Re: [Qemu-devel] [PATCH] target-i386:slightly refactor dr7 related function

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-12-03 04:07, liguang wrote:
> 1. define names of breakpoints in dr7
> 2. slightly refactor bits field of breakpoint
>    related functions.

Two topics, (at least) two patches, please. The code is hairy - not your
fault, you actually try to improve it. But splitting up makes review
easier. Thanks in advance.

> 
> Signed-off-by: liguang <lig.fnst@cn.fujitsu.com>
> ---
>  target-i386/cpu.h         |    6 ++++
>  target-i386/helper.c      |   59 ++++++++++++++++++++++++++++----------------
>  target-i386/machine.c     |    2 +-
>  target-i386/misc_helper.c |    4 +-
>  target-i386/seg_helper.c  |    4 +-
>  5 files changed, 48 insertions(+), 27 deletions(-)
> 
> diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> index 90ef1ff..2da6ea0 100644
> --- a/target-i386/cpu.h
> +++ b/target-i386/cpu.h
> @@ -231,6 +231,12 @@
>  #define DR7_TYPE_SHIFT  16
>  #define DR7_LEN_SHIFT   18
>  #define DR7_FIXED_1     0x00000400
> +#define DR7_L0_3        0x55

DR7_LOCAL_BP_MASK or so.

> +#define DR7_MAX_BP      4
> +#define DR7_BP_INST     0x0
> +#define DR7_DATA_WR     0x1
> +#define DR7_IO_RW       0x2
> +#define DR7_DATA_RW     0x3
>  
>  #define PG_PRESENT_BIT	0
>  #define PG_RW_BIT	1
> diff --git a/target-i386/helper.c b/target-i386/helper.c
> index bf206cf..54d6712 100644
> --- a/target-i386/helper.c
> +++ b/target-i386/helper.c
> @@ -966,27 +966,26 @@ hwaddr cpu_get_phys_page_debug(CPUX86State *env, target_ulong addr)
>  
>  void hw_breakpoint_insert(CPUX86State *env, int index)
>  {
> -    int type, err = 0;
> +    int type = 0, err = 0;
>  
>      switch (hw_breakpoint_type(env->dr[7], index)) {
> -    case 0:
> +    case DR7_BP_INST:
>          if (hw_breakpoint_enabled(env->dr[7], index))
>              err = cpu_breakpoint_insert(env, env->dr[index], BP_CPU,
>                                          &env->cpu_breakpoint[index]);
>          break;
> -    case 1:
> +    case DR7_DATA_WR:
>          type = BP_CPU | BP_MEM_WRITE;
> -        goto insert_wp;
> -    case 2:
> -         /* No support for I/O watchpoints yet */
> -        break;
> -    case 3:
> -        type = BP_CPU | BP_MEM_ACCESS;
> -    insert_wp:
> +    case DR7_DATA_RW:
> +        if (!type)
> +            type = BP_CPU | BP_MEM_ACCESS;

Coding style.

But, to be honest, I find the goto approach cleaner. Alternatively, test
for "type" (or "wp_type") != 0 outside the switch, moving the
cpu_watchpoint_insert there.

>          err = cpu_watchpoint_insert(env, env->dr[index],
>                                      hw_breakpoint_len(env->dr[7], index),
>                                      type, &env->cpu_watchpoint[index]);
>          break;
> +    case DR7_IO_RW:
> +         /* No support for I/O watchpoints yet */
> +        break;
>      }
>      if (err)
>          env->cpu_breakpoint[index] = NULL;
> @@ -997,15 +996,15 @@ void hw_breakpoint_remove(CPUX86State *env, int index)
>      if (!env->cpu_breakpoint[index])
>          return;
>      switch (hw_breakpoint_type(env->dr[7], index)) {
> -    case 0:
> +    case DR7_BP_INST:
>          if (hw_breakpoint_enabled(env->dr[7], index))
>              cpu_breakpoint_remove_by_ref(env, env->cpu_breakpoint[index]);
>          break;
> -    case 1:
> -    case 3:
> +    case DR7_DATA_WR:
> +    case DR7_DATA_RW:
>          cpu_watchpoint_remove_by_ref(env, env->cpu_watchpoint[index]);
>          break;
> -    case 2:
> +    case DR7_IO_RW:
>          /* No support for I/O watchpoints yet */
>          break;
>      }
> @@ -1014,22 +1013,38 @@ void hw_breakpoint_remove(CPUX86State *env, int index)
>  int check_hw_breakpoints(CPUX86State *env, int force_dr6_update)
>  {
>      target_ulong dr6;
> -    int reg, type;
> +    int index, type = 0;
>      int hit_enabled = 0;
>  
>      dr6 = env->dr[6] & ~0xf;
> -    for (reg = 0; reg < 4; reg++) {
> -        type = hw_breakpoint_type(env->dr[7], reg);
> -        if ((type == 0 && env->dr[reg] == env->eip) ||
> -            ((type & 1) && env->cpu_watchpoint[reg] &&
> -             (env->cpu_watchpoint[reg]->flags & BP_WATCHPOINT_HIT))) {
> -            dr6 |= 1 << reg;
> -            if (hw_breakpoint_enabled(env->dr[7], reg))
> +    for (index = 0; index < DR7_MAX_BP; index++) {
> +        switch (hw_breakpoint_type(env->dr[7], index)) {
> +        case DR7_BP_INST:
> +            if (env->dr[index] != env->eip)
> +                break;
> +            type = 1;

"type" is not very telling as it is used here. Either continue to assign
it to hw_breakpoint_type and clear it on DR7_IO_RW, or rename it to a
boolean like "bp_match".

> +            break;
> +        case DR7_DATA_WR:
> +        case DR7_DATA_RW:
> +            if (!env->cpu_watchpoint[index])
> +                break;
> +            if (!(env->cpu_watchpoint[index]->flags & BP_WATCHPOINT_HIT))
> +                break;

Let's fold these two into one.

In general: coding style.

> +            type = 1;
> +            break;
> +        case DR7_IO_RW:
> +            break;
> +        }
> +        if (type) {
> +            dr6 |= 1 << index;
> +            if (hw_breakpoint_enabled(env->dr[7], index))
>                  hit_enabled = 1;
> +            type = 0;

If you go for "wp_match", just set to false under DR7_IO_RW.

>          }
>      }
>      if (hit_enabled || force_dr6_update)
>          env->dr[6] = dr6;
> +
>      return hit_enabled;
>  }
>  
> diff --git a/target-i386/machine.c b/target-i386/machine.c
> index 4771508..a4b1a1e 100644
> --- a/target-i386/machine.c
> +++ b/target-i386/machine.c
> @@ -265,7 +265,7 @@ static int cpu_post_load(void *opaque, int version_id)
>  
>      cpu_breakpoint_remove_all(env, BP_CPU);
>      cpu_watchpoint_remove_all(env, BP_CPU);
> -    for (i = 0; i < 4; i++)
> +    for (i = 0; i < DR7_MAX_BP; i++)

If touching the line, please fix the coding style as well.

>          hw_breakpoint_insert(env, i);
>  
>      tlb_flush(env, 1);
> diff --git a/target-i386/misc_helper.c b/target-i386/misc_helper.c
> index a020379..5ee0863 100644
> --- a/target-i386/misc_helper.c
> +++ b/target-i386/misc_helper.c
> @@ -197,11 +197,11 @@ void helper_movl_drN_T0(CPUX86State *env, int reg, target_ulong t0)
>          env->dr[reg] = t0;
>          hw_breakpoint_insert(env, reg);
>      } else if (reg == 7) {
> -        for (i = 0; i < 4; i++) {
> +        for (i = 0; i < DR7_MAX_BP; i++) {
>              hw_breakpoint_remove(env, i);
>          }
>          env->dr[7] = t0;
> -        for (i = 0; i < 4; i++) {
> +        for (i = 0; i < DR7_MAX_BP; i++) {
>              hw_breakpoint_insert(env, i);
>          }
>      } else {
> diff --git a/target-i386/seg_helper.c b/target-i386/seg_helper.c
> index ff93374..317187b 100644
> --- a/target-i386/seg_helper.c
> +++ b/target-i386/seg_helper.c
> @@ -465,8 +465,8 @@ static void switch_tss(CPUX86State *env, int tss_selector,
>  
>  #ifndef CONFIG_USER_ONLY
>      /* reset local breakpoints */
> -    if (env->dr[7] & 0x55) {
> -        for (i = 0; i < 4; i++) {
> +    if (env->dr[7] & DR7_L0_3) {
> +        for (i = 0; i < DR7_MAX_BP; i++) {
>              if (hw_breakpoint_enabled(env->dr[7], i) == 0x1) {

There is a magic value remaining here. You probably want defines for the
local vs. global enable bits as well.

>                  hw_breakpoint_remove(env, i);
>              }
> 

Jan

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