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Date:   Fri, 3 Nov 2017 10:53:08 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH 13/15] arm64: fix mrs_s/msr_s macros for clang LTO

These mrs_s and msr_s macros in particular were preventing us from
linking arm64 with Clang's integrated assembler, regardless of LTO.
Those macros ran into: https://bugs.llvm.org/show_bug.cgi?id=19749.
So while I appreciate how clever they are, they prevent us from
assembling with Clang so I would like to see them go.

On Fri, Nov 3, 2017 at 10:12 AM, Sami Tolvanen <samitolvanen@...gle.com> wrote:
> Clang's integrated assembler does not allow assembly macros defined
> in one inline asm block using the .macro directive to be used across
> separate asm blocks. LLVM developers consider this a feature and not a
> bug, recommending code refactoring:
>
>   https://bugs.llvm.org/show_bug.cgi?id=19749
>
> As binutils doesn't allow macros to be redefined, this change adds C
> preprocessor macros that define the assembly macros globally for binutils
> and locally for clang's integrated assembler.
>
> Suggested-by: Greg Hackmann <ghackmann@...gle.com>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_hyp.h |  2 ++
>  arch/arm64/include/asm/sysreg.h  | 71 ++++++++++++++++++++++++++++++----------
>  2 files changed, 56 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 4572a9b560fa..6840704ea894 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -29,6 +29,7 @@
>         ({                                                              \
>                 u64 reg;                                                \
>                 asm volatile(ALTERNATIVE("mrs %0, " __stringify(r##nvh),\
> +                                        DEFINE_MRS_S                   \
>                                          "mrs_s %0, " __stringify(r##vh),\
>                                          ARM64_HAS_VIRT_HOST_EXTN)      \
>                              : "=r" (reg));                             \
> @@ -39,6 +40,7 @@
>         do {                                                            \
>                 u64 __val = (u64)(v);                                   \
>                 asm volatile(ALTERNATIVE("msr " __stringify(r##nvh) ", %x0",\
> +                                        DEFINE_MSR_S                   \
>                                          "msr_s " __stringify(r##vh) ", %x0",\
>                                          ARM64_HAS_VIRT_HOST_EXTN)      \
>                                          : : "rZ" (__val));             \
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index f707fed5886f..1588ac3f3690 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -463,21 +463,58 @@
>
>  #include <linux/types.h>
>
> -asm(
> -"      .irp    num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30\n"
> -"      .equ    .L__reg_num_x\\num, \\num\n"
> -"      .endr\n"
> +#define ___MRS_MSR_S_REGNUM                                    \
> +"      .irp    num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30\n" \
> +"      .equ    .L__reg_num_x\\num, \\num\n"                    \
> +"      .endr\n"                                                \
>  "      .equ    .L__reg_num_xzr, 31\n"
> -"\n"
> -"      .macro  mrs_s, rt, sreg\n"
> -       __emit_inst(0xd5200000|(\\sreg)|(.L__reg_num_\\rt))
> +
> +#define ___MRS_S                                               \
> +"      .macro  mrs_s, rt, sreg\n"                              \
> +       __emit_inst(0xd5200000|(\\sreg)|(.L__reg_num_\\rt))     \
>  "      .endm\n"
> -"\n"
> -"      .macro  msr_s, sreg, rt\n"
> -       __emit_inst(0xd5000000|(\\sreg)|(.L__reg_num_\\rt))
> +
> +#define ___MSR_S                                               \
> +"      .macro  msr_s, sreg, rt\n"                              \
> +       __emit_inst(0xd5000000|(\\sreg)|(.L__reg_num_\\rt))     \
>  "      .endm\n"
> +
> +/*
> + * llvm-as doesn't allow macros defined in an asm block to be used in other
> + * asm blocks, which means we cannot define them globally.
> + */
> +#if !defined(CONFIG_CLANG_LTO)
> +asm(
> +       ___MRS_MSR_S_REGNUM
> +       ___MRS_S
> +       ___MSR_S
>  );
>
> +#undef  ___MRS_MSR_S_REGNUM
> +#define ___MRS_MSR_S_REGNUM
> +#undef  ___MRS_S
> +#define ___MRS_S
> +#undef  ___MSR_S
> +#define ___MSR_S
> +#endif
> +
> +#define DEFINE_MRS_S           \
> +       ___MRS_MSR_S_REGNUM     \
> +       ___MRS_S
> +
> +#define DEFINE_MSR_S           \
> +       ___MRS_MSR_S_REGNUM     \
> +       ___MSR_S
> +
> +
> +#define __mrs_s(r, v)                                          \
> +       DEFINE_MRS_S                                            \
> +"      mrs_s %0, " __stringify(r) : "=r" (v)
> +
> +#define __msr_s(r, v)                                          \
> +       DEFINE_MSR_S                                            \
> +"      msr_s " __stringify(r) ", %0" : : "r" (v)
> +
>  /*
>   * Unlike read_cpuid, calls to read_sysreg are never expected to be
>   * optimized away or replaced with synthetic values.
> @@ -502,15 +539,15 @@ asm(
>   * For registers without architectural names, or simply unsupported by
>   * GAS.
>   */
> -#define read_sysreg_s(r) ({                                            \
> -       u64 __val;                                                      \
> -       asm volatile("mrs_s %0, " __stringify(r) : "=r" (__val));       \
> -       __val;                                                          \
> +#define read_sysreg_s(r) ({                                    \
> +       u64 __val;                                              \
> +       asm volatile(__mrs_s(r, __val));                        \
> +       __val;                                                  \
>  })
>
> -#define write_sysreg_s(v, r) do {                                      \
> -       u64 __val = (u64)(v);                                           \
> -       asm volatile("msr_s " __stringify(r) ", %x0" : : "rZ" (__val)); \
> +#define write_sysreg_s(v, r) do {                              \
> +       u64 __val = (u64)(v);                                   \
> +       asm volatile(__msr_s(r, __val));                        \
>  } while (0)
>
>  static inline void config_sctlr_el1(u32 clear, u32 set)
> --
> 2.15.0.403.gc27cc4dac6-goog
>



-- 
Thanks,
~Nick Desaulniers

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