Re: [Qemu-devel] [PATCH v5 01/19] tcg-arm: Fix local stack frame

[Aurelien Jarno]

On Sun, Mar 31, 2013 at 03:34:47PM -0700, Richard Henderson wrote:
> We were not allocating TCG_STATIC_CALL_ARGS_SIZE, so this meant that
> any helper with more than 4 arguments would clobber the saved regs.
> Realizing that we're supposed to have this memory pre-allocated means
> we can clean up the tcg_out_arg functions, which were trying to do
> more stack allocation.
> 
> Allocate stack memory for the TCG temporaries while we're at it.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  tcg/arm/tcg-target.c | 120 
> ++++++++++++++++++++-------------------------------
>  1 file changed, 46 insertions(+), 74 deletions(-)
> 
> diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
> index 94c6ca4..d099b68 100644
> --- a/tcg/arm/tcg-target.c
> +++ b/tcg/arm/tcg-target.c
> @@ -1017,64 +1017,35 @@ static const void * const qemu_st_helpers[4] = {
>   * argreg is where we want to put this argument, arg is the argument itself.
>   * Return value is the updated argreg ready for the next call.
>   * Note that argreg 0..3 is real registers, 4+ on stack.
> - * When we reach the first stacked argument, we allocate space for it
> - * and the following stacked arguments using "str r8, [sp, #-0x10]!".
> - * Following arguments are filled in with "str r8, [sp, #0xNN]".
> - * For more than 4 stacked arguments we'd need to know how much
> - * space to allocate when we pushed the first stacked argument.
> - * We don't need this, so don't implement it (and will assert if you try it.)
>   *
>   * We provide routines for arguments which are: immediate, 32 bit
>   * value in register, 16 and 8 bit values in register (which must be zero
>   * extended before use) and 64 bit value in a lo:hi register pair.
>   */
> -#define DEFINE_TCG_OUT_ARG(NAME, ARGPARAM)                                 \
> -    static TCGReg NAME(TCGContext *s, TCGReg argreg, ARGPARAM)             \
> -    {                                                                      \
> -        if (argreg < 4) {                                                  \
> -            TCG_OUT_ARG_GET_ARG(argreg);                                   \
> -        } else if (argreg == 4) {                                          \
> -            TCG_OUT_ARG_GET_ARG(TCG_REG_R8);                               \
> -            tcg_out32(s, (COND_AL << 28) | 0x052d8010);                    \
> -        } else {                                                           \
> -            assert(argreg < 8);                                            \
> -            TCG_OUT_ARG_GET_ARG(TCG_REG_R8);                               \
> -            tcg_out32(s, (COND_AL << 28) | 0x058d8000 | (argreg - 4) * 4); \
> -        }                                                                  \
> -        return argreg + 1;                                                 \
> -    }
> -
> -#define TCG_OUT_ARG_GET_ARG(A) tcg_out_dat_imm(s, COND_AL, ARITH_MOV, A, 0, 
> arg)
> -DEFINE_TCG_OUT_ARG(tcg_out_arg_imm32, uint32_t arg)
> -#undef TCG_OUT_ARG_GET_ARG
> -#define TCG_OUT_ARG_GET_ARG(A) tcg_out_ext8u(s, COND_AL, A, arg)
> -DEFINE_TCG_OUT_ARG(tcg_out_arg_reg8, TCGReg arg)
> -#undef TCG_OUT_ARG_GET_ARG
> -#define TCG_OUT_ARG_GET_ARG(A) tcg_out_ext16u(s, COND_AL, A, arg)
> -DEFINE_TCG_OUT_ARG(tcg_out_arg_reg16, TCGReg arg)
> -#undef TCG_OUT_ARG_GET_ARG
> -
> -/* We don't use the macro for this one to avoid an unnecessary reg-reg
> - * move when storing to the stack.
> - */
> -static TCGReg tcg_out_arg_reg32(TCGContext *s, TCGReg argreg, TCGReg arg)
> -{
> -    if (argreg < 4) {
> -        tcg_out_mov_reg(s, COND_AL, argreg, arg);
> -    } else if (argreg == 4) {
> -        /* str arg, [sp, #-0x10]! */
> -        tcg_out32(s, (COND_AL << 28) | 0x052d0010 | (arg << 12));
> -    } else {
> -        assert(argreg < 8);
> -        /* str arg, [sp, #0xNN] */
> -        tcg_out32(s, (COND_AL << 28) | 0x058d0000 |
> -                  (arg << 12) | (argreg - 4) * 4);
> -    }
> -    return argreg + 1;
> -}
> -
> -static inline TCGReg tcg_out_arg_reg64(TCGContext *s, TCGReg argreg,
> -                                       TCGReg arglo, TCGReg arghi)
> +#define DEFINE_TCG_OUT_ARG(NAME, ARGTYPE, MOV_ARG, EXT_ARG)                \
> +static TCGReg NAME(TCGContext *s, TCGReg argreg, ARGTYPE arg)              \
> +{                                                                          \
> +    if (argreg < 4) {                                                      \
> +        MOV_ARG(s, COND_AL, argreg, arg);                                  \
> +    } else {                                                               \
> +        int ofs = (argreg - 4) * 4;                                        \
> +        EXT_ARG;                                                           \
> +        assert(ofs + 4 <= TCG_STATIC_CALL_ARGS_SIZE);                      \
> +        tcg_out_st32_12(s, COND_AL, arg, TCG_REG_CALL_STACK, ofs);         \
> +    }                                                                      \
> +    return argreg + 1;                                                     \
> +}
> +
> +DEFINE_TCG_OUT_ARG(tcg_out_arg_imm32, uint32_t, tcg_out_movi32,
> +    (tcg_out_movi32(s, COND_AL, TCG_REG_R8, arg), arg = TCG_REG_R8))
> +DEFINE_TCG_OUT_ARG(tcg_out_arg_reg8, TCGReg, tcg_out_ext8u,
> +    (tcg_out_ext8u(s, COND_AL, TCG_REG_R8, arg), arg = TCG_REG_R8))
> +DEFINE_TCG_OUT_ARG(tcg_out_arg_reg16, TCGReg, tcg_out_ext16u,
> +    (tcg_out_ext16u(s, COND_AL, TCG_REG_R8, arg), arg = TCG_REG_R8))
> +DEFINE_TCG_OUT_ARG(tcg_out_arg_reg32, TCGReg, tcg_out_mov_reg, )
> +
> +static TCGReg tcg_out_arg_reg64(TCGContext *s, TCGReg argreg,
> +                                TCGReg arglo, TCGReg arghi)
>  {
>      /* 64 bit arguments must go in even/odd register pairs
>       * and in 8-aligned stack slots.
> @@ -1086,16 +1057,7 @@ static inline TCGReg tcg_out_arg_reg64(TCGContext *s, 
> TCGReg argreg,
>      argreg = tcg_out_arg_reg32(s, argreg, arghi);
>      return argreg;
>  }
> -
> -static inline void tcg_out_arg_stacktidy(TCGContext *s, TCGReg argreg)
> -{
> -    /* Output any necessary post-call cleanup of the stack */
> -    if (argreg > 4) {
> -        tcg_out_dat_imm(s, COND_AL, ARITH_ADD, TCG_REG_R13, TCG_REG_R13, 
> 0x10);
> -    }
> -}
> -
> -#endif
> +#endif /* SOFTMMU */
>  
>  #define TLB_SHIFT    (CPU_TLB_ENTRY_BITS + CPU_TLB_BITS)
>  
> @@ -1226,7 +1188,6 @@ static inline void tcg_out_qemu_ld(TCGContext *s, const 
> TCGArg *args, int opc)
>  #endif
>      argreg = tcg_out_arg_imm32(s, argreg, mem_index);
>      tcg_out_call(s, (tcg_target_long) qemu_ld_helpers[s_bits]);
> -    tcg_out_arg_stacktidy(s, argreg);
>  
>      switch (opc) {
>      case 0 | 4:
> @@ -1444,7 +1405,6 @@ static inline void tcg_out_qemu_st(TCGContext *s, const 
> TCGArg *args, int opc)
>  
>      argreg = tcg_out_arg_imm32(s, argreg, mem_index);
>      tcg_out_call(s, (tcg_target_long) qemu_st_helpers[s_bits]);
> -    tcg_out_arg_stacktidy(s, argreg);
>  
>      reloc_pc24(label_ptr, (tcg_target_long)s->code_ptr);
>  #else /* !CONFIG_SOFTMMU */
> @@ -1884,8 +1844,6 @@ static void tcg_target_init(TCGContext *s)
>      tcg_regset_set_reg(s->reserved_regs, TCG_REG_PC);
>  
>      tcg_add_target_add_op_defs(arm_op_defs);
> -    tcg_set_frame(s, TCG_AREG0, offsetof(CPUArchState, temp_buf),
> -                  CPU_TEMP_BUF_NLONGS * sizeof(long));
>  }
>  
>  static inline void tcg_out_ld(TCGContext *s, TCGType type, TCGReg arg,
> @@ -1914,18 +1872,32 @@ static inline void tcg_out_movi(TCGContext *s, 
> TCGType type,
>  
>  static void tcg_target_qemu_prologue(TCGContext *s)
>  {
> -    /* Calling convention requires us to save r4-r11 and lr;
> -     * save also r12 to maintain stack 8-alignment.
> -     */
> +    int frame_size;
> +
> +    /* Calling convention requires us to save r4-r11 and lr.  */
> +    /* stmdb sp!, { r4 - r11, lr } */
> +    tcg_out32(s, (COND_AL << 28) | 0x092d4ff0);
>  
> -    /* stmdb sp!, { r4 - r12, lr } */
> -    tcg_out32(s, (COND_AL << 28) | 0x092d5ff0);
> +    /* Allocate the local stack frame.  */
> +    frame_size = TCG_STATIC_CALL_ARGS_SIZE;
> +    frame_size += CPU_TEMP_BUF_NLONGS * sizeof(long);
> +    /* We saved an odd number of registers above; keep an 8 aligned stack.  
> */
> +    frame_size += 4;
> +

The above hardcoded value implies that TCG_STATIC_CALL_ARGS_SIZE and
CPU_TEMP_BUF_NLONGS are even numbers, which is currently true. Wouldn't
it be better to fix the alignement using the value of
TCG_TARGET_STACK_ALIGN like on other architectures?

> +    tcg_out_dat_rI(s, COND_AL, ARITH_SUB, TCG_REG_CALL_STACK,
> +                   TCG_REG_CALL_STACK, frame_size, 1);
> +    tcg_set_frame(s, TCG_REG_CALL_STACK, TCG_STATIC_CALL_ARGS_SIZE,
> +                  CPU_TEMP_BUF_NLONGS * sizeof(long));
>  
>      tcg_out_mov(s, TCG_TYPE_PTR, TCG_AREG0, tcg_target_call_iarg_regs[0]);
>  
>      tcg_out_bx(s, COND_AL, tcg_target_call_iarg_regs[1]);
>      tb_ret_addr = s->code_ptr;
>  
> -    /* ldmia sp!, { r4 - r12, pc } */
> -    tcg_out32(s, (COND_AL << 28) | 0x08bd9ff0);
> +    /* Epilogue.  We branch here via tb_ret_addr.  */
> +    tcg_out_dat_rI(s, COND_AL, ARITH_ADD, TCG_REG_CALL_STACK,
> +                   TCG_REG_CALL_STACK, frame_size, 1);
> +
> +    /* ldmia sp!, { r4 - r11, pc } */
> +    tcg_out32(s, (COND_AL << 28) | 0x08bd8ff0);
>  }

Otherwise looks fine.

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