Re: volatile is not volatile enough

[Richard Earnshaw <rearnsha at arm dot com>]

> Hi,
> 
> given a statement like
>   int a[2];
>   func2(func1(a), a[0], a[1]);
> where a is modified by func1, func2 receives wrong input on the stack. In
> detail, first a[1], then a[0] and then a is pushed onto the stack, then func1
> gets called and pops off its a -- which is modified after.
> Adding the keyword volatile doesnot help.
> 
> I am using gcc 3.3 20030226 (prerelease) SuSE Linux 8.2.
> 
> Here is a test script:
> #include <stdio.h>
> #define volatile
> 
> volatile void *func1(volatile int[]);
> volatile void *func2(volatile void *, volatile int, volatile int);
> 
> int main(void) {
>   volatile int a[2] = {13, 101};
>   volatile void *result;
> 
>   /* IMPACT
>      The result on stdout should be x=14 y=102 not x=13 y=101.
>   */
>   func2(func1(a), a[0], a[1]);
> 

Wrong.  The result is unspecified.  iso/iec 9899:1990 6.3.2.2 "The order 
of evaluation of the function designator, the arguments and subexpressions 
within the arguments is unspecified, but there is a sequence point before 
the actual call."

R.