linux-kernel - Re: [PATCH] arm64/hw_breakpoint: Determine lengths from generic perf breakpoint macros

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Date: Fri, 23 Feb 2024 12:52:24 +0000
From: Will Deacon <will@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, broonie@...nel.org,
	Mark Rutland <mark.rutland@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/hw_breakpoint: Determine lengths from generic perf
 breakpoint macros

On Fri, Feb 23, 2024 at 05:01:02PM +0530, Anshuman Khandual wrote:
> Both platform i.e ARM_BREAKPOINT_LEN_X and generic i.e HW_BREAKPOINT_LEN_X
> macros are used interchangeably to convert event->attr.bp_len and platform
> breakpoint control arch_hw_breakpoint_ctrl->len. Let's be consistent while
> deriving one from the other. This does not cause any functional changes.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> This applies on v6.8-rc5
> 
>  arch/arm64/kernel/hw_breakpoint.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index 35225632d70a..1ab9fc865ddd 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -301,28 +301,28 @@ static int get_hbp_len(u8 hbp_len)
>  
>  	switch (hbp_len) {
>  	case ARM_BREAKPOINT_LEN_1:
> -		len_in_bytes = 1;
> +		len_in_bytes = HW_BREAKPOINT_LEN_1;

I don't think we should do this. The HW_BREAKPOINT_LEN_* definitions are
part of the user ABI and, although they correspond to the length in bytes,
that's not necessarily something we should rely on.

Will