win32-arm-low.c regptr 96 bits stored in 32 bit variable

win32-arm-low.c regptr 96 bits stored in 32 bit variable

[Bill Morgan]

Should this static variable ULONG zero be at least 96 bits?

static char *
regptr (CONTEXT* c, int r)
{
  if (mappings[r] < 0)
  {
    static ULONG zero;
    /* Always force value to zero, in case the user tried to write
       to this register before.  */
    zero = 0;
    return (char *) &zero;
  }
  else
    return (char *) c + mappings[r];
}

reg-arm.dat shows 96 bits for the ones that have mappings[r] == -1

name:arm
xmlarch:arm
expedite:r11,sp,pc
32:r0
32:r1
32:r2
32:r3
32:r4
32:r5
32:r6
32:r7
32:r8
32:r9
32:r10
32:r11
32:r12
32:sp
32:lr
32:pc
96:f0
96:f1
96:f2
96:f3
96:f4
96:f5
96:f6
96:f7
32:fps
32:cpsr

Re: win32-arm-low.c regptr 96 bits stored in 32 bit variable

[Simon Marchi]

On 2018-10-26 18:40, Bill Morgan wrote:
> Should this static variable ULONG zero be at least 96 bits?
> 
> static char *
> regptr (CONTEXT* c, int r)
> {
>   if (mappings[r] < 0)
>   {
>     static ULONG zero;
>     /* Always force value to zero, in case the user tried to write
>        to this register before.  */
>     zero = 0;
>     return (char *) &zero;
>   }
>   else
>     return (char *) c + mappings[r];
> }
> 
> reg-arm.dat shows 96 bits for the ones that have mappings[r] == -1
> 
> name:arm
> xmlarch:arm
> expedite:r11,sp,pc
> 32:r0
> 32:r1
> 32:r2
> 32:r3
> 32:r4
> 32:r5
> 32:r6
> 32:r7
> 32:r8
> 32:r9
> 32:r10
> 32:r11
> 32:r12
> 32:sp
> 32:lr
> 32:pc
> 96:f0
> 96:f1
> 96:f2
> 96:f3
> 96:f4
> 96:f5
> 96:f6
> 96:f7
> 32:fps
> 32:cpsr

Hi Bill,

By inspection, it does seem like a mistake, and that we would need to 
return a pointer to a buffer at least as big as register r.  But I have 
no idea how to build/run/test gdbserver on win32/arm.  If you are able 
to confirm that there is a problem and test a fix, could you please 
provide a patch?

To avoid this kind of problem again, we could return a pointer to a 
dynamically-sized buffer adjusted to the size of the register.  
Something like this:

static char *
regptr (CONTEXT* c, struct regcache *regcache, int r)
{
   if (mappings[r] < 0)
   {
     static gdb::byte_vector zero;
     /* Always force value to zero, in case the user tried to write
        to this register before.  */
     zero.assign (regcache_register_size (regcache, r), 0);
     return (char *) zero.data ();
   }
   else
     return (char *) c + mappings[r];
}

Simon

Re: win32-arm-low.c regptr 96 bits stored in 32 bit variable

[Richard Earnshaw (lists)]

Surely nobody is interested in the long-dead FPA architecture these
days.  I'm not sure why GDB still supports it.

R.

On 28/10/2018 16:47, Simon Marchi wrote:
> On 2018-10-26 18:40, Bill Morgan wrote:
>> Should this static variable ULONG zero be at least 96 bits?
>>
>> static char *
>> regptr (CONTEXT* c, int r)
>> {
>>   if (mappings[r] < 0)
>>   {
>>     static ULONG zero;
>>     /* Always force value to zero, in case the user tried to write
>>        to this register before.  */
>>     zero = 0;
>>     return (char *) &zero;
>>   }
>>   else
>>     return (char *) c + mappings[r];
>> }
>>
>> reg-arm.dat shows 96 bits for the ones that have mappings[r] == -1
>>
>> name:arm
>> xmlarch:arm
>> expedite:r11,sp,pc
>> 32:r0
>> 32:r1
>> 32:r2
>> 32:r3
>> 32:r4
>> 32:r5
>> 32:r6
>> 32:r7
>> 32:r8
>> 32:r9
>> 32:r10
>> 32:r11
>> 32:r12
>> 32:sp
>> 32:lr
>> 32:pc
>> 96:f0
>> 96:f1
>> 96:f2
>> 96:f3
>> 96:f4
>> 96:f5
>> 96:f6
>> 96:f7
>> 32:fps
>> 32:cpsr
> 
> Hi Bill,
> 
> By inspection, it does seem like a mistake, and that we would need to
> return a pointer to a buffer at least as big as register r.  But I have
> no idea how to build/run/test gdbserver on win32/arm.  If you are able
> to confirm that there is a problem and test a fix, could you please
> provide a patch?
> 
> To avoid this kind of problem again, we could return a pointer to a
> dynamically-sized buffer adjusted to the size of the register. 
> Something like this:
> 
> static char *
> regptr (CONTEXT* c, struct regcache *regcache, int r)
> {
>   if (mappings[r] < 0)
>   {
>     static gdb::byte_vector zero;
>     /* Always force value to zero, in case the user tried to write
>        to this register before.  */
>     zero.assign (regcache_register_size (regcache, r), 0);
>     return (char *) zero.data ();
>   }
>   else
>     return (char *) c + mappings[r];
> }
> 
> Simon

Re: win32-arm-low.c regptr 96 bits stored in 32 bit variable

[Simon Marchi]

On 2018-10-29 09:50, Richard Earnshaw (lists) wrote:
> Surely nobody is interested in the long-dead FPA architecture these
> days.  I'm not sure why GDB still supports it.

If it's really useless to support it today and it's just dead weight, it 
would be ideal if somebody from ARM (that has the full picture of the 
situation) made a patch to remove it.

Thanks,

Simon