[v1] gdbstub: Unbreak i386 with gdb remote

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

Posted by Peter Xu 5 years, 10 months ago

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

Posted by Philippe Mathieu-Daudé 5 years, 10 months ago

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

Posted by Peter Xu 5 years, 10 months ago

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

Posted by Philippe Mathieu-Daudé 5 years, 10 months ago

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

Posted by Alex Bennée 5 years, 10 months ago

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