On Thu, 11 Apr 2019 18:22:53 +0100 Will Deacon <will.dea...@arm.com> wrote:
> On Mon, Apr 08, 2019 at 09:33:20AM +0900, Masami Hiramatsu wrote: > > On Wed, 3 Apr 2019 13:06:49 +0100 > > Will Deacon <will.dea...@arm.com> wrote: > > > On Mon, Mar 18, 2019 at 04:59:02PM +0900, Masami Hiramatsu wrote: > > > > Add regs_get_argument() which returns N th argument of the function > > > > call. On arm64, it supports up to 8th argument. > > > > Note that this chooses most probably assignment, in some case > > > > it can be incorrect (e.g. passing data structure or floating > > > > point etc.) > > > > > > > > This enables ftrace kprobe events to access kernel function > > > > arguments via $argN syntax. > > > > > > > > Signed-off-by: Masami Hiramatsu <mhira...@kernel.org> > > > > --- > > > > arch/arm64/Kconfig | 1 + > > > > arch/arm64/include/asm/ptrace.h | 18 ++++++++++++++++++ > > > > 2 files changed, 19 insertions(+) > > > > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > > index 117b2541ef3d..6ba0da4be73c 100644 > > > > --- a/arch/arm64/Kconfig > > > > +++ b/arch/arm64/Kconfig > > > > @@ -148,6 +148,7 @@ config ARM64 > > > > select HAVE_PERF_REGS > > > > select HAVE_PERF_USER_STACK_DUMP > > > > select HAVE_REGS_AND_STACK_ACCESS_API > > > > + select HAVE_FUNCTION_ARG_ACCESS_API > > > > select HAVE_RCU_TABLE_FREE > > > > select HAVE_RCU_TABLE_INVALIDATE > > > > select HAVE_RSEQ > > > > diff --git a/arch/arm64/include/asm/ptrace.h > > > > b/arch/arm64/include/asm/ptrace.h > > > > index ec60174c8c18..cfa1bc9b8b70 100644 > > > > --- a/arch/arm64/include/asm/ptrace.h > > > > +++ b/arch/arm64/include/asm/ptrace.h > > > > @@ -305,6 +305,24 @@ static inline unsigned long > > > > regs_return_value(struct pt_regs *regs) > > > > return regs->regs[0]; > > > > } > > > > > > > > +/** > > > > + * regs_get_kernel_argument() - get Nth function argument in kernel > > > > + * @regs: pt_regs of that context > > > > + * @n: function argument number (start from 0) > > > > + * > > > > + * regs_get_argument() returns @n th argument of the function call. > > > > + * Note that this chooses most probably assignment, in some case > > > > + * it can be incorrect. > > > > > > In which cases would it be incorrect? I can imagine varargs causing > > > problems, but are there others? > > > > As far as I can read "Procedure Call Standard for the ARM 64-bit > > Architecture(AArch64) 5.4.2 Parameter Passing Rules", it may not return > > correct data if the target function has a parameter which is 16bytes > > or bigger size. Of course that is just a limitation of this interface. > > But anyway, it can return wrong data for the parameter after such big > > parameters. I think, for func(data-struct-128bits p1, u64 p2), p1 > > is stored into r0 and r1, and p2 is stored r2, is that correct? > > Oh, yes, passing things by value that don't fit in the registers will > obviously go wrong. Thanks. Do we do that in the kernel? No, as far as I know. But I can't say it never happens in the kernel. > > Anyway, please resend with the comment expanded a bit and using > pt_regs_read_reg(), then I can queue this up for 5.2. OK, I'll do. Thank you! > > Cheers, > > Will -- Masami Hiramatsu <mhira...@kernel.org>