Re: [PATCH 1/3] ARM64: perf: add support for perf registers API

[Will Deacon <will.deacon@arm.com>]

Hi Jean,

Thanks for the updated patches. One minor comment on this one.

On Mon, Dec 30, 2013 at 04:25:30PM +0000, Jean Pihet wrote:
> From: Jean Pihet <jean.pihet@newoldbits.com>
> 
> This patch implements the functions required for the perf registers API,
> allowing the perf tool to interface kernel register dumps with libunwind
> in order to provide userspace backtracing.
> Compat mode is also supported.

[...]

> +u64 perf_reg_value(struct pt_regs *regs, int idx)
> +{
> +	if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM64_MAX))
> +		return 0;

While this is probably fine, I'd feel more comfortable if you had separate
limit checks for native and compat...

> +	/*
> +	 * Compat (i.e. 32 bit) mode:
> +	 * - PC has been set in the pt_regs struct in kernel_entry,
> +	 * - Handle SP and LR here.
> +	 */
> +	if (compat_user_mode(regs)) {

i.e. have a WARN_ON_ONCE here for the compat structure size.

> +		if ((u32)idx == PERF_REG_ARM64_SP)
> +			return regs->compat_sp;
> +		if ((u32)idx == PERF_REG_ARM64_LR)
> +			return regs->compat_lr;
> +	}

then stick an else here with the original check.

Make sense?

Will