Messages in this thread Patch in this message | | | Date | Fri, 18 Nov 2022 12:31:50 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS |
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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: > > > This commit replaces arm64's support for FTRACE_WITH_REGS with support > > > for FTRACE_WITH_ARGS. This removes some overhead and complexity, and > > > removes some latent issues with inconsistent presentation of struct > > > pt_regs (which can only be reliably saved/restored at exception > > > boundaries). > > > > [...] > > > > > @@ -78,10 +77,71 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) > > > return addr; > > > } > > > > > > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS > > > struct dyn_ftrace; > > > struct ftrace_ops; > > > -struct ftrace_regs; > > > + > > > +#define arch_ftrace_get_regs(regs) NULL > > > + > > > +struct ftrace_regs { > > > + /* x0 - x8 */ > > > + unsigned long regs[9]; > > > + unsigned long __unused; > > > + > > > + unsigned long fp; > > > + unsigned long lr; > > > + > > > + unsigned long sp; > > > + unsigned long pc; > > > +}; > > > + > > > +static __always_inline unsigned long > > > +ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs) > > > +{ > > > + return fregs->pc; > > > +} > > > + > > > +static __always_inline void > > > +ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs, > > > + unsigned long pc) > > > +{ > > > + fregs->pc = pc; > > > +} > > > + > > > +static __always_inline unsigned long > > > +ftrace_regs_get_stack_pointer(const struct ftrace_regs *fregs) > > > +{ > > > + return fregs->sp; > > > +} > > > + > > > +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.
Will
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