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linux_tcp/poll: fix undefined behavior in select 

The select(2) system call on Linux now includes the restrict qualifier
on the fd_set pointers passed in, causing a diagnostic in gcc9 for the
call blocking for both read and write.  Pass a pointer to a temporary
copy of the set when two references are required.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
This commit is contained in:
Peter A. Bigot 2019-05-30 10:19:52 -05:00
parent 19d82ed1f2
commit a6930f5c36
1 changed files with 5 additions and 3 deletions
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8
src/linux_tcp/poll.h
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@ -106,8 +106,11 @@ public:
*/
bool active(bool block)
{
// accommodate restrict qualifier on fd_set params
fd_set set2 = _set;
// wait for the socket
if (block) return select(_socket + 1, &_set, &_set, nullptr, nullptr) > 0;
if (block) return select(_socket + 1, &_set, &set2, nullptr, nullptr) > 0;
// we do not want to block, so we use a small timeout
struct timeval timeout;
@ -116,7 +119,7 @@ public:
timeout.tv_sec = timeout.tv_usec = 0;
// no timeout at all
return select(_socket + 1, &_set, &_set, nullptr, &timeout) > 0;
return select(_socket + 1, &_set, &set2, nullptr, &timeout) > 0;
}
};
@ -124,4 +127,3 @@ public:
* End of namespace
*/
}