On Thu, Jan 07, 2021 at 12:35:01PM +0000, Alexander Lobakin wrote:
> Commit 866b6a89c6d1 ("MIPS: Add DWARF unwinding to assembly") added
> -fno-asynchronous-unwind-tables to KBUILD_CFLAGS to prevent compiler
> from emitting .eh_frame symbols.
> However, as MIPS heavily uses CFI, that's not enough. Use the
> approach taken for x86 (as it also uses CFI) and explicitly put CFI
> symbols into the .debug_frame section (except for VDSO).
> This allows us to drop .eh_frame from DISCARDS as it's no longer
> being generated.
>
> Fixes: 866b6a89c6d1 ("MIPS: Add DWARF unwinding to assembly")
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> arch/mips/include/asm/asm.h | 18 ++++++++++++++++++
> arch/mips/kernel/vmlinux.lds.S | 1 -
> 2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/include/asm/asm.h b/arch/mips/include/asm/asm.h
> index 3682d1a0bb80..908f6d6ae24b 100644
> --- a/arch/mips/include/asm/asm.h
> +++ b/arch/mips/include/asm/asm.h
> @@ -20,10 +20,27 @@
> #include <asm/sgidefs.h>
> #include <asm/asm-eva.h>
>
> +#ifndef __VDSO__
> +/*
> + * Emit CFI data in .debug_frame sections, not .eh_frame sections.
> + * We don't do DWARF unwinding at runtime, so only the offline DWARF
> + * information is useful to anyone. Note we should change this if we
> + * ever decide to enable DWARF unwinding at runtime.
> + */
> +#define CFI_SECTIONS .cfi_sections .debug_frame
> +#else
> + /*
> + * For the vDSO, emit both runtime unwind information and debug
> + * symbols for the .dbg file.
> + */
> +#define CFI_SECTIONS
> +#endif
> +
> /*
> * LEAF - declare leaf routine
> */
> #define LEAF(symbol) \
> + CFI_SECTIONS; \
> .globl symbol; \
> .align 2; \
> .type symbol, @function; \
> @@ -36,6 +53,7 @@ symbol: .frame sp, 0, ra; \
> * NESTED - declare nested routine entry point
> */
> #define NESTED(symbol, framesize, rpc) \
> + CFI_SECTIONS; \
> .globl symbol; \
> .align 2; \
> .type symbol, @function; \
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index 16468957cba2..0f4e46ea4458 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -225,6 +225,5 @@ SECTIONS
> *(.options)
> *(.pdr)
> *(.reginfo)
> - *(.eh_frame)
> }
> }
> --
> 2.30.0
>
>
