* [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags
@ 2020-04-29 15:10 Vincenzo Frascino
2020-04-30 10:48 ` Szabolcs Nagy
2020-04-30 17:39 ` Catalin Marinas
0 siblings, 2 replies; 3+ messages in thread
From: Vincenzo Frascino @ 2020-04-29 15:10 UTC (permalink / raw)
To: linux-arm-kernel
Cc: tamas.zsoldos, Catalin Marinas, Szabolcs Nagy, Vincenzo Frascino,
Will Deacon
On arm64 linux gcc uses -fasynchronous-unwind-tables -funwind-tables
by default since gcc-8, so now the de facto platform ABI is to allow
unwinding from async signal handlers.
However on bare metal targets (aarch64-none-elf), and on old gcc,
async and sync unwind tables are not enabled by default to avoid
runtime memory costs.
This means if linux is built with a baremetal toolchain the vdso.so
may not have unwind tables which breaks the gcc platform ABI guarantee
in userspace.
Add -fasynchronous-unwind-tables explicitly to the vgettimeofday.o
cflags to address the ABI change.
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
arch/arm64/kernel/vdso/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 77ee40f4c8b7..59555612fb1d 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -35,7 +35,7 @@ UBSAN_SANITIZE := n
OBJECT_FILES_NON_STANDARD := y
KCOV_INSTRUMENT := n
-CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
+CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables
ifneq ($(c-gettimeofday-y),)
CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
--
2.26.2
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags
2020-04-29 15:10 [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags Vincenzo Frascino
@ 2020-04-30 10:48 ` Szabolcs Nagy
2020-04-30 17:39 ` Catalin Marinas
1 sibling, 0 replies; 3+ messages in thread
From: Szabolcs Nagy @ 2020-04-30 10:48 UTC (permalink / raw)
To: Vincenzo Frascino
Cc: tamas.zsoldos, Catalin Marinas, Will Deacon, linux-arm-kernel
The 04/29/2020 16:10, Vincenzo Frascino wrote:
> On arm64 linux gcc uses -fasynchronous-unwind-tables -funwind-tables
> by default since gcc-8, so now the de facto platform ABI is to allow
> unwinding from async signal handlers.
>
> However on bare metal targets (aarch64-none-elf), and on old gcc,
> async and sync unwind tables are not enabled by default to avoid
> runtime memory costs.
>
> This means if linux is built with a baremetal toolchain the vdso.so
> may not have unwind tables which breaks the gcc platform ABI guarantee
> in userspace.
>
> Add -fasynchronous-unwind-tables explicitly to the vgettimeofday.o
> cflags to address the ABI change.
>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
thanks, the patch looks good to me.
> ---
> arch/arm64/kernel/vdso/Makefile | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index 77ee40f4c8b7..59555612fb1d 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -35,7 +35,7 @@ UBSAN_SANITIZE := n
> OBJECT_FILES_NON_STANDARD := y
> KCOV_INSTRUMENT := n
>
> -CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
> +CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables
>
> ifneq ($(c-gettimeofday-y),)
> CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> --
> 2.26.2
>
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags
2020-04-29 15:10 [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags Vincenzo Frascino
2020-04-30 10:48 ` Szabolcs Nagy
@ 2020-04-30 17:39 ` Catalin Marinas
1 sibling, 0 replies; 3+ messages in thread
From: Catalin Marinas @ 2020-04-30 17:39 UTC (permalink / raw)
To: Vincenzo Frascino
Cc: tamas.zsoldos, Szabolcs Nagy, Will Deacon, linux-arm-kernel
On Wed, Apr 29, 2020 at 04:10:50PM +0100, Vincenzo Frascino wrote:
> On arm64 linux gcc uses -fasynchronous-unwind-tables -funwind-tables
> by default since gcc-8, so now the de facto platform ABI is to allow
> unwinding from async signal handlers.
>
> However on bare metal targets (aarch64-none-elf), and on old gcc,
> async and sync unwind tables are not enabled by default to avoid
> runtime memory costs.
>
> This means if linux is built with a baremetal toolchain the vdso.so
> may not have unwind tables which breaks the gcc platform ABI guarantee
> in userspace.
>
> Add -fasynchronous-unwind-tables explicitly to the vgettimeofday.o
> cflags to address the ABI change.
>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Queued for 5.7. Thanks.
--
Catalin
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-04-29 15:10 [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags Vincenzo Frascino
2020-04-30 10:48 ` Szabolcs Nagy
2020-04-30 17:39 ` Catalin Marinas
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