If I have code like this:
char foo(char *p)
{
return (p[-1]);
}
It generates a negative index, like this:
* Function foo code
L 2,=F'-1'
L 3,0(11)
SLR 15,15
IC 15,0(2,3)
* Function foo epilogue
See that (2,3) - that is adding both R2 + R3.
R3 is a pointer to a location in 4 GiB space.
R2 is now 0xFFFFFFFF
In 64-bit mode, both of those values are added
together and there is no address wrap, so it
accesses memory above the 4 GiB boundary
(between 4 GiB and 8 GiB to be precise)
which I don't have access to.
Is there a way of constraining index registers to positive
values?
I want it to instead generate
ALR 3,2
to add these two values together using 32-bit arithmetic,
causing truncation at 32 bits, then it can do
IC 15,0(3)
(ie no index)
I'm using GCC 3.2.3 using the i370 target if it makes a difference.
Thanks. Paul.
