From: Will Deacon <will@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
linux-arm-kernel@lists.infradead.org, mhiramat@kernel.org,
revest@chromium.org, rostedt@goodmis.org
Subject: Re: [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS
Date: Fri, 18 Nov 2022 14:09:52 +0000 [thread overview]
Message-ID: <20221118140951.GE4046@willie-the-truck> (raw)
In-Reply-To: <Y3ePYOxwPbSzxhoZ@FVFF77S0Q05N.cambridge.arm.com>
On Fri, Nov 18, 2022 at 01:57:52PM +0000, Mark Rutland wrote:
> On Fri, Nov 18, 2022 at 12:31:50PM +0000, Will Deacon wrote:
> > On Thu, Nov 17, 2022 at 10:52:15AM +0000, Mark Rutland wrote:
> > > On Tue, Nov 15, 2022 at 11:27:03AM +0000, Will Deacon wrote:
> > > > On Thu, Nov 03, 2022 at 05:05:20PM +0000, Mark Rutland wrote:
> > > > > +static __always_inline unsigned long
> > > > > +ftrace_regs_get_argument(struct ftrace_regs *fregs, unsigned int n)
> > > > > +{
> > > > > + if (n < 8)
> > > > > + return fregs->regs[n];
> > > >
> > > > Where does this '8' come from?
> > >
> > > Because in AAPCS64 the arguments are in x0 to x7, as mentioned in the commit
> > > message:
> > >
> > > | Per AAPCS64, all function call argument and return values are held in
> > > | the following GPRs:
> > > |
> > > | * X0 - X7 : parameter / result registers
> > > | * X8 : indirect result location register
> > > | * SP : stack pointer (AKA SP)
> > >
> > > The 'indirect result location register' would be used when returning large
> > > structures, and isn't a function argument as such.
> >
> > Ah gotcha, I was mainly wondering about the role of x8 in 'struct
> > ftrace_regs', but now I see that the FETCH_OP_REG might want to get at that.
>
> Ah, I see. Should I just add the bits above from the commit message into a
> comment block above the definition of struct ftrace_regs ?
Nah, it's ok, mainly just me learning what this is doing and I've queued it
locally now.
Will
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next prev parent reply other threads:[~2022-11-18 14:11 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-03 17:05 [PATCH v2 0/4] arm64/ftrace: move to DYNAMIC_FTRACE_WITH_ARGS Mark Rutland
2022-11-03 17:05 ` [PATCH v2 1/4] ftrace: pass fregs to arch_ftrace_set_direct_caller() Mark Rutland
2022-11-03 17:05 ` [PATCH v2 2/4] ftrace: rename ftrace_instruction_pointer_set() -> ftrace_regs_set_instruction_pointer() Mark Rutland
2022-11-03 17:05 ` [PATCH v2 3/4] ftrace: abstract DYNAMIC_FTRACE_WITH_ARGS accesses Mark Rutland
2022-11-03 17:05 ` [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS Mark Rutland
2022-11-15 11:27 ` Will Deacon
2022-11-17 10:52 ` Mark Rutland
2022-11-18 12:31 ` Will Deacon
2022-11-18 13:57 ` Mark Rutland
2022-11-18 14:09 ` Will Deacon [this message]
2022-11-15 15:01 ` [PATCH v2 0/4] arm64/ftrace: move to DYNAMIC_FTRACE_WITH_ARGS Steven Rostedt
2022-11-15 15:48 ` Mark Rutland
2022-11-18 0:04 ` Masami Hiramatsu
2022-11-18 19:40 ` Will Deacon
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