head -r356640 and mixed signed/unsigned comparisons

[Mark Millard]

The code:

394	                for (j = 0; j < addr_cells - 1; j++) {

looks wrong to me. Evidence follows.

/usr/src/sys/dev/ofw/openfirm.h:typedef uint32_t        pcell_t;
/usr/include/sys/_stdint.h:typedef      __uint32_t              uint32_t;
/usr/include/machine/_types.h:typedef   unsigned int            __uint32_t;

So pcell_t and int are of the same rank but different
unsigned vs. signed status.

From sys/powerpc/mpc85xx/lbc.c :

363	static int
364	fdt_lbc_reg_decode(phandle_t node, struct lbc_softc *sc,
365	    struct lbc_devinfo *di)
366	{
. . .
369	        pcell_t addr_cells, size_cells;
. . .
371	        int i, j, rv, bank;
. . .
394	                for (j = 0; j < addr_cells - 1; j++) {
395	                        start <<= 32;
396	                        start |= reg[j];
397	                }

So, for line 394, after the usual arithmetic
conversions for the "-" and then for the "<"
the line would look like (consolidating
some relevant material to be more
textually-local for ease of comparison):

for (int j = 0; (unsigned int)j < addr_cells-1u; j++)

For addr_cells==0u: addr_cells-1u == UINT_MAX .

So, for addr_cells==0u substituted (at run-time):

for (int j = 0; (unsigned int)j < UINT_MAX; j++)

So, unless it is guaranteed that 0u<addr_cells,
there would appear to be a looping problem here.

It appears to me that the condition:

addr_cells==0u && 0u<size_cells

would fail the tuples <= 0 test and so continue
on to try to use line 394.

But I do not have context to know the
condition would be a worrisome issue.


===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)