Squashed commit of the following:

binfmt/, configs/, grahics/, libc/, mm/, net/, sched/:  OS references to the errno variable should always use the set_errno(), get_errno() macros
    arch/arm/src/stm32 and stm32f7:  Architecture-specific code is not permitted to modify the errno variable.  drivers/ and libc/:  OS references to the errno variable should always use the set_errno(), get_errno() macros

arch/arm/src/stm32/stm32_comp.c

@@ -1069,7 +1069,6 @@ FAR struct comp_dev_s* stm32_compinitialize(int intf)
   if (ret < 0)
     {
       aerr("ERROR: Failed to initialize COMP%d: %d\n", intf, ret);
-      errno = -ret;
       return NULL;
     }
 

arch/arm/src/stm32/stm32_hrtim.c

@@ -5313,7 +5313,6 @@ FAR struct hrtim_dev_s* stm32_hrtiminitialize(void)
       if (ret < 0)
         {
           tmrerr("ERROR: Failed to initialize HRTIM1: %d\n", ret);
-          errno = -ret;
           return NULL;
         }
 

arch/arm/src/stm32/stm32_opamp.c

@@ -1402,7 +1402,6 @@ FAR struct opamp_dev_s* stm32_opampinitialize(int intf)
   if (ret < 0)
     {
       aerr("ERROR: Failed to initialize OPAMP%d: %d\n", intf, ret);
-      errno = -ret;
       return NULL;
     }
 

arch/arm/src/stm32f7/stm32_dma2d.c

@@ -2261,7 +2261,6 @@ FAR struct dma2d_layer_s *stm32_dma2dinitltdc(FAR struct stm32_ltdc_s *layer)
     {
       lcderr("ERROR: Returning -EINVAL, unsupported pixel format: %d\n",
              layer->vinfo.fmt);
-      errno = -EINVAL;
       return NULL;
     }
 

binfmt/libelf/libelf_init.c

@@ -101,7 +101,7 @@ static inline int elf_filelen(FAR struct elf_loadinfo_s *loadinfo,
   ret = stat(filename, &buf);
   if (ret < 0)
     {
-      int errval = errno;
+      int errval = get_errno();
       berr("Failed to stat file: %d\n", errval);
       return -errval;
     }
@@ -165,7 +165,7 @@ int elf_init(FAR const char *filename, FAR struct elf_loadinfo_s *loadinfo)
   loadinfo->filfd = open(filename, O_RDONLY);
   if (loadinfo->filfd < 0)
     {
-      int errval = errno;
+      int errval = get_errno();
       berr("Failed to open ELF binary %s: %d\n", filename, errval);
       return -errval;
     }

binfmt/libelf/libelf_read.c

@@ -127,7 +127,7 @@ int elf_read(FAR struct elf_loadinfo_s *loadinfo, FAR uint8_t *buffer,
       rpos = lseek(loadinfo->filfd, offset, SEEK_SET);
       if (rpos != offset)
         {
-          int errval = errno;
+          int errval = get_errno();
           berr("Failed to seek to position %lu: %d\n",
                (unsigned long)offset, errval);
           return -errval;

binfmt/libnxflat/libnxflat_init.c

@@ -111,7 +111,7 @@ int nxflat_init(const char *filename, struct nxflat_loadinfo_s *loadinfo)
   loadinfo->filfd = open(filename, O_RDONLY);
   if (loadinfo->filfd < 0)
     {
-      int errval = errno;
+      int errval = get_errno();
       berr("Failed to open NXFLAT binary %s: %d\n", filename, errval);
       return -errval;
     }

binfmt/libnxflat/libnxflat_read.c

@@ -131,7 +131,7 @@ int nxflat_read(struct nxflat_loadinfo_s *loadinfo, char *buffer,
       rpos = lseek(loadinfo->filfd, offset, SEEK_SET);
       if (rpos != offset)
         {
-          int errval = errno;
+          int errval = get_errno();
           berr("Failed to seek to position %d: %d\n", offset, errval);
           return -errval;
         }

configs/sama5d4-ek/src/at25_main.c

@@ -144,7 +144,7 @@ int at25_main(int argc, char *argv)
   fd = open(g_at25dev, O_WRONLY);
   if (fd < 0)
     {
-      int errcode = errno;
+      int errcode = get_errno();
       fprintf(stderr, "ERROR: Failed to open %s: %d\n", g_at25dev, errcode);
       return EXIT_FAILURE;
     }
@@ -205,7 +205,7 @@ int at25_main(int argc, char *argv)
       nwritten = write(fd, src, memoutstream.public.nput);
       if (nwritten <= 0)
         {
-          int errcode = errno;
+          int errcode = get_errno();
           if (errno != EINTR)
             {
               fprintf(stderr, "ERROR: Write failed: %d\n", errcode);
@@ -235,7 +235,7 @@ int at25_main(int argc, char *argv)
   fd = open(g_at25dev, O_RDONLY);
   if (fd < 0)
     {
-      int errcode = errno;
+      int errcode = get_errno();
       fprintf(stderr, "ERROR: Failed to open %s: %d\n", g_at25dev, errcode);
       return EXIT_FAILURE;
     }
@@ -254,7 +254,7 @@ int at25_main(int argc, char *argv)
       nread = read(fd, g_iobuffer, rdsize);
       if (nread <= 0)
         {
-          int errcode = errno;
+          int errcode = get_errno();
           if (errno != EINTR)
             {
               fprintf(stderr, "ERROR: Read failed: %d\n", errcode);

drivers/net/telnet.c

@@ -863,7 +863,7 @@ static int telnet_session(FAR struct telnet_session_s *session)
                priv->td_minor);
 
       ret = stat(session->ts_devpath, &statbuf);
-      DEBUGASSERT(ret >= 0 || errno == ENOENT);
+      DEBUGASSERT(ret >= 0 || get_errno() == ENOENT);
     }
   while (ret >= 0 && start != g_telnet_common.tc_minor);
 

graphics/nxmu/nx_start.c

@@ -190,7 +190,7 @@ int nx_start(void)
                               CONFIG_NXSTART_SERVERSTACK, nx_server, NULL);
       if (server < 0)
         {
-          int errcode = errno;
+          int errcode = get_errno();
           DEBUGASSERT(errcode > 0);
 
           gerr("ERROR: Failed to create nx_server kernel thread: %d\n", errcode);

libc/modlib/modlib_init.c

@@ -98,7 +98,7 @@ static inline int modlib_filelen(FAR struct mod_loadinfo_s *loadinfo,
   ret = stat(filename, &buf);
   if (ret < 0)
     {
-      int errval = errno;
+      int errval = get_errno();
       serr("ERROR: Failed to stat file: %d\n", errval);
       return -errval;
     }
@@ -163,7 +163,7 @@ int modlib_initialize(FAR const char *filename,
   loadinfo->filfd = open(filename, O_RDONLY);
   if (loadinfo->filfd < 0)
     {
-      int errval = errno;
+      int errval = get_errno();
       serr("ERROR: Failed to open ELF binary %s: %d\n", filename, errval);
       return -errval;
     }

libc/modlib/modlib_read.c

@@ -121,7 +121,7 @@ int modlib_read(FAR struct mod_loadinfo_s *loadinfo, FAR uint8_t *buffer,
       rpos = lseek(loadinfo->filfd, offset, SEEK_SET);
       if (rpos != offset)
         {
-          int errval = errno;
+          int errval = get_errno();
           serr("ERROR: Failed to seek to position %lu: %d\n",
                (unsigned long)offset, errval);
           return -errval;

libc/netdb/lib_dnsaddserver.c

@@ -90,7 +90,7 @@ int dns_add_nameserver(FAR const struct sockaddr *addr, socklen_t addrlen)
   stream = fopen(CONFIG_NETDB_RESOLVCONF_PATH, "at");
   if (stream == NULL)
     {
-      int errcode = errno;
+      int errcode = get_errno();
       nerr("ERROR: Failed to open %s: %d\n",
            CONFIG_NETDB_RESOLVCONF_PATH, errcode);
       DEBUGASSERT(errcode > 0);

libc/netdb/lib_dnsforeach.c

@@ -104,7 +104,7 @@ int dns_foreach_nameserver(dns_callback_t callback, FAR void *arg)
   stream = fopen(CONFIG_NETDB_RESOLVCONF_PATH, "rb");
   if (stream == NULL)
     {
-      int errcode = errno;
+      int errcode = get_errno();
       nerr("ERROR: Failed to open %s: %d\n",
         CONFIG_NETDB_RESOLVCONF_PATH, errcode);
       DEBUGASSERT(errcode > 0);

libc/netdb/lib_gethostbyaddrr.c

@@ -263,7 +263,7 @@ int lib_hostfile_lookup(FAR const void *addr, socklen_t len, int type,
   stream = fopen(CONFIG_NETDB_HOSTCONF_PATH, "r");
   if (stream == NULL)
     {
-      int errcode = errno;
+      int errcode = get_errno();
 
       nerr("ERROR:  Failed to open the hosts file %s: %d\n",
            CONFIG_NETDB_HOSTCONF_PATH, errcode);

libc/netdb/lib_gethostbynamer.c

@@ -597,7 +597,7 @@ static int lib_hostfile_lookup(FAR const char *name, FAR struct hostent *host,
   stream = fopen(CONFIG_NETDB_HOSTCONF_PATH, "r");
   if (stream == NULL)
     {
-      int errcode = errno;
+      int errcode = get_errno();
 
       nerr("ERROR:  Failed to open the hosts file %s: %d\n",
            CONFIG_NETDB_HOSTCONF_PATH, errcode);

libc/pthread/pthread_setcancelstate.c

@@ -85,7 +85,7 @@ int pthread_setcancelstate(int state, FAR int *oldstate)
   ret = task_setcancelstate(state, oldstate);
   if (ret < 0)
     {
-      ret = errno;
+      ret = get_errno();
     }
 
   return ret;

libc/pthread/pthread_setcanceltype.c

@@ -85,7 +85,7 @@ int pthread_setcanceltype(int type, FAR int *oldtype)
   ret = task_setcanceltype(type, oldtype);
   if (ret < 0)
     {
-      ret = errno;
+      ret = get_errno();
     }
 
   return ret;

libc/stdio/lib_fclose.c

@@ -89,7 +89,7 @@ int fclose(FAR FILE *stream)
           if ((stream->fs_oflags & O_WROK) != 0)
             {
               ret = lib_fflush(stream, true);
-              errcode = errno;
+              errcode = get_errno();
             }
 
           /* Close the underlying file descriptor and save the return status */
@@ -103,7 +103,7 @@ int fclose(FAR FILE *stream)
           if (ret == OK)
             {
               ret = status;
-              errcode = errno;
+              errcode = get_errno();
             }
         }
 

libc/stdlib/lib_wctomb.c

@@ -66,7 +66,7 @@ int wctomb(FAR char *s, wchar_t wc)
 
   if ((size_t) wc >= 0x100)
     {
-      errno = EILSEQ;
+      set_errno(EILSEQ);
       return -1;
     }
 

libc/time/lib_localtime.c

@@ -2374,7 +2374,7 @@ static time_t time1(FAR struct tm *const tmp,
 
   if (tmp == NULL)
     {
-      errno = EINVAL;
+      set_errno(EINVAL);
       return -1;
     }
 

libc/wqueue/work_signal.c

@@ -98,7 +98,7 @@ int work_signal(int qid)
       ret = kill(g_usrwork.pid, SIGWORK);
       if (ret < 0)
         {
-          int errcode = errno;
+          int errcode = get_errno();
           ret = -errcode;
         }
     }

libc/wqueue/work_usrthread.c

@@ -360,7 +360,7 @@ int work_usrstart(void)
     DEBUGASSERT(g_usrwork.pid > 0);
     if (g_usrwork.pid < 0)
       {
-        int errcode = errno;
+        int errcode = get_errno();
         DEBUGASSERT(errcode > 0);
         return -errcode;
       }

mm/mm_heap/mm_sem.c

@@ -200,7 +200,7 @@ void mm_takesemaphore(FAR struct mm_heap_s *heap)
 #if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
               DEBUGASSERT(ret == -EINTR);
 #else
-              int errcode = errno;
+              int errcode = get_errno();
               DEBUGASSERT(errcode == EINTR);
               ret = -errcode;
 #endif

net/route/net_fileroute.c

@@ -170,7 +170,7 @@ int net_routesize(FAR const char *path, size_t entrysize)
        * created yet?
        */
 
-      errcode = errno;
+      errcode = get_errno();
       if (errcode == ENOENT)
         {
           /* The routing table file has not been created.  Return size zero. */

sched/wqueue/kwork_hpthread.c

@@ -162,7 +162,7 @@ int work_hpstart(void)
   DEBUGASSERT(pid > 0);
   if (pid < 0)
     {
-      int errcode = errno;
+      int errcode = get_errno();
       DEBUGASSERT(errcode > 0);
 
       serr("ERROR: kthread_create failed: %d\n", errcode);

sched/wqueue/kwork_lpthread.c

@@ -209,7 +209,7 @@ int work_lpstart(void)
       DEBUGASSERT(pid > 0);
       if (pid < 0)
         {
-          int errcode = errno;
+          int errcode = get_errno();
           DEBUGASSERT(errcode > 0);
 
           serr("ERROR: kthread_create %d failed: %d\n", wndx, errcode);