All of lore.kernel.org
 help / color / mirror / Atom feed
From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk
Cc: Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Kees Cook <keescook@chromium.org>,
	Keith Packard <keithpac@amazon.com>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: [PATCH v2 2/9] ARM: assembler: introduce bl_r and bl_m macros
Date: Tue,  5 Oct 2021 09:15:35 +0200	[thread overview]
Message-ID: <20211005071542.3127341-3-ardb@kernel.org> (raw)
In-Reply-To: <20211005071542.3127341-1-ardb@kernel.org>

Add some macros that abstract the difference between the ways indirect
calls are performed on older and newer ARM architecture revisions.

The main difference is to prefer blx instructions over explicit LR
assignments when possible, as these tend to confuse the prediction logic
in out-of-order cores when speculating across a function return.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/assembler.h | 37 ++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 7d23d4bb2168..abb8202ef0da 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -624,4 +624,41 @@ THUMB(	orr	\reg , \reg , #PSR_T_BIT	)
 	.endif
 	.endm
 
+	/*
+	 * bl_r - branch and link to register
+	 *
+	 * @dst: target to branch to
+	 * @c: conditional opcode suffix
+	 */
+	.macro		bl_r, dst:req, c
+	.if		__LINUX_ARM_ARCH__ < 6
+	mov\c		lr, pc
+	mov\c		pc, \dst
+	.else
+	blx\c		\dst
+	.endif
+	.endm
+
+	/*
+	 * bl_m - branch and link to address held in memory
+	 *
+	 * @dst: memory reference to load the branch target from
+	 *
+	 * This uses the same syntax as ldr instructions, including things like
+	 * register writeback (where it makes sense). For example,
+	 *
+	 *    bl_m    [ip, #<offset>]
+	 *
+	 * Note that @dst should not reference lr as it may be clobbered early.
+	 */
+	.macro		bl_m, dst:vararg
+	.if		__LINUX_ARM_ARCH__ < 6
+	mov		lr, pc
+	ldr		pc, \dst
+	.else
+	ldr		lr, \dst
+	blx		lr
+	.endif
+	.endm
+
 #endif /* __ASM_ASSEMBLER_H__ */
-- 
2.30.2


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-10-05  7:18 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-05  7:15 [PATCH v2 0/9] ARM: add support for IRQ stacks Ard Biesheuvel
2021-10-05  7:15 ` [PATCH v2 1/9] ARM: remove some dead code Ard Biesheuvel
2021-10-05 12:06   ` Arnd Bergmann
2021-10-05  7:15 ` Ard Biesheuvel [this message]
2021-10-05 12:10   ` [PATCH v2 2/9] ARM: assembler: introduce bl_r and bl_m macros Arnd Bergmann
2021-10-05 12:14     ` Ard Biesheuvel
2021-10-05  7:15 ` [PATCH v2 3/9] ARM: optimize indirect call to handle_arch_irq for v7 cores Ard Biesheuvel
2021-10-05 12:11   ` Arnd Bergmann
2021-10-05  7:15 ` [PATCH v2 4/9] ARM: unwind: support unwinding across multiple stacks Ard Biesheuvel
2021-10-05 12:17   ` Arnd Bergmann
2021-10-05  7:15 ` [PATCH v2 5/9] ARM: export dump_mem() to other objects Ard Biesheuvel
2021-10-05 12:15   ` Arnd Bergmann
2021-10-05  7:15 ` [PATCH v2 6/9] ARM: unwind: dump exception stack from calling frame Ard Biesheuvel
2021-10-05 12:20   ` Arnd Bergmann
2021-10-05  7:15 ` [PATCH v2 7/9] ARM: implement IRQ stacks Ard Biesheuvel
2021-10-05 12:26   ` Arnd Bergmann
2021-10-05  7:15 ` [PATCH v2 8/9] ARM: call_with_stack: add unwind support Ard Biesheuvel
2021-10-05 12:22   ` Arnd Bergmann
2021-10-05 18:46     ` Nick Desaulniers
2021-10-05 18:46       ` Nick Desaulniers
2021-10-05 18:57       ` Ard Biesheuvel
2021-10-05 18:57         ` Ard Biesheuvel
2021-10-05  7:15 ` [PATCH v2 9/9] ARM: run softirqs on the per-CPU IRQ stack Ard Biesheuvel
2021-10-05 12:23   ` Arnd Bergmann
2021-10-06 15:21     ` Ard Biesheuvel
2021-10-11 23:29 ` [PATCH v2 0/9] ARM: add support for IRQ stacks Keith Packard
2021-10-16 22:04 ` Linus Walleij

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211005071542.3127341-3-ardb@kernel.org \
    --to=ardb@kernel.org \
    --cc=arnd@arndb.de \
    --cc=keescook@chromium.org \
    --cc=keithpac@amazon.com \
    --cc=linus.walleij@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux@armlinux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.