[PATCH 0/2] gdbstub: Unbreak i386 with gdb remote

[PATCH 0/2] gdbstub: Unbreak i386 with gdb remote

[Peter Xu]

It's silently broken on master during an refactoring.  Let's fix it.

Please feel free to drop patch 1 if it's not rc material, but I guess
we want patch 2...

Thanks,

Peter Xu (2):
  gdbstub: Assert len read from each register
  gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

 gdbstub.c             | 11 ++++++++---
 target/i386/gdbstub.c |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

-- 
2.24.1

[PATCH 1/2] gdbstub: Assert len read from each register

[Peter Xu]

This can expose the issue earlier on which register returned the wrong
result.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 gdbstub.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index 171e150950..f763545e81 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -911,17 +911,22 @@ static int gdb_read_register(CPUState *cpu, GByteArray *buf, int reg)
     CPUClass *cc = CPU_GET_CLASS(cpu);
     CPUArchState *env = cpu->env_ptr;
     GDBRegisterState *r;
+    int len = 0, orig_len = buf->len;
 
     if (reg < cc->gdb_num_core_regs) {
-        return cc->gdb_read_register(cpu, buf, reg);
+        len = cc->gdb_read_register(cpu, buf, reg);
     }
 
     for (r = cpu->gdb_regs; r; r = r->next) {
         if (r->base_reg <= reg && reg < r->base_reg + r->num_regs) {
-            return r->get_reg(env, buf, reg - r->base_reg);
+            len = r->get_reg(env, buf, reg - r->base_reg);
+            break;
         }
     }
-    return 0;
+
+    assert(len == buf->len - orig_len);
+
+    return len;
 }
 
 static int gdb_write_register(CPUState *cpu, uint8_t *mem_buf, int reg)
-- 
2.24.1

Re: [PATCH 1/2] gdbstub: Assert len read from each register

[Philippe Mathieu-Daudé]

On 4/9/20 6:49 PM, Peter Xu wrote:
> This can expose the issue earlier on which register returned the wrong
> result.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   gdbstub.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index 171e150950..f763545e81 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -911,17 +911,22 @@ static int gdb_read_register(CPUState *cpu, GByteArray *buf, int reg)
>       CPUClass *cc = CPU_GET_CLASS(cpu);
>       CPUArchState *env = cpu->env_ptr;
>       GDBRegisterState *r;
> +    int len = 0, orig_len = buf->len;
>   
>       if (reg < cc->gdb_num_core_regs) {
> -        return cc->gdb_read_register(cpu, buf, reg);
> +        len = cc->gdb_read_register(cpu, buf, reg);

This change the code flow. We could add ...:

            goto out;

>       }

... or use else?
>   
>       for (r = cpu->gdb_regs; r; r = r->next) {
>           if (r->base_reg <= reg && reg < r->base_reg + r->num_regs) {
> -            return r->get_reg(env, buf, reg - r->base_reg);
> +            len = r->get_reg(env, buf, reg - r->base_reg);
> +            break;
>           }
>       }
> -    return 0;
> +

   out:

> +    assert(len == buf->len - orig_len);
> +
> +    return len;
>   }
>   
>   static int gdb_write_register(CPUState *cpu, uint8_t *mem_buf, int reg)
> 

Re: [PATCH 1/2] gdbstub: Assert len read from each register

[Peter Xu]

On Thu, Apr 09, 2020 at 07:51:49PM +0200, Philippe Mathieu-Daudé wrote:
> On 4/9/20 6:49 PM, Peter Xu wrote:
> > This can expose the issue earlier on which register returned the wrong
> > result.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >   gdbstub.c | 11 ++++++++---
> >   1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/gdbstub.c b/gdbstub.c
> > index 171e150950..f763545e81 100644
> > --- a/gdbstub.c
> > +++ b/gdbstub.c
> > @@ -911,17 +911,22 @@ static int gdb_read_register(CPUState *cpu, GByteArray *buf, int reg)
> >       CPUClass *cc = CPU_GET_CLASS(cpu);
> >       CPUArchState *env = cpu->env_ptr;
> >       GDBRegisterState *r;
> > +    int len = 0, orig_len = buf->len;
> >       if (reg < cc->gdb_num_core_regs) {
> > -        return cc->gdb_read_register(cpu, buf, reg);
> > +        len = cc->gdb_read_register(cpu, buf, reg);
> 
> This change the code flow. We could add ...:

I didn't expect the "if" and "for" would collapse each other, but yeah
that could still be better.

Thanks,

> 
>            goto out;
> 
> >       }
> 
> ... or use else?
> >       for (r = cpu->gdb_regs; r; r = r->next) {
> >           if (r->base_reg <= reg && reg < r->base_reg + r->num_regs) {
> > -            return r->get_reg(env, buf, reg - r->base_reg);
> > +            len = r->get_reg(env, buf, reg - r->base_reg);
> > +            break;
> >           }
> >       }
> > -    return 0;
> > +
> 
>   out:
> 
> > +    assert(len == buf->len - orig_len);
> > +
> > +    return len;
> >   }
> >   static int gdb_write_register(CPUState *cpu, uint8_t *mem_buf, int reg)
> > 
> 

-- 
Peter Xu

[PATCH 2/2] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

[Peter Xu]

We should only pass in gdb_get_reg16() with the GByteArray* object
itself, no need to shift.  Without this patch, gdb remote attach will
crash QEMU.

Cc: Alex Bennée <alex.bennee@linaro.org>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 target/i386/gdbstub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
index f3d23b614e..b98a99500a 100644
--- a/target/i386/gdbstub.c
+++ b/target/i386/gdbstub.c
@@ -106,7 +106,7 @@ int x86_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
     } else if (n >= IDX_FP_REGS && n < IDX_FP_REGS + 8) {
         floatx80 *fp = (floatx80 *) &env->fpregs[n - IDX_FP_REGS];
         int len = gdb_get_reg64(mem_buf, cpu_to_le64(fp->low));
-        len += gdb_get_reg16(mem_buf + len, cpu_to_le16(fp->high));
+        len += gdb_get_reg16(mem_buf, cpu_to_le16(fp->high));
         return len;
     } else if (n >= IDX_XMM_REGS && n < IDX_XMM_REGS + CPU_NB_REGS) {
         n -= IDX_XMM_REGS;
-- 
2.24.1

Re: [PATCH 2/2] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

[Philippe Mathieu-Daudé]

On 4/9/20 6:49 PM, Peter Xu wrote:
> We should only pass in gdb_get_reg16() with the GByteArray* object
> itself, no need to shift.  Without this patch, gdb remote attach will
> crash QEMU.

You are correct.

Fixes: a010bdbe719 ("extend GByteArray to read register helpers")

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Same problem in m68k_fpu_gdb_get_reg().

TODO for 5.1, rename mem_buf -> array.

> 
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   target/i386/gdbstub.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
> index f3d23b614e..b98a99500a 100644
> --- a/target/i386/gdbstub.c
> +++ b/target/i386/gdbstub.c
> @@ -106,7 +106,7 @@ int x86_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
>       } else if (n >= IDX_FP_REGS && n < IDX_FP_REGS + 8) {
>           floatx80 *fp = (floatx80 *) &env->fpregs[n - IDX_FP_REGS];
>           int len = gdb_get_reg64(mem_buf, cpu_to_le64(fp->low));
> -        len += gdb_get_reg16(mem_buf + len, cpu_to_le16(fp->high));
> +        len += gdb_get_reg16(mem_buf, cpu_to_le16(fp->high));
>           return len;
>       } else if (n >= IDX_XMM_REGS && n < IDX_XMM_REGS + CPU_NB_REGS) {
>           n -= IDX_XMM_REGS;
> 

Re: [PATCH 2/2] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

[Peter Xu]

Hi, Phil,

On Thu, Apr 09, 2020 at 07:21:04PM +0200, Philippe Mathieu-Daudé wrote:
> On 4/9/20 6:49 PM, Peter Xu wrote:
> > We should only pass in gdb_get_reg16() with the GByteArray* object
> > itself, no need to shift.  Without this patch, gdb remote attach will
> > crash QEMU.
> 
> You are correct.
> 
> Fixes: a010bdbe719 ("extend GByteArray to read register helpers")

Oh I forgot to paste the fix line.  However, is it b7b8756a9c
("target/i386: use gdb_get_reg helpers", 2020-03-17) instead?

> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Thanks!

> 
> Same problem in m68k_fpu_gdb_get_reg().
> 
> TODO for 5.1, rename mem_buf -> array.

-- 
Peter Xu

Re: [PATCH 2/2] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

[Philippe Mathieu-Daudé]

On 4/9/20 8:01 PM, Peter Xu wrote:
> Hi, Phil,
> 
> On Thu, Apr 09, 2020 at 07:21:04PM +0200, Philippe Mathieu-Daudé wrote:
>> On 4/9/20 6:49 PM, Peter Xu wrote:
>>> We should only pass in gdb_get_reg16() with the GByteArray* object
>>> itself, no need to shift.  Without this patch, gdb remote attach will
>>> crash QEMU.
>>
>> You are correct.
>>
>> Fixes: a010bdbe719 ("extend GByteArray to read register helpers")
> 
> Oh I forgot to paste the fix line.  However, is it b7b8756a9c
> ("target/i386: use gdb_get_reg helpers", 2020-03-17) instead?

b7b8756a9c is correct, at that time the codebase was using the correct 
API. the next commit updated the API but missed to update the lines you 
are fixed. So I think "fixes a010bdbe719" is correct.

> 
>>
>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> 
> Thanks!
> 
>>
>> Same problem in m68k_fpu_gdb_get_reg().
>>
>> TODO for 5.1, rename mem_buf -> array.
> 

Re: [PATCH 2/2] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

[Alex Bennée]

Peter Xu <peterx@redhat.com> writes:

> We should only pass in gdb_get_reg16() with the GByteArray* object
> itself, no need to shift.  Without this patch, gdb remote attach will
> crash QEMU.
>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Queued to for-5.0/more-random-fixes, thanks.

> ---
>  target/i386/gdbstub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
> index f3d23b614e..b98a99500a 100644
> --- a/target/i386/gdbstub.c
> +++ b/target/i386/gdbstub.c
> @@ -106,7 +106,7 @@ int x86_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
>      } else if (n >= IDX_FP_REGS && n < IDX_FP_REGS + 8) {
>          floatx80 *fp = (floatx80 *) &env->fpregs[n - IDX_FP_REGS];
>          int len = gdb_get_reg64(mem_buf, cpu_to_le64(fp->low));
> -        len += gdb_get_reg16(mem_buf + len, cpu_to_le16(fp->high));
> +        len += gdb_get_reg16(mem_buf, cpu_to_le16(fp->high));
>          return len;
>      } else if (n >= IDX_XMM_REGS && n < IDX_XMM_REGS + CPU_NB_REGS) {
>          n -= IDX_XMM_REGS;


-- 
Alex Bennée