> -----Original Message-----
> From: Szabolcs Nagy <szabolcs.n...@arm.com>
> Sent: 08 July 2020 17:28
> To: gcc-patches@gcc.gnu.org
> Cc: Richard Earnshaw <richard.earns...@arm.com>; Kyrylo Tkachov
> <kyrylo.tkac...@arm.com>
> Subject: [PATCH 5/6] aarch64: Fix BTI support in libgcc
>
> lse.S did not have the GNU property note markup and the BTI c
> instructions that are necessary when it is built with branch
> protection.
>
> The notes are only added when libgcc is built with branch
> protection, because old linkers mishandle the note (merge
> them incorrectly or emit warnings), the BTI instructions
> are added unconditionally.
>
> Note: BTI c is only necessary at function entry if the function
> may be called indirectly, currently lse functions are not called
> indirectly, but BTI is added for ABI reasons e.g. to allow
> linkers later to emit stub code with indirect jump.
>
Ok.
Thanks,
Kyrill
> libgcc/ChangeLog:
>
> 2020-07-08 Szabolcs Nagy <szabolcs.n...@arm.com>
>
> * config/aarch64/lse.S: Add BTI marking and related definitions,
> and add BTI c to function entries.
> ---
> libgcc/config/aarch64/lse.S | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/libgcc/config/aarch64/lse.S b/libgcc/config/aarch64/lse.S
> index 9e2acae806b..64691c601c1 100644
> --- a/libgcc/config/aarch64/lse.S
> +++ b/libgcc/config/aarch64/lse.S
> @@ -136,6 +136,8 @@ see the files COPYING3 and COPYING.RUNTIME
> respectively. If not, see
> #define tmp1 17
> #define tmp2 15
>
> +#define BTI_C hint 34
> +
> /* Start and end a function. */
> .macro STARTFN name
> .text
> @@ -145,6 +147,7 @@ see the files COPYING3 and COPYING.RUNTIME
> respectively. If not, see
> .type \name, %function
> .cfi_startproc
> \name:
> + BTI_C
> .endm
>
> .macro ENDFN name
> @@ -275,6 +278,29 @@ STARTFN NAME(LDNM)
> ENDFN NAME(LDNM)
> #endif
>
> +/* GNU_PROPERTY_AARCH64_* macros from elf.h for use in asm code. */
> +#define FEATURE_1_AND 0xc0000000
> +#define FEATURE_1_BTI 1
> +#define FEATURE_1_PAC 2
> +
> +/* Add a NT_GNU_PROPERTY_TYPE_0 note. */
> +#define GNU_PROPERTY(type, value) \
> + .section .note.gnu.property, "a"; \
> + .p2align 3; \
> + .word 4; \
> + .word 16; \
> + .word 5; \
> + .asciz "GNU"; \
> + .word type; \
> + .word 4; \
> + .word value; \
> + .word 0;
> +
> #if defined(__linux__) || defined(__FreeBSD__)
> .section .note.GNU-stack, "", %progbits
> +
> +/* Add GNU property note if built with branch protection. */
> +# ifdef __ARM_FEATURE_BTI_DEFAULT
> +GNU_PROPERTY (FEATURE_1_AND, FEATURE_1_BTI)
> +# endif
> #endif
> --
> 2.17.1
