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authorNick Desaulniers2020-06-08 13:57:08 -0700
committerWill Deacon2020-06-10 11:38:56 +0100
commit625412c210fb6423e40cb22de7d14fc3bb9d9e79 (patch)
tree7f5fa74f4d10403f5964136687234a239f716898 /arch
parent961abd78adcb4c72c343fcd9f9dc5e2ebbe9b448 (diff)
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/Kconfig8
-rw-r--r--arch/arm64/kernel/vdso32/Makefile8
2 files changed, 16 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 77c440db9d46..63d711001dab 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1297,6 +1297,14 @@ config COMPAT_VDSO
You must have a 32-bit build of glibc 2.22 or later for programs
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
bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on SYSCTL
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 3964738ebbde..7ea1e827e505 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -105,6 +105,14 @@ VDSO_CFLAGS += -D__uint128_t='void*'
VDSO_CFLAGS += $(call cc32-disable-warning,shift-count-overflow)
VDSO_CFLAGS += -Wno-int-to-pointer-cast
+# Compile as THUMB2 or ARM. Unwinding via frame-pointers in THUMB2 is
+# unreliable.
+ifeq ($(CONFIG_THUMB2_COMPAT_VDSO), y)
+VDSO_CFLAGS += -mthumb -fomit-frame-pointer
+else
+VDSO_CFLAGS += -marm
+endif
+
VDSO_AFLAGS := $(VDSO_CAFLAGS)
VDSO_AFLAGS += -D__ASSEMBLY__