osdep: Fix ROUND_UP(64-bit, 32-bit)
commit2098b073f398cd628c09c5a78537a6854e85830d
authorEric Blake <eblake@redhat.com>
Thu, 14 Sep 2017 13:49:23 +0000 (14 08:49 -0500)
committerMichael Tokarev <mjt@tls.msk.ru>
Tue, 26 Sep 2017 06:11:22 +0000 (26 09:11 +0300)
tree8dd62d1f997390298a4b708f006db6d294e4b0b4
parent2c5b1d2a479273cec4c1be491745f48b0808b508
osdep: Fix ROUND_UP(64-bit, 32-bit)

When using bit-wise operations that exploit the power-of-two
nature of the second argument of ROUND_UP(), we still need to
ensure that the mask is as wide as the first argument (done
by using a ternary to force proper arithmetic promotion).
Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512U) produces 0,
instead of the intended 2TiB, because negation of an unsigned
32-bit quantity followed by widening to 64-bits does not
sign-extend the mask.

Broken since its introduction in commit 292c8e50 (v1.5.0).
Callers that passed the same width type to both macro parameters,
or that had other code to ensure the first parameter's maximum
runtime value did not exceed the second parameter's width, are
unaffected, but I did not audit to see which (if any) existing
clients of the macro could trigger incorrect behavior (I found
the bug while adding a new use of the macro).

While preparing the patch, checkpatch complained about poor
spacing, so I also fixed that here and in the nearby DIV_ROUND_UP.

CC: qemu-trivial@nongnu.org
CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
include/qemu/osdep.h