From c089583e504df752f98008319a6a48aee16b2059 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Mon, 17 Jul 2017 10:13:34 -0500 Subject: [PATCH] usb: Fix build with newer gcc MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit gcc 7 is pickier about our sources: hw/usb/bus.c: In function ‘usb_port_location’: hw/usb/bus.c:410:66: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size between 0 and 15 [-Werror=format-truncation=] snprintf(downstream->path, sizeof(downstream->path), "%s.%d", ^~ hw/usb/bus.c:410:9: note: ‘snprintf’ output between 3 and 28 bytes into a destination of size 16 snprintf(downstream->path, sizeof(downstream->path), "%s.%d", ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ upstream->path, portnr); ~~~~~~~~~~~~~~~~~~~~~~~ But we know that there are at most 5 levels of USB hubs, with at most two digits per level; that plus the separating dots means we use at most 15 bytes (including trailing NUL) of our 16-byte field. Adding an assertion to show gcc that we checked for truncation is enough to shut up the false-positive warning. Inspired by an idea by Dr. David Alan Gilbert . Signed-off-by: Eric Blake Reviewed-by: Philippe Mathieu-Daudé Message-id: 20170717151334.17954-1-eblake@redhat.com Signed-off-by: Gerd Hoffmann (cherry picked from commit 121829cb2160e9cd82482c1542699fa589688106) --- hw/usb/bus.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/hw/usb/bus.c b/hw/usb/bus.c index 25913ad488..9c4e5cbcf8 100644 --- a/hw/usb/bus.c +++ b/hw/usb/bus.c @@ -406,8 +406,10 @@ void usb_register_companion(const char *masterbus, USBPort *ports[], void usb_port_location(USBPort *downstream, USBPort *upstream, int portnr) { if (upstream) { - snprintf(downstream->path, sizeof(downstream->path), "%s.%d", - upstream->path, portnr); + int l = snprintf(downstream->path, sizeof(downstream->path), "%s.%d", + upstream->path, portnr); + /* Max string is nn.nn.nn.nn.nn, which fits in 16 bytes */ + assert(l < sizeof(downstream->path)); downstream->hubcount = upstream->hubcount + 1; } else { snprintf(downstream->path, sizeof(downstream->path), "%d", portnr); -- 2.39.5