While the target is volatile, the temporary variables used to access the
target cast away the volatile. This is undefined behaviour, and a
compiler may optimise away/reorder these accesses, breaking the test.
This was observed with GCC 13.1.1, but it can be difficult to reproduce
because of the dependency on compiler behaviour.
Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230725005841.28854-5-bgray@linux.ibm.com
static void write_var(int len)
{
static void write_var(int len)
{
- __u8 *pcvar;
- __u16 *psvar;
- __u32 *pivar;
- __u64 *plvar;
+ volatile __u8 *pcvar;
+ volatile __u16 *psvar;
+ volatile __u32 *pivar;
+ volatile __u64 *plvar;
- pcvar = (__u8 *)&glvar;
+ pcvar = (volatile __u8 *)&glvar;
*pcvar = 0xff;
break;
case 2:
*pcvar = 0xff;
break;
case 2:
- psvar = (__u16 *)&glvar;
+ psvar = (volatile __u16 *)&glvar;
*psvar = 0xffff;
break;
case 4:
*psvar = 0xffff;
break;
case 4:
- pivar = (__u32 *)&glvar;
+ pivar = (volatile __u32 *)&glvar;
*pivar = 0xffffffff;
break;
case 8:
*pivar = 0xffffffff;
break;
case 8:
- plvar = (__u64 *)&glvar;
+ plvar = (volatile __u64 *)&glvar;
*plvar = 0xffffffffffffffffLL;
break;
}
*plvar = 0xffffffffffffffffLL;
break;
}
+ cvar = (volatile __u8)glvar;
+ svar = (volatile __u16)glvar;
+ ivar = (volatile __u32)glvar;
+ lvar = (volatile __u64)glvar;