ((unsigned long)size_words << FPROBE_HEADER_PTR_BITS) |
> + ((unsigned long)fp & FPROBE_HEADER_PTR_MASK);
> +}
> +
> +/* Return reserved data size in words */
> +static inline int decode_fprobe_header(unsigned long val, struct fprobe **fp)
> +{
> + unsigned long ptr;
> +
> + ptr = (val & FPROBE_HEADER_PTR_MASK) | ~FPROBE_HEADER_PTR_MASK;
> + if (fp)
> + *fp = (struct fprobe *)ptr;
> + return val >> FPROBE_HEADER_PTR_BITS;
> +}
I think that still has the issue that the size is encoded in the
leftmost fields of the pointer, which doesn't work on all
architectures. I reported this already in v15
(https://lore.kernel.org/all/yt9dmsjyx067.fsf@xxxxxxxxxxxxx/)
