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From: Mark Brown <broonie@kernel.org>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Jeremy Linton <jeremy.linton@arm.com>,
	"H . J . Lu" <hjl.tools@gmail.com>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	libc-alpha@sourceware.org
Subject: Re: [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter
Date: Thu, 10 Jun 2021 14:19:05 +0100	[thread overview]
Message-ID: <YMIRSSMnP3UMwdRy@sirena.org.uk> (raw)
In-Reply-To: <20210609151713.GL4187@arm.com>

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On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote:
> On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote:

> > -		if (system_supports_bti() && has_interp == is_interp &&
> > -		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
> > -			arch->flags |= ARM64_ELF_BTI;
> > +		if (system_supports_bti() &&
> > +		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
> > +			if (is_interp) {
> > +				arch->flags |= ARM64_ELF_INTERP_BTI;
> > +			} else {
> > +				arch->flags |= ARM64_ELF_EXEC_BTI;
> > +			}

> Nit: surplus curlies? (coding-style.rst does actually say to drop them
> when all branches of an if are single-statement one-liners -- I had
> presumed I was just being pedantic...)

I really think this hurts readability with the nested if inside
another if with a multi-line condition.

> > -	if (prot & PROT_EXEC)
> > -		prot |= PROT_BTI;
> > +		if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp)
> > +			prot |= PROT_BTI;
> > +	}

> Is it worth adding () around the bitwise-& expressions?  I'm always a
> little uneasy about the operator precedence of binary &, although
> without looking it up I think you're correct.

Sure.  I'm fairly sure the compiler would've complained about
this case if it were ambiguous, I'm vaguely surprised it didn't
already.

> Feel free to adopt if this appeals to you, otherwise I'm also fine with
> your version.)

I'll see what I think when I get back to looking at this
properly.

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WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Jeremy Linton <jeremy.linton@arm.com>,
	"H . J . Lu" <hjl.tools@gmail.com>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	libc-alpha@sourceware.org
Subject: Re: [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter
Date: Thu, 10 Jun 2021 14:19:05 +0100	[thread overview]
Message-ID: <YMIRSSMnP3UMwdRy@sirena.org.uk> (raw)
In-Reply-To: <20210609151713.GL4187@arm.com>


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On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote:
> On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote:

> > -		if (system_supports_bti() && has_interp == is_interp &&
> > -		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
> > -			arch->flags |= ARM64_ELF_BTI;
> > +		if (system_supports_bti() &&
> > +		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
> > +			if (is_interp) {
> > +				arch->flags |= ARM64_ELF_INTERP_BTI;
> > +			} else {
> > +				arch->flags |= ARM64_ELF_EXEC_BTI;
> > +			}

> Nit: surplus curlies? (coding-style.rst does actually say to drop them
> when all branches of an if are single-statement one-liners -- I had
> presumed I was just being pedantic...)

I really think this hurts readability with the nested if inside
another if with a multi-line condition.

> > -	if (prot & PROT_EXEC)
> > -		prot |= PROT_BTI;
> > +		if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp)
> > +			prot |= PROT_BTI;
> > +	}

> Is it worth adding () around the bitwise-& expressions?  I'm always a
> little uneasy about the operator precedence of binary &, although
> without looking it up I think you're correct.

Sure.  I'm fairly sure the compiler would've complained about
this case if it were ambiguous, I'm vaguely surprised it didn't
already.

> Feel free to adopt if this appeals to you, otherwise I'm also fine with
> your version.)

I'll see what I think when I get back to looking at this
properly.

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_______________________________________________
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  reply	other threads:[~2021-06-10 13:54 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04 11:24 [PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter Mark Brown
2021-06-04 11:24 ` Mark Brown
2021-06-04 11:24 ` [PATCH v2 1/3] elf: Allow architectures to parse properties on the main executable Mark Brown
2021-06-04 11:24   ` Mark Brown
2021-06-09 15:16   ` Dave Martin
2021-06-09 15:16     ` Dave Martin
2021-06-10 13:41     ` Mark Brown
2021-06-10 13:41       ` Mark Brown
2021-06-04 11:24 ` [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter Mark Brown
2021-06-04 11:24   ` Mark Brown
2021-06-09 15:17   ` Dave Martin
2021-06-09 15:17     ` Dave Martin
2021-06-10 13:19     ` Mark Brown [this message]
2021-06-10 13:19       ` Mark Brown
2021-06-10 15:34       ` Dave Martin
2021-06-10 15:34         ` Dave Martin
2021-06-04 11:24 ` [PATCH v2 3/3] elf: Remove has_interp property from arch_adjust_elf_prot() Mark Brown
2021-06-04 11:24   ` Mark Brown
2021-06-09 15:17   ` Dave Martin
2021-06-09 15:17     ` Dave Martin
2021-06-09 16:55     ` Yu, Yu-cheng
2021-06-09 16:55       ` Yu, Yu-cheng
2021-06-10  9:58       ` Dave Martin
2021-06-10  9:58         ` Dave Martin
2021-06-10 18:17         ` Yu, Yu-cheng
2021-06-10 18:17           ` Yu, Yu-cheng
2021-06-10 13:34     ` Mark Brown
2021-06-10 13:34       ` Mark Brown
2021-06-10 15:40       ` Dave Martin
2021-06-10 15:40         ` Dave Martin
2021-06-10 16:28 ` [PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter Jeremy Linton
2021-06-10 16:28   ` Jeremy Linton
2021-06-14 16:00   ` Mark Brown
2021-06-14 16:00     ` Mark Brown
2021-06-15 15:22   ` Dave Martin
2021-06-15 15:22     ` Dave Martin
2021-06-15 15:33     ` Mark Brown
2021-06-15 15:33       ` Mark Brown
2021-06-15 15:41       ` Dave Martin
2021-06-15 15:41         ` Dave Martin
2021-06-16  5:12         ` Jeremy Linton
2021-06-16  5:12           ` Jeremy Linton

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