Re: [PATCH] spi: lp-8841: return correct error code from probe

[Sergei Ianovich <ynvich@xxxxxxxxx>]

Hi Arnd,

On Thu, 2016-02-25 at 12:37 +0100, Arnd Bergmann wrote:
> The spi_lp8841_rtc_probe() function misses an initialization of the
> return code when it fails to get its memory resource, as gcc notices:
> 
> drivers/spi/spi-lp8841-rtc.c: In function 'spi_lp8841_rtc_probe':
> drivers/spi/spi-lp8841-rtc.c:239:9: error: 'ret' may be used
> uninitialized in this function [-Werror=maybe-uninitialized]

I wasn't getting this warning when I was building the driver. This
happened because -Wmaybe-uninitialized is suppressed when
CONFIG_CC_OPTIMIZE_FOR_SIZE is selected
(Commit e74fc973b6e531fef1fce8b101ffff05ecfb774c "Turn off -Wmaybe-
uninitialized when building with -Os").

A recent gcc version like 5.3.1 doesn't seem to produce much false
positives. May it make sense to revert that commit?

The gcc-5.3.1 log for reference.

---8<---
$ arm-linux-gnueabi-gcc --version
arm-linux-gnueabi-gcc (Debian 5.3.1-8) 5.3.1 20160205
$ make -j 4 -s KCFLAGS=-Wmaybe-uninitialized
ipc/shm.c: In function 'SyS_shmdt':
ipc/shm.c:1344:59: warning: 'file' may be used uninitialized in this function [-Wmaybe-uninitialized]
       ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
                                                           ^
ipc/shm.c:1267:15: note: 'file' was declared here
  struct file *file;
               ^
mm/vmscan.c: In function 'shrink_zone':
mm/vmscan.c:2418:18: warning: 'lru_pages' may be used uninitialized in this function [-Wmaybe-uninitialized]
    unsigned long lru_pages;
                  ^
drivers/gpio/gpiolib-of.c: In function 'of_gpiochip_add':
drivers/gpio/gpiolib-of.c:221:7: warning: 'dflags' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if (gpiod_hog(desc, name, lflags, dflags))
       ^
drivers/gpio/gpiolib-of.c:211:19: note: 'dflags' was declared here
  enum gpiod_flags dflags;
                   ^
drivers/gpio/gpiolib-of.c:221:7: warning: 'lflags' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if (gpiod_hog(desc, name, lflags, dflags))
       ^
drivers/gpio/gpiolib-of.c:210:25: note: 'lflags' was declared here
  enum gpio_lookup_flags lflags;
                         ^
net/core/dev.c: In function 'validate_xmit_skb_list':
net/core/dev.c:2984:15: warning: 'tail' may be used uninitialized in this function [-Wmaybe-uninitialized]
    tail->next = skb;
               ^
drivers/spi/spi-lp8841-rtc.c: In function 'spi_lp8841_rtc_probe':
drivers/spi/spi-lp8841-rtc.c:239:9: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ret;
         ^
net/sunrpc/svcauth_unix.c: In function 'unix_gid_parse':
net/sunrpc/svcauth_unix.c:510:2: warning: 'gids' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for (i = 0 ; i < gids ; i++) {
  ^
In file included from include/linux/sunrpc/svcauth.h:16:0,
                 from include/linux/sunrpc/svc.h:18,
                 from include/linux/sunrpc/svcsock.h:12,
                 from net/sunrpc/svcauth_unix.c:6:
include/linux/sunrpc/cache.h:306:9: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv - boot.tv_sec;
         ^
include/linux/sunrpc/cache.h:298:9: note: 'rv' was declared here
  time_t rv;
         ^
net/sunrpc/svcauth_unix.c: In function 'ip_map_parse':
include/linux/sunrpc/cache.h:306:9: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv - boot.tv_sec;
         ^
include/linux/sunrpc/cache.h:298:9: note: 'rv' was declared here
  time_t rv;
         ^
In file included from net/sunrpc/cache.c:34:0:
net/sunrpc/cache.c: In function 'write_flush':
include/linux/sunrpc/cache.h:306:9: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv - boot.tv_sec;
         ^
include/linux/sunrpc/cache.h:298:9: note: 'rv' was declared here
  time_t rv;
         ^
net/sunrpc/auth_gss/svcauth_gss.c: In function 'rsc_parse':
net/sunrpc/auth_gss/svcauth_gss.c:456:22: warning: 'id' may be used uninitialized in this function [-Wmaybe-uninitialized]
   rsci.cred.cr_uid = make_kuid(&init_user_ns, id);
                      ^
In file included from include/linux/sunrpc/svcauth.h:16:0,
                 from include/linux/sunrpc/svc.h:18,
                 from include/linux/sunrpc/auth_gss.h:17,
                 from net/sunrpc/auth_gss/svcauth_gss.c:46:
include/linux/sunrpc/cache.h:306:9: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv - boot.tv_sec;
         ^
include/linux/sunrpc/cache.h:298:9: note: 'rv' was declared here
  time_t rv;
         ^
net/sunrpc/auth_gss/svcauth_gss.c: In function 'rsi_parse':
include/linux/sunrpc/cache.h:306:9: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv - boot.tv_sec;
         ^
include/linux/sunrpc/cache.h:298:9: note: 'rv' was declared here
  time_t rv;
         ^
---8<---
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