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From: Christoph Hellwig <hch@lst.de>
To: Heiko Stuebner <heiko@sntech.de>
Cc: palmer@dabbelt.com, paul.walmsley@sifive.com,
	aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, wefu@redhat.com,
	liush@allwinnertech.com, guoren@kernel.org,
	atishp@atishpatra.org, anup@brainfault.org, drew@beagleboard.org,
	hch@lst.de, arnd@arndb.de, wens@csie.org, maxime@cerno.tech,
	gfavor@ventanamicro.com, andrea.mondelli@huawei.com,
	behrensj@mit.edu, xinhaoqu@huawei.com, mick@ics.forth.gr,
	allen.baum@esperantotech.com, jscheid@ventanamicro.com,
	rtrauben@gmail.com, samuel@sholland.org, cmuellner@linux.com,
	philipp.tomsich@vrull.eu
Subject: Re: [PATCH v8 07/14] riscv: prevent compressed instructions in alternatives
Date: Thu, 31 Mar 2022 11:56:58 +0200	[thread overview]
Message-ID: <20220331095658.GD23422@lst.de> (raw)
In-Reply-To: <20220324000710.575331-8-heiko@sntech.de>

On Thu, Mar 24, 2022 at 01:07:03AM +0100, Heiko Stuebner wrote:
> Instructions are opportunistically compressed by the RISC-V assembler
> when possible, but in alternatives-blocks both the old and new content
> need to be the same size, so having the toolchain do somewhat random
> optimizations will cause strange side-effects like
> "attempt to move .org backwards" compile-time errors.
> 
> Already a simple "and" used in alternatives assembly will cause these
> mismatched code sizes.
> 
> So prevent compressed instructions to be generated in alternatives-
> code and use option-push and -pop to only limit this to the relevant
> code blocks

Yes, that makes sense:

Reviewed-by: Christoph Hellwig <hch@lst.de>

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WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Heiko Stuebner <heiko@sntech.de>
Cc: palmer@dabbelt.com, paul.walmsley@sifive.com,
	aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, wefu@redhat.com,
	liush@allwinnertech.com, guoren@kernel.org,
	atishp@atishpatra.org, anup@brainfault.org, drew@beagleboard.org,
	hch@lst.de, arnd@arndb.de, wens@csie.org, maxime@cerno.tech,
	gfavor@ventanamicro.com, andrea.mondelli@huawei.com,
	behrensj@mit.edu, xinhaoqu@huawei.com, mick@ics.forth.gr,
	allen.baum@esperantotech.com, jscheid@ventanamicro.com,
	rtrauben@gmail.com, samuel@sholland.org, cmuellner@linux.com,
	philipp.tomsich@vrull.eu
Subject: Re: [PATCH v8 07/14] riscv: prevent compressed instructions in alternatives
Date: Thu, 31 Mar 2022 11:56:58 +0200	[thread overview]
Message-ID: <20220331095658.GD23422@lst.de> (raw)
In-Reply-To: <20220324000710.575331-8-heiko@sntech.de>

On Thu, Mar 24, 2022 at 01:07:03AM +0100, Heiko Stuebner wrote:
> Instructions are opportunistically compressed by the RISC-V assembler
> when possible, but in alternatives-blocks both the old and new content
> need to be the same size, so having the toolchain do somewhat random
> optimizations will cause strange side-effects like
> "attempt to move .org backwards" compile-time errors.
> 
> Already a simple "and" used in alternatives assembly will cause these
> mismatched code sizes.
> 
> So prevent compressed instructions to be generated in alternatives-
> code and use option-push and -pop to only limit this to the relevant
> code blocks

Yes, that makes sense:

Reviewed-by: Christoph Hellwig <hch@lst.de>

  reply	other threads:[~2022-03-31  9:57 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-24  0:06 [PATCH v8 00/14] riscv: support for Svpbmt and D1 memory types Heiko Stuebner
2022-03-24  0:06 ` Heiko Stuebner
2022-03-24  0:06 ` [PATCH v8 01/14] riscv: prevent null-pointer dereference with sbi_remote_fence_i Heiko Stuebner
2022-03-24  0:06   ` Heiko Stuebner
2022-03-31  9:51   ` Christoph Hellwig
2022-03-31  9:51     ` Christoph Hellwig
2022-03-31 12:28     ` Heiko Stübner
2022-03-31 12:28       ` Heiko Stübner
2022-03-31 12:33       ` Christoph Hellwig
2022-03-31 12:33         ` Christoph Hellwig
2022-04-07 18:50         ` Heiko Stübner
2022-04-07 18:50           ` Heiko Stübner
2022-03-24  0:06 ` [PATCH v8 02/14] riscv: integrate alternatives better into the main architecture Heiko Stuebner
2022-03-24  0:06   ` Heiko Stuebner
2022-03-31  9:53   ` Christoph Hellwig
2022-03-31  9:53     ` Christoph Hellwig
2022-03-24  0:06 ` [PATCH v8 03/14] riscv: allow different stages with alternatives Heiko Stuebner
2022-03-24  0:06   ` Heiko Stuebner
2022-03-24  0:07 ` [PATCH v8 04/14] riscv: implement module alternatives Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-24  0:07 ` [PATCH v8 05/14] riscv: implement ALTERNATIVE_2 macro Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31  9:56   ` Christoph Hellwig
2022-03-31  9:56     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 06/14] riscv: extend concatenated alternatives-lines to the same length Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-24  0:07 ` [PATCH v8 07/14] riscv: prevent compressed instructions in alternatives Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31  9:56   ` Christoph Hellwig [this message]
2022-03-31  9:56     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 08/14] riscv: move boot alternatives to after fill_hwcap Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31  9:57   ` Christoph Hellwig
2022-03-31  9:57     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 09/14] riscv: Fix accessing pfn bits in PTEs for non-32bit variants Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31  9:59   ` Christoph Hellwig
2022-03-31  9:59     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 10/14] riscv: add cpufeature handling via alternatives Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31 10:01   ` Christoph Hellwig
2022-03-31 10:01     ` Christoph Hellwig
2022-04-08 16:13     ` Heiko Stübner
2022-04-08 16:13       ` Heiko Stübner
2022-03-24  0:07 ` [PATCH v8 11/14] riscv: add RISC-V Svpbmt extension support Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31 10:03   ` Christoph Hellwig
2022-03-31 10:03     ` Christoph Hellwig
2022-03-31 12:19     ` Heiko Stübner
2022-03-31 12:19       ` Heiko Stübner
2022-03-31 12:27       ` Christoph Hellwig
2022-03-31 12:27         ` Christoph Hellwig
2022-03-31 12:29   ` Christoph Hellwig
2022-03-31 12:29     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 12/14] riscv: remove FIXMAP_PAGE_IO and fall back to its default value Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31 10:03   ` Christoph Hellwig
2022-03-31 10:03     ` Christoph Hellwig
2022-03-24  0:07 ` [PATCH v8 13/14] riscv: don't use global static vars to store alternative data Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-24  0:07 ` [PATCH v8 14/14] riscv: add memory-type errata for T-Head Heiko Stuebner
2022-03-24  0:07   ` Heiko Stuebner
2022-03-31  2:24 ` [PATCH v8 00/14] riscv: support for Svpbmt and D1 memory types Palmer Dabbelt
2022-03-31  2:24   ` Palmer Dabbelt

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