[lwip-devel] [bug #19167] tcp timeout handler can cause crash being invoked by sys_sem_wait()

[Dmitry Potapov]

Follow-up Comment #4, bug #19167 (project lwip):

Using of timestamps instead of time-delta does NOT require 64-bit.

/* timestamp_t value in milliseconds taken by module 2^32,
   so after 0xFFFFFFFF should be 0. */
typedef u32_t timestamp_t;
typedef s32_t timediff_t;

Now we need to define TIMESTAMP_DIFF macro that calculates the difference
between two timestamp_t values taken into account overflow and return it as
timediff_t, and TIMESTAMP_ADD which adds some timeout value to the given
timestamp.

Practically all modern processors use two's complement to represent signed
integers. So you can define them as

#define TIMESTAMP_DIFF(t1, t2) ((timediff_t)((t1) - (t2)))
#define TIMESTAMP_ADD(timestamp, timeout) \
 ((timestamp_t)((timestamp)+(timeout)))

then you can write

timediff_t timeout = TIMESTAMP_DIFF(timeouts->next->expires,
sys_time_now());
if (timeout > 0)
        sys_arch_mbox_fetch(mbox, msg, timeout)
else
        timeout_handler();


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