[ovs-dev] [PATCH] extract-ofp-errors: Avoid unintentional sign extension in generated code.

[Ben Pfaff]

Code generated by this program includes constructs like this:

    switch (((uint64_t) vendor << 32) | (type << 16) | code)

with variables uint32_t vendor, uint16_t type, uint16_t code.  By C rules,
"type << 16" has type "int", which means that it will be sign-extended to
64 bits when ORed with uint64_t.  Thus, if 'type' has bit 15 set, then
the overall result will have all of its top 32 bits set, which is not
the desired result.

This commit fixes the problem.

No actual error types used in OVS or OpenFlow have bit 15 set, so this
does not fix a user-visible problem.

Found by Coverity.

Reported-at: https://scan3.coverity.com/reports.htm#v16889/p10449/fileInstanceId=14762955&defectInstanceId=4304798&mergedDefectId=180406
Signed-off-by: Ben Pfaff <blp at ovn.org>
---
 build-aux/extract-ofp-errors | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/build-aux/extract-ofp-errors b/build-aux/extract-ofp-errors
index 9642593d2458..6fea550f90b7 100755
--- a/build-aux/extract-ofp-errors
+++ b/build-aux/extract-ofp-errors
@@ -391,7 +391,7 @@ static const char *error_comments[OFPERR_N_ERRORS] = {
 static enum ofperr
 %s_decode(uint32_t vendor, uint16_t type, uint16_t code)
 {
-    switch (((uint64_t) vendor << 32) | (type << 16) | code) {""" % name)
+    switch (((uint64_t) vendor << 32) | (uint32_t) (type << 16) | code) {""" % name)
         found = set()
         for enum in names:
             if enum not in map:
@@ -405,7 +405,7 @@ static enum ofperr
                 vendor_s = "(%#xULL << 32) | " % vendor
             else:
                 vendor_s = ""
-            print ("    case %s(%d << 16) | %d:" % (vendor_s, type_, code))
+            print ("    case %s(uint32_t) (%d << 16) | %d:" % (vendor_s, type_, code))
             print ("        return OFPERR_%s;" % enum)
         print ("""\
     }
-- 
2.10.2