Date: Sat, 11 Jan 2020 17:28:22 -0800 From: Mark Millard <marklmi@yahoo.com> To: Justin Hibbits <chmeeedalf@gmail.com>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: head -r356640 and mixed signed/unsigned comparisons Message-ID: <18622739-BB2E-432B-B877-2FBE3A9D4ECB@yahoo.com> References: <18622739-BB2E-432B-B877-2FBE3A9D4ECB.ref@yahoo.com>
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The code:
394 for (j =3D 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.
=46rom 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 =3D 0; j < addr_cells - 1; j++) {
395 start <<=3D 32;
396 start |=3D 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 =3D 0; (unsigned int)j < addr_cells-1u; j++)
For addr_cells=3D=3D0u: addr_cells-1u =3D=3D UINT_MAX .
So, for addr_cells=3D=3D0u substituted (at run-time):
for (int j =3D 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=3D=3D0u && 0u<size_cells
would fail the tuples <=3D 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.
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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