From: Arnd Bergmann <arnd@kernel.org>
To: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Ard Biesheuvel <ardb@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
llvm@lists.linux.dev
Subject: [PATCH 06/14] ARM: disallow CONFIG_THUMB with ARMv4
Date: Tue, 28 Sep 2021 17:41:35 +0200 [thread overview]
Message-ID: <20210928154143.2106903-7-arnd@kernel.org> (raw)
In-Reply-To: <20210928154143.2106903-1-arnd@kernel.org>
From: Arnd Bergmann <arnd@arndb.de>
We can currently build a multi-cpu enabled kernel that allows both ARMv4
and ARMv5 CPUs, and also supports THUMB mode in user space.
However, returning to user space in this configuration with the usr_ret
macro requires the use of the 'bx' instruction, which is refused by
the assembler:
arch/arm/kernel/entry-armv.S: Assembler messages:
arch/arm/kernel/entry-armv.S:937: Error: selected processor does not support `bx lr' in ARM mode
arch/arm/kernel/entry-armv.S:960: Error: selected processor does not support `bx lr' in ARM mode
arch/arm/kernel/entry-armv.S:1003: Error: selected processor does not support `bx lr' in ARM mode
<instantiation>:2:2: note: instruction requires: armv4t
bx lr
While it would be possible to handle this correctly in principle, doing so
seems to not be worth it, if we can simply avoid the problem by enforcing
that a kernel supporting both ARMv4 and a later CPU architecture cannot
run THUMB binaries.
This turned up while build-testing with clang; for some reason,
gcc never triggered the problem.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/arm/mm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 82aa990c4180..58afba346729 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -675,7 +675,7 @@ config ARM_PV_FIXUP
config ARM_THUMB
bool "Support Thumb user binaries" if !CPU_THUMBONLY && EXPERT
- depends on CPU_THUMB_CAPABLE
+ depends on CPU_THUMB_CAPABLE && !CPU_32v4
default y
help
Say Y if you want to include kernel support for running user space
--
2.29.2
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@kernel.org>
To: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Ard Biesheuvel <ardb@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
llvm@lists.linux.dev
Subject: [PATCH 06/14] ARM: disallow CONFIG_THUMB with ARMv4
Date: Tue, 28 Sep 2021 17:41:35 +0200 [thread overview]
Message-ID: <20210928154143.2106903-7-arnd@kernel.org> (raw)
In-Reply-To: <20210928154143.2106903-1-arnd@kernel.org>
From: Arnd Bergmann <arnd@arndb.de>
We can currently build a multi-cpu enabled kernel that allows both ARMv4
and ARMv5 CPUs, and also supports THUMB mode in user space.
However, returning to user space in this configuration with the usr_ret
macro requires the use of the 'bx' instruction, which is refused by
the assembler:
arch/arm/kernel/entry-armv.S: Assembler messages:
arch/arm/kernel/entry-armv.S:937: Error: selected processor does not support `bx lr' in ARM mode
arch/arm/kernel/entry-armv.S:960: Error: selected processor does not support `bx lr' in ARM mode
arch/arm/kernel/entry-armv.S:1003: Error: selected processor does not support `bx lr' in ARM mode
<instantiation>:2:2: note: instruction requires: armv4t
bx lr
While it would be possible to handle this correctly in principle, doing so
seems to not be worth it, if we can simply avoid the problem by enforcing
that a kernel supporting both ARMv4 and a later CPU architecture cannot
run THUMB binaries.
This turned up while build-testing with clang; for some reason,
gcc never triggered the problem.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/arm/mm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 82aa990c4180..58afba346729 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -675,7 +675,7 @@ config ARM_PV_FIXUP
config ARM_THUMB
bool "Support Thumb user binaries" if !CPU_THUMBONLY && EXPERT
- depends on CPU_THUMB_CAPABLE
+ depends on CPU_THUMB_CAPABLE && !CPU_32v4
default y
help
Say Y if you want to include kernel support for running user space
--
2.29.2
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next prev parent reply other threads:[~2021-09-28 15:42 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-28 15:41 [PATCH 00/14] ARM: randconfig build fixes Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 01/14] ARM: RiscPC needs older gcc version Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 16:03 ` Arnd Bergmann
2021-09-28 16:03 ` Arnd Bergmann
2021-09-28 16:03 ` Arnd Bergmann
2021-09-29 8:45 ` Arnd Bergmann
2021-09-29 8:45 ` Arnd Bergmann
2021-09-29 8:45 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 02/14] ARM: patch: fix BE32 compilation Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 21:33 ` Linus Walleij
2021-09-28 21:33 ` Linus Walleij
2021-09-28 21:33 ` Linus Walleij
2021-09-28 15:41 ` [PATCH 03/14] ARM: remove duplicate memcpy() definition Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 21:39 ` Linus Walleij
2021-09-28 21:39 ` Linus Walleij
2021-09-28 21:39 ` Linus Walleij
2021-09-28 15:41 ` [PATCH 04/14] ARM: kprobes: address gcc -Wempty-body warning Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 05/14] ARM: ARMv7-M uses BE-8, not BE-32 Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann [this message]
2021-09-28 15:41 ` [PATCH 06/14] ARM: disallow CONFIG_THUMB with ARMv4 Arnd Bergmann
2021-09-29 18:52 ` Nick Desaulniers
2021-09-29 18:52 ` Nick Desaulniers
2021-09-29 18:52 ` Nick Desaulniers
2021-10-06 16:01 ` Ard Biesheuvel
2021-10-06 16:01 ` Ard Biesheuvel
2021-09-28 15:41 ` [PATCH 07/14] ARM: fix link warning with XIP + frame-pointer Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 08/14] ARM: kprobes: fix arch_init_kprobes() prototype Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 09/14] ARM: allow compile-testing without machine record Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 10/14] ARM: only warn about XIP address when not compile testing Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 11/14] ARM: kasan: work around LPAE build warning Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 12/14] ARM: add CONFIG_PHYS_OFFSET default values Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 16:02 ` Nicolas Pitre
2021-09-28 16:02 ` Nicolas Pitre
2021-09-28 16:02 ` Nicolas Pitre
2021-09-28 21:44 ` Linus Walleij
2021-09-28 21:44 ` Linus Walleij
2021-09-28 21:44 ` Linus Walleij
2021-09-28 15:41 ` [PATCH 13/14] ARM: use .arch directives instead of assembler command line flags Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 17:10 ` Nick Desaulniers
2021-09-28 17:10 ` Nick Desaulniers
2021-09-28 17:10 ` Nick Desaulniers
2021-09-28 18:32 ` Arnd Bergmann
2021-09-28 18:32 ` Arnd Bergmann
2021-09-28 18:32 ` Arnd Bergmann
2021-09-29 18:11 ` Nick Desaulniers
2021-09-29 18:11 ` Nick Desaulniers
2021-09-29 18:11 ` Nick Desaulniers
2022-01-21 22:17 ` Nathan Chancellor
2022-01-21 22:17 ` Nathan Chancellor
2021-09-28 15:41 ` [PATCH 14/14] [RFC] ARM: forbid ftrace with clang and thumb2_kernel Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 17:20 ` Nick Desaulniers
2021-09-28 17:20 ` Nick Desaulniers
2021-09-28 17:20 ` Nick Desaulniers
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