Hi Will, On Wed, 3 Apr 2019 13:06:49 +0100 Will Deacon <[email protected]> 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 <[email protected]> > > --- > > 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? (Of course any SIMD/float parameter passed to the function, it also can not correctly get, but in the kernel we can ignore it.) > > +static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs, > > + unsigned int n) > > +{ > > +#define NR_REG_ARGUMENTS 8 > > + if (n < NR_REG_ARGUMENTS) > > + return regs_get_register(regs, n << 3); > > You can use pt_regs_read_reg() to avoid the shift here. Ah, right! Thank you, -- Masami Hiramatsu <[email protected]>
