2021-01-07 12:37:45

by Alexander Lobakin

Subject: [PATCH v4 mips-next 3/7] MIPS: properly stop .eh_frame generation

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 <[email protected]>
Signed-off-by: Alexander Lobakin <[email protected]>
---
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

2021-01-07 21:52:38

by Kees Cook

Subject: Re: [PATCH v4 mips-next 3/7] MIPS: properly stop .eh_frame generation

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 <[email protected]>
> Signed-off-by: Alexander Lobakin <[email protected]>

Reviewed-by: Kees Cook <[email protected]>

--
Kees Cook

2021-01-08 21:18:52

by Nathan Chancellor

Subject: Re: [PATCH v4 mips-next 3/7] MIPS: properly stop .eh_frame generation

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 <[email protected]>
> Signed-off-by: Alexander Lobakin <[email protected]>

Reviewed-by: Nathan Chancellor <[email protected]>

> ---
> 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
>
>