Re: [arm-gnu] bug or me doing something wrong?

[Gene Smith <gds@xxxxxxxxxxxxx>]

Gene Smith wrote:
> I have a function that accepts a uint16_t parameter. And I have a global 
> variable of type int16_t. They are both set to zero. But inside the 
> function I compare them, if (a==b), and they compare not equal. In the 
> assembly language the compare is actually "cmp r0, r2" where r0 is 
> 0xc000000 and r2 0x0 so they compare not equal.
>
> Note: r2 is the global var and gets setup with ldrh r2, [r3, #4] and it 
> looks correct.  while r0 is the function parameter and gets set from r6 
> at beginning of function and r6 contain 0xc000000. (Don't immediately 
> see where r6 is set.)
>
> Also, should I see a warning about comparing signed to unsigned with 
> -Wall -Wextra --pedantic ?
>
> This is with opt level -0s.
>
> -gene

--- bad	2010-02-12 13:51:12.000000000 -0500
+++ good	2010-02-12 13:57:40.000000000 -0500
@@ -26,10 +26,11 @@
  8000128:       0c40            lsrs    r0, r0, #17
         }

-        if (rcvd_seq == exp_seq)
+        if ((uint16_t)rcvd_seq == exp_seq)
  800012a:       4b1b            ldr     r3, [pc, #108]  (8000198 
<program_segment+0x84>)
  800012c:       889a            ldrh    r2, [r3, #4]
- 800012e:       4290            cmp     r0, r2
- 8000130:       d127            bne.n   8000182 <program_segment+0x6e>
+ 800012e:       b283            uxth    r3, r0
+ 8000130:       4293            cmp     r3, r2
+ 8000132:       d127            bne.n   8000184 <program_segment+0x70>
         {

If I don't cast rcvd_seq (the function param) it fails to see rcvd_seq 
and exp_seq as equal when they are both zero. Also, no warning that this 
might be a problem with -Wall -Wextra and -pedantic.