Re: [Qemu-devel] [PATCH v2 1/7] exec: Reorganize the GETRA/GETPC macros

[Aurelien Jarno <aurelien@aurel32.net>]

On Thu, Aug 29, 2013 at 03:05:55PM -0700, Richard Henderson wrote:
> Always define GETRA; use __builtin_extract_return_addr, rather than
> having a special case for s390.  Split GETPC_ADJ out of GETPC; use 2
> universally, rather than having a special case for arm.
> 
> Rename GETPC_LDST to GETRA_LDST to indicate that it does not
> contain the GETPC_ADJ value.  Likewise with GETPC_EXT to GETRA_EXT.
> 
> Perform the GETPC_ADJ adjustment inside helper_ret_ld/st.  This will
> allow backends to pass along the "true" return address rather than
> the massaged GETPC value.  In the meantime, double application of
> GETPC_ADJ does not hurt, since the call insn in all ISAs is at least
> 4 bytes long.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  include/exec/exec-all.h         | 84 +++++++++++++++++++----------------------
>  include/exec/softmmu_template.h | 24 ++++++++----
>  2 files changed, 56 insertions(+), 52 deletions(-)
> 
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index ffb69a4..6f71a4f 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -295,47 +295,42 @@ static inline void tb_add_jump(TranslationBlock *tb, int n,
>      }
>  }
>  
> -/* The return address may point to the start of the next instruction.
> -   Subtracting one gets us the call instruction itself.  */
> +/* GETRA is the true target of the return instruction that we'll execute,
> +   defined here for simplicity of defining the follow-up macros.  */
>  #if defined(CONFIG_TCG_INTERPRETER)
>  extern uintptr_t tci_tb_ptr;
> -# define GETPC() tci_tb_ptr
> -#elif defined(__s390__) && !defined(__s390x__)
> -# define GETPC() \
> -    (((uintptr_t)__builtin_return_address(0) & 0x7fffffffUL) - 1)
> -#elif defined(__arm__)
> -/* Thumb return addresses have the low bit set, so we need to subtract two.
> -   This is still safe in ARM mode because instructions are 4 bytes.  */
> -# define GETPC() ((uintptr_t)__builtin_return_address(0) - 2)
> +# define GETRA() tci_tb_ptr
> +#else
> +# define GETRA() \
> +    ((uintptr_t)__builtin_extract_return_addr(__builtin_return_address(0)))
> +#endif
> +
> +/* The true return address will often point to a host insn that is part of
> +   the next translated guest insn.  Adjust the address backward to point to
> +   the middle of the call insn.  Subtracting one would do the job except for
> +   several compressed mode architectures (arm, mips) which set the low bit
> +   to indicate the compressed mode; subtracting two works around that.  It
> +   is also the case that there are no host isas that contain a call insn
> +   smaller than 4 bytes, so we don't worry about special-casing this.  */
> +#if defined(CONFIG_TCG_INTERPRETER)
> +# define GETPC_ADJ   0
>  #else
> -# define GETPC() ((uintptr_t)__builtin_return_address(0) - 1)
> +# define GETPC_ADJ   2
>  #endif
>  
> +#define GETPC()  (GETRA() - GETPC_ADJ)
> +
> +/* The LDST optimizations splits code generation into fast and slow path.
> +   In some implementations, we pass the "logical" return address manually;
> +   in others, we must infer the logical return from the true return.  */
>  #if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
> -/* qemu_ld/st optimization split code generation to fast and slow path, thus,
> -   it needs special handling for an MMU helper which is called from the slow
> -   path, to get the fast path's pc without any additional argument.
> -   It uses a tricky solution which embeds the fast path pc into the slow path.
> -
> -   Code flow in slow path:
> -   (1) pre-process
> -   (2) call MMU helper
> -   (3) jump to (5)
> -   (4) fast path information (implementation specific)
> -   (5) post-process (e.g. stack adjust)
> -   (6) jump to corresponding code of the next of fast path
> - */
> -# if defined(__i386__) || defined(__x86_64__)
> -#  define GETPC_EXT()  GETPC()
> -# elif defined (_ARCH_PPC) && !defined (_ARCH_PPC64)
> -#  define GETRA() ((uintptr_t)__builtin_return_address(0))
> -#  define GETPC_LDST() ((uintptr_t) ((*(int32_t *)(GETRA() - 4)) - 1))
> +# if defined (_ARCH_PPC) && !defined (_ARCH_PPC64)
> +#  define GETRA_LDST(RA)   (*(int32_t *)((RA) - 4))
>  # elif defined(__arm__)
>  /* We define two insns between the return address and the branch back to
>     straight-line.  Find and decode that branch insn.  */
> -#  define GETRA()       ((uintptr_t)__builtin_return_address(0))
> -#  define GETPC_LDST()  tcg_getpc_ldst(GETRA())
> -static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
> +#  define GETRA_LDST(RA)   tcg_getra_ldst(RA)
> +static inline uintptr_t tcg_getra_ldst(uintptr_t ra)
>  {
>      int32_t b;
>      ra += 8;                    /* skip the two insns */
> @@ -343,33 +338,32 @@ static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
>      b = (b << 8) >> (8 - 2);    /* extract the displacement */
>      ra += 8;                    /* branches are relative to pc+8 */
>      ra += b;                    /* apply the displacement */
> -    ra -= 4;                    /* return a pointer into the current opcode,
> -                                   not the start of the next opcode  */
>      return ra;
>  }
>  # elif defined(__aarch64__)
> -#  define GETRA()       ((uintptr_t)__builtin_return_address(0))
> -#  define GETPC_LDST()  tcg_getpc_ldst(GETRA())
> -static inline uintptr_t tcg_getpc_ldst(uintptr_t ra)
> +#  define GETRA_LDST(RA)  tcg_getra_ldst(RA)
> +static inline uintptr_t tcg_getra_ldst(uintptr_t ra)
>  {
>      int32_t b;
>      ra += 4;                    /* skip one instruction */
>      b = *(int32_t *)ra;         /* load the branch insn */
>      b = (b << 6) >> (6 - 2);    /* extract the displacement */
>      ra += b;                    /* apply the displacement  */
> -    ra -= 4;                    /* return a pointer into the current opcode,
> -                                   not the start of the next opcode  */
>      return ra;
>  }
> -# else
> -#  error "CONFIG_QEMU_LDST_OPTIMIZATION needs GETPC_LDST() implementation!"
>  # endif
> +#endif /* CONFIG_QEMU_LDST_OPTIMIZATION */
> +
> +/* ??? Delete these once they are no longer used.  */
>  bool is_tcg_gen_code(uintptr_t pc_ptr);
> -# ifndef GETPC_EXT
> -#  define GETPC_EXT() (is_tcg_gen_code(GETRA()) ? GETPC_LDST() : GETPC())
> -# endif
> +#ifdef GETRA_LDST
> +# define GETRA_EXT()  tcg_getra_ext(GETRA())
> +static inline uintptr_t tcg_getra_ext(uintptr_t ra)
> +{
> +    return is_tcg_gen_code(ra) ? GETRA_LDST(ra) : ra;
> +}
>  #else
> -# define GETPC_EXT() GETPC()
> +# define GETRA_EXT()  GETRA()
>  #endif
>  
>  #if !defined(CONFIG_USER_ONLY)
> diff --git a/include/exec/softmmu_template.h b/include/exec/softmmu_template.h
> index eaca9e1..2fc6ea3 100644
> --- a/include/exec/softmmu_template.h
> +++ b/include/exec/softmmu_template.h
> @@ -86,6 +86,9 @@ glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)(CPUArchState *env,
>      target_ulong tlb_addr = env->tlb_table[mmu_idx][index].ADDR_READ;
>      uintptr_t haddr;
>  
> +    /* Adjust the given return address.  */
> +    retaddr -= GETPC_ADJ;
> +
>      /* If the TLB entry is for a different page, reload and try again.  */
>      if ((addr & TARGET_PAGE_MASK)
>           != (tlb_addr & (TARGET_PAGE_MASK | TLB_INVALID_MASK))) {
> @@ -121,10 +124,12 @@ glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)(CPUArchState *env,
>  #endif
>          addr1 = addr & ~(DATA_SIZE - 1);
>          addr2 = addr1 + DATA_SIZE;
> -        res1 = glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)(env, addr1,
> -                                                            mmu_idx, retaddr);
> -        res2 = glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)(env, addr2,
> -                                                            mmu_idx, retaddr);
> +        /* Note the adjustment at the beginning of the function.
> +           Undo that for the recursion.  */
> +        res1 = glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)
> +            (env, addr1, mmu_idx, retaddr + GETPC_ADJ);
> +        res2 = glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)
> +            (env, addr2, mmu_idx, retaddr + GETPC_ADJ);
>          shift = (addr & (DATA_SIZE - 1)) * 8;
>  #ifdef TARGET_WORDS_BIGENDIAN
>          res = (res1 << shift) | (res2 >> ((DATA_SIZE * 8) - shift));
> @@ -150,7 +155,7 @@ glue(glue(helper_ld, SUFFIX), MMUSUFFIX)(CPUArchState *env, target_ulong addr,
>                                           int mmu_idx)
>  {
>      return glue(glue(helper_ret_ld, SUFFIX), MMUSUFFIX)(env, addr, mmu_idx,
> -                                                        GETPC_EXT());
> +                                                        GETRA_EXT());
>  }
>  
>  #ifndef SOFTMMU_CODE_ACCESS
> @@ -182,6 +187,9 @@ glue(glue(helper_ret_st, SUFFIX), MMUSUFFIX)(CPUArchState *env,
>      target_ulong tlb_addr = env->tlb_table[mmu_idx][index].addr_write;
>      uintptr_t haddr;
>  
> +    /* Adjust the given return address.  */
> +    retaddr -= GETPC_ADJ;
> +
>      /* If the TLB entry is for a different page, reload and try again.  */
>      if ((addr & TARGET_PAGE_MASK)
>          != (tlb_addr & (TARGET_PAGE_MASK | TLB_INVALID_MASK))) {
> @@ -223,8 +231,10 @@ glue(glue(helper_ret_st, SUFFIX), MMUSUFFIX)(CPUArchState *env,
>  #else
>              uint8_t val8 = val >> (i * 8);
>  #endif
> +            /* Note the adjustment at the beginning of the function.
> +               Undo that for the recursion.  */
>              glue(helper_ret_stb, MMUSUFFIX)(env, addr + i, val8,
> -                                            mmu_idx, retaddr);
> +                                            mmu_idx, retaddr + GETPC_ADJ);
>          }
>          return;
>      }
> @@ -245,7 +255,7 @@ glue(glue(helper_st, SUFFIX), MMUSUFFIX)(CPUArchState *env, target_ulong addr,
>                                           DATA_TYPE val, int mmu_idx)
>  {
>      glue(glue(helper_ret_st, SUFFIX), MMUSUFFIX)(env, addr, val, mmu_idx,
> -                                                 GETPC_EXT());
> +                                                 GETRA_EXT());
>  }
>  
>  #endif /* !defined(SOFTMMU_CODE_ACCESS) */

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net