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arm64: vdso32: add CONFIG_THUMB2_COMPAT_VDSO 

Allow the compat vdso (32b) to be compiled as either THUMB2 (default) or
ARM.

For THUMB2, the register r7 is reserved for the frame pointer, but
code in arch/arm64/include/asm/vdso/compat_gettimeofday.h
uses r7. Explicitly set -fomit-frame-pointer, since unwinding through
interworked THUMB2 and ARM is unreliable anyways. See also how
CONFIG_UNWINDER_FRAME_POINTER cannot be selected for
CONFIG_THUMB2_KERNEL for ARCH=arm.

This also helps toolchains that differ in their implicit value if the
choice of -f{no-}omit-frame-pointer is left unspecified, to not error on
the use of r7.

2019 Q4 ARM AAPCS seeks to standardize the use of r11 as the reserved
frame pointer register, but no production compiler that can compile the
Linux kernel currently implements this.  We're actively discussing such
a transition with ARM toolchain developers currently.

Reported-by: Luis Lozano <llozano@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Manoj Gupta <manojgupta@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Stephen Boyd <swboyd@google.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Link: https://static.docs.arm.com/ihi0042/i/aapcs32.pdf
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1084372
Link: https://lore.kernel.org/r/20200608205711.109418-1-ndesaulniers@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Nick Desaulniers 2020-06-08 13:57:08 -07:00 committed by Will Deacon
parent 961abd78ad
commit 625412c210
2 changed files with 16 additions and 0 deletions
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8
arch/arm64/Kconfig
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@ -1297,6 +1297,14 @@ config COMPAT_VDSO
You must have a 32-bit build of glibc 2.22 or later for programs You must have a 32-bit build of glibc 2.22 or later for programs
to seamlessly take advantage of this. to seamlessly take advantage of this.
config THUMB2_COMPAT_VDSO
bool "Compile the 32-bit vDSO for Thumb-2 mode" if EXPERT
depends on COMPAT_VDSO
default y
help
Compile the compat vDSO with '-mthumb -fomit-frame-pointer' if y,
otherwise with '-marm'.
menuconfig ARMV8_DEPRECATED menuconfig ARMV8_DEPRECATED
bool "Emulate deprecated/obsolete ARMv8 instructions" bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on SYSCTL depends on SYSCTL

8
arch/arm64/kernel/vdso32/Makefile
View File

@ -105,6 +105,14 @@ VDSO_CFLAGS += -D__uint128_t='void*'
VDSO_CFLAGS += $(call cc32-disable-warning,shift-count-overflow) VDSO_CFLAGS += $(call cc32-disable-warning,shift-count-overflow)
VDSO_CFLAGS += -Wno-int-to-pointer-cast VDSO_CFLAGS += -Wno-int-to-pointer-cast
# Compile as THUMB2 or ARM. Unwinding via frame-pointers in THUMB2 is
# unreliable.
ifeq ($(CONFIG_THUMB2_COMPAT_VDSO), y)
VDSO_CFLAGS += -mthumb -fomit-frame-pointer
else
VDSO_CFLAGS += -marm
endif
VDSO_AFLAGS := $(VDSO_CAFLAGS) VDSO_AFLAGS := $(VDSO_CAFLAGS)
VDSO_AFLAGS += -D__ASSEMBLY__ VDSO_AFLAGS += -D__ASSEMBLY__