Re: [Qemu-devel] [PATCH 08/11] tcg/aarch64: Make direct jump patching thread-safe

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 07/04/16 18:53, Sergey Fedorov wrote:
> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> Ensure direct jump patching in AArch64 is atomic by using
> atomic_read()/atomic_set() for code patching.
>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>  tcg/aarch64/tcg-target.inc.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
> index 0ed10a974121..15fdebec921f 100644
> --- a/tcg/aarch64/tcg-target.inc.c
> +++ b/tcg/aarch64/tcg-target.inc.c
> @@ -73,6 +73,18 @@ static inline void reloc_pc26(tcg_insn_unit *code_ptr, tcg_insn_unit *target)
>      *code_ptr = deposit32(*code_ptr, 0, 26, offset);
>  }
>  
> +static inline void reloc_pc26_atomic(tcg_insn_unit *code_ptr,
> +                                     tcg_insn_unit *target)
> +{
> +    ptrdiff_t offset = target - code_ptr;
> +    tcg_insn_unit insn;
> +    assert(offset == sextract64(offset, 0, 26));

I'd better use tcg_debug_assert() here as in this patch:

http://patchwork.ozlabs.org/patch/613020/

Kind regards,
Sergey

> +    /* read instruction, mask away previous PC_REL26 parameter contents,
> +       set the proper offset, then write back the instruction. */
> +    insn = atomic_read(code_ptr);
> +    atomic_set(code_ptr, deposit32(insn, 0, 26, offset));
> +}
> +
>  static inline void reloc_pc19(tcg_insn_unit *code_ptr, tcg_insn_unit *target)
>  {
>      ptrdiff_t offset = target - code_ptr;
> @@ -835,7 +847,7 @@ void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
>      tcg_insn_unit *code_ptr = (tcg_insn_unit *)jmp_addr;
>      tcg_insn_unit *target = (tcg_insn_unit *)addr;
>  
> -    reloc_pc26(code_ptr, target);
> +    reloc_pc26_atomic(code_ptr, target);
>      flush_icache_range(jmp_addr, jmp_addr + 4);
>  }
>