cppcheck: add/correct reason for cppcheck-suppress

Adding and correcting description/rational on why certain cppcheck
warnings or errors are intentionally suppressed.

core/clist.c

@@ -134,7 +134,8 @@ clist_node_t *_clist_sort(clist_node_t *list, clist_cmp_func_t cmp)
             p = q;
         }
 
-        /* cppcheck-suppress nullPointer */
+        /* cppcheck-suppress nullPointer
+         * (reason: tail cannot be NULL at this point, because list != NULL) */
         tail->next = list;
 
         /* If we have done only one merge, we're finished. */

cpu/cortexm_common/vectors_cortexm.c

@@ -237,7 +237,7 @@ __attribute__((used)) void hard_fault_handler(uint32_t* sp, uint32_t corrupted,
      * Fixes wrong compiler warning by gcc < 6.0. */
     uint32_t pc = 0;
     /* cppcheck-suppress variableScope
-     * variable used in assembly-code below */
+     * (reason: used within __asm__ which cppcheck doesn't pick up) */
     uint32_t* orig_sp = NULL;
 
     /* Check if the ISR stack overflowed previously. Not possible to detect

cpu/fe310/periph/uart.c

@@ -80,7 +80,8 @@ int uart_init(uart_t dev, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
     /* Calculate buadrate divisor given current CPU clk rate
      * Ignore the first run (icache needs to be warm) */
     uartDiv = PRCI_measure_mcycle_freq(1000, RTC_FREQ);
-    /* cppcheck-suppress redundantAssignment */
+    /* cppcheck-suppress redundantAssignment
+     * (reason: should ignore first cycle to get correct values) */
     uartDiv = PRCI_measure_mcycle_freq(1000, RTC_FREQ);
     uartDiv = uartDiv / baudrate;
 

cpu/kinetis/periph/i2c.c

@@ -170,7 +170,7 @@ static uint8_t i2c_find_divider(unsigned freq, unsigned speed)
 static inline void i2c_clear_irq_flags(I2C_Type *i2c)
 {
     /* cppcheck-suppress selfAssignment
-     * reason: intentional self assignment to clear all pending IRQs */
+     * (reason: intentional self assignment to clear all pending IRQs) */
     i2c->S = i2c->S;
 }
 

cpu/kinetis/periph/timer.c

@@ -436,7 +436,7 @@ static inline int lptmr_set(uint8_t dev, uint16_t timeout)
         hw->CNR = 0;
         hw->CMR = timeout + hw->CNR;
         /* cppcheck-suppress selfAssignment
-         * Clear IRQ flags */
+         * (reason: intentional self assignment to clear all pending IRQs) */
         hw->CSR = hw->CSR;
         /* Enable timer and IRQ */
         hw->CSR = LPTMR_CSR_TEN_MASK | LPTMR_CSR_TFC_MASK | LPTMR_CSR_TIE_MASK;
@@ -469,7 +469,7 @@ static inline int lptmr_set_absolute(uint8_t dev, uint16_t target)
         /* TCF is set, safe to update CMR live */
         hw->CMR = target - lptmr[dev].cnr;
         /* cppcheck-suppress selfAssignment
-         * Clear IRQ flags */
+         * (reason: intentional self assignment to clear all pending IRQs) */
         hw->CSR = hw->CSR;
         /* Enable timer and IRQ */
         hw->CSR = LPTMR_CSR_TEN_MASK | LPTMR_CSR_TFC_MASK | LPTMR_CSR_TIE_MASK;

cpu/mips32r2_common/newlib_syscalls_mips_uhi/syscalls.c

@@ -69,11 +69,8 @@ void _exit(int n)
 {
     exit(n);
 
-    /*
+    /* cppcheck-suppress unreachableCode
-     * Disable unreachableCode cppcheck as pm_off spins indefinately after
+     * (reason: pm_off spins indefinately after pulling the plug) */
-     * pulling the plug
-     */
-    /* cppcheck-suppress unreachableCode */
     pm_off();
 }
 

dist/tools/tunslip/tunslip6.c

@@ -191,7 +191,7 @@ serial_to_tun(FILE *inslip, int outfd)
     } uip;
     static unsigned int inbufptr = 0;
     /* cppcheck-suppress variableScope
-     * rationale: cannot be reduced if built on linux */
+     * (reason: cannot be reduced if built on linux) */
     int ret;
     unsigned char c;
 

drivers/adt7310/adt7310.c

@@ -218,8 +218,8 @@ float adt7310_read_float(const adt7310_t *dev)
 {
     int16_t raw = adt7310_read_raw(dev);
     if (raw == INT16_MIN) {
-        /* ignore cppcheck: we want to create a NaN here */
+        /* cppcheck-suppress duplicateExpression
-        /* cppcheck-suppress duplicateExpression */
+         * (reason: we want to create a NaN here) */
         return (0.0f / 0.0f); /* return NaN */
     }
     if (!dev->high_res) {

sys/net/gnrc/transport_layer/tcp/gnrc_tcp_eventloop.c

@@ -55,7 +55,8 @@ static int _send(gnrc_pktsnip_t *pkt)
 
     /* Search for TCP header */
     LL_SEARCH_SCALAR(pkt, tcp, type, GNRC_NETTYPE_TCP);
-    /* cppcheck-suppress knownConditionTrueFalse */
+    /* cppcheck-suppress knownConditionTrueFalse
+     * (reason: tcp *can* be != NULL after LL_SEARCH_SCALAR) */
     if (tcp == NULL) {
         DEBUG("gnrc_tcp_eventloop : _send() : tcp header missing.\n");
         gnrc_pktbuf_release(pkt);

sys/net/gnrc/transport_layer/tcp/gnrc_tcp_fsm.c

@@ -482,7 +482,8 @@ static int _fsm_rcvd_pkt(gnrc_tcp_tcb_t *tcb, gnrc_pktsnip_t *in_pkt)
                 if (ipv6_addr_is_link_local((ipv6_addr_t *) tcb->peer_addr)) {
                     gnrc_pktsnip_t *tmp = NULL;
                     LL_SEARCH_SCALAR(in_pkt, tmp, type, GNRC_NETTYPE_NETIF);
-                    /* cppcheck-suppress knownConditionTrueFalse */
+                    /* cppcheck-suppress knownConditionTrueFalse
+                     * (reason: tmp *can* be != NULL after LL_SEARCH_SCALAR) */
                     if (tmp == NULL) {
                         DEBUG("gnrc_tcp_fsm.c : _fsm_rcvd_pkt() :\
                                incomming packet had no netif header\n");

sys/quad_math/qdivrem.c

@@ -79,7 +79,7 @@ __qdivrem(u_quad_t uq, u_quad_t vq, u_quad_t *arq)
         static volatile const unsigned int zero = 0;
 
         /* cppcheck-suppress zerodiv
-         * Divission by zero is on purpose here */
+         * (reason: division by zero is on purpose here) */
         tmp.ul[H] = tmp.ul[L] = 1 / zero;
 
         if (arq) {

sys/universal_address/universal_address.c

@@ -98,7 +98,8 @@ static universal_address_container_t *universal_address_get_next_unused_entry(vo
      * (reason: UNIVERSAL_ADDRESS_MAX_ENTRIES may be zero in which case this
      * code is optimized out) */
     if (universal_address_table_filled < UNIVERSAL_ADDRESS_MAX_ENTRIES) {
-        /* cppcheck-suppress unsignedLessThanZero */
+        /* cppcheck-suppress unsignedLessThanZero
+         * (reason: UNIVERSAL_ADDRESS_MAX_ENTRIES may be zero, see above) */
         for (size_t i = 0; i < UNIVERSAL_ADDRESS_MAX_ENTRIES; ++i) {
             if (universal_address_table[i].use_count == 0) {
                 return &(universal_address_table[i]);

tests/buttons/main.c

@@ -69,7 +69,7 @@ int main(void)
 
     puts("On-board button test\n");
     /* cppcheck-suppress knownConditionTrueFalse
-     * rationale: board-dependent ifdefs */
+     * (reason: board-dependent ifdefs) */
     if (cnt == 0) {
         puts("[FAILED] no buttons available!");
         return 2;

tests/cpp11_condition_variable/main.cpp

@@ -53,7 +53,7 @@ int main() {
     {
       lock_guard<mutex> lk(m);
       /* cppcheck-suppress unreadVariable
-       * (reason variable is read in the thread created above) */
+       * (reason: variable is read in the thread created above) */
       ready = true;
       cv.notify_one();
     }

tests/leds/main.c

@@ -78,7 +78,7 @@ int main(void)
 
     puts("On-board LED test\n");
     /* cppcheck-suppress knownConditionTrueFalse
-     * rationale: board-dependent ifdefs */
+     * (reason: board-dependent ifdefs) */
     if (numof == 0) {
         puts("NO LEDs AVAILABLE");
     }