[PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags

[PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags

[Vincenzo Frascino]

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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Re: [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags

[Szabolcs Nagy]

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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Re: [PATCH v2] arm64: vdso: Add -fasynchronous-unwind-tables to cflags

[Catalin Marinas]

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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