Messages in this thread | | | Date | Fri, 18 Nov 2022 14:09:52 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS |
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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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