2.6.14 assorted warnings

2.6.14 assorted warnings

[Keith Owens]

gcc 4.0.1 on i386, 2.6.14 assorted warnings.

arch/i386/kernel/cpu/transmeta.c: In function 'init_transmeta':
arch/i386/kernel/cpu/transmeta.c:11: warning: 'cpu_freq' may be used uninitialized in this function

kernel/kmod.c: In function '____call_usermodehelper':
kernel/kmod.c:138: warning: statement with no effect

fs/bio.c: In function 'bio_alloc_bioset':
fs/bio.c:167: warning: 'idx' may be used uninitialized in this function

fs/nfsd/nfsctl.c: In function 'write_filehandle':
fs/nfsd/nfsctl.c:262: warning: 'maxsize' may be used uninitialized in this function

fs/udf/balloc.c: In function 'udf_table_new_block':
fs/udf/balloc.c:757: warning: 'goal_eloc.logicalBlockNum' may be used uninitialized in this function

fs/udf/super.c: In function 'udf_load_partition':
fs/udf/super.c:1351: warning: 'ino.partitionReferenceNum' may be used uninitialized in this function

fs/xfs/xfs_alloc_btree.c: In function 'xfs_alloc_insrec':
fs/xfs/xfs_alloc_btree.c:622: warning: 'nrec.ar_startblock' may be used uninitialized in this function
fs/xfs/xfs_alloc_btree.c:622: warning: 'nrec.ar_blockcount' may be used uninitialized in this function

fs/xfs/xfs_bmap.c: In function 'xfs_bmap_alloc':
fs/xfs/xfs_bmap.c:2335: warning: 'rtx' is used uninitialized in this function

fs/xfs/xfs_dir2_sf.c: In function 'xfs_dir2_block_sfsize':
fs/xfs/xfs_dir2_sf.c:110: warning: 'parent' may be used uninitialized in this function

fs/xfs/xfs_dir_leaf.c: In function 'xfs_dir_leaf_to_shortform':
fs/xfs/xfs_dir_leaf.c:653: warning: 'parent' may be used uninitialized in this function

fs/xfs/xfs_ialloc_btree.c: In function 'xfs_inobt_insrec':
fs/xfs/xfs_ialloc_btree.c:750: warning: 'nrec.ir_free' is used uninitialized in this function
fs/xfs/xfs_ialloc_btree.c:750: warning: 'nrec.ir_freecount' is used uninitialized in this function
fs/xfs/xfs_ialloc_btree.c:567: warning: 'nrec.ir_startino' may be used uninitialized in this function

ipc/msg.c: In function 'sys_msgctl':
ipc/msg.c:333: warning: 'setbuf.qbytes' may be used uninitialized in this function
ipc/msg.c:333: warning: 'setbuf.uid' may be used uninitialized in this function
ipc/msg.c:333: warning: 'setbuf.gid' may be used uninitialized in this function
ipc/msg.c:333: warning: 'setbuf.mode' may be used uninitialized in this function

ipc/sem.c: In function 'semctl_down':
ipc/sem.c:803: warning: 'setbuf.uid' may be used uninitialized in this function
ipc/sem.c:803: warning: 'setbuf.gid' may be used uninitialized in this function
ipc/sem.c:803: warning: 'setbuf.mode' may be used uninitialized in this function

drivers/net/wireless/ipw2100.c: In function 'store_memory':
drivers/net/wireless/ipw2100.c:3756: warning: unused variable 'dev'
drivers/net/wireless/ipw2100.c: In function 'store_scan_age':
drivers/net/wireless/ipw2100.c:4065: warning: unused variable 'dev'

sound/core/oss/route.c: In function 'route_to_channel':
sound/core/oss/route.c:207: warning: 'src' may be used uninitialized in this function

lib/zlib_inflate/inftrees.c: In function 'huft_build':
lib/zlib_inflate/inftrees.c:121: warning: 'r.base' may be used uninitialized in this function

Stripped .config.

X86=y
SEMAPHORE_SLEEPERS=y
MMU=y
UID16=y
GENERIC_ISA_DMA=y
GENERIC_IOMAP=y
ARCH_MAY_HAVE_PC_FDC=y
EXPERIMENTAL=y
CLEAN_COMPILE=y
LOCK_KERNEL=y
INIT_ENV_ARG_LIMIT=32
LOCALVERSION="kaos"
SWAP=y
SYSVIPC=y
SYSCTL=y
HOTPLUG=y
KOBJECT_UEVENT=y
INITRAMFS_SOURCE=""
KALLSYMS=y
KALLSYMS_ALL=y
PRINTK=y
BUG=y
BASE_FULL=y
FUTEX=y
EPOLL=y
SHMEM=y
CC_ALIGN_FUNCTIONS=0
CC_ALIGN_LABELS=0
CC_ALIGN_LOOPS=0
CC_ALIGN_JUMPS=0
BASE_SMALL=0
MODULES=y
MODULE_UNLOAD=y
OBSOLETE_MODPARM=y
KMOD=y
STOP_MACHINE=y
X86_PC=y
M686=y
X86_CMPXCHG=y
X86_XADD=y
X86_L1_CACHE_SHIFT=5
RWSEM_XCHGADD_ALGORITHM=y
GENERIC_CALIBRATE_DELAY=y
X86_PPRO_FENCE=y
X86_WP_WORKS_OK=y
X86_INVLPG=y
X86_BSWAP=y
X86_POPAD_OK=y
X86_GOOD_APIC=y
X86_USE_PPRO_CHECKSUM=y
SMP=y
NR_CPUS=2
PREEMPT_NONE=y
PREEMPT_BKL=y
X86_LOCAL_APIC=y
X86_IO_APIC=y
X86_TSC=y
X86_MCE=y
X86_MSR=m
X86_CPUID=m
DCDBAS=m
NOHIGHMEM=y
SELECT_MEMORY_MODEL=y
FLATMEM_MANUAL=y
FLATMEM=y
FLAT_NODE_MEM_MAP=y
MTRR=y
IRQBALANCE=y
SECCOMP=y
HZ_250=y
HZ=250
PHYSICAL_START=0x100000
PM=y
ACPI=y
ACPI_AC=m
ACPI_BATTERY=m
ACPI_BUTTON=m
ACPI_VIDEO=m
ACPI_FAN=m
ACPI_PROCESSOR=m
ACPI_THERMAL=m
ACPI_ASUS=m
ACPI_IBM=m
ACPI_TOSHIBA=m
ACPI_BLACKLIST_YEAR=0
ACPI_EC=y
ACPI_POWER=y
ACPI_SYSTEM=y
X86_PM_TIMER=y
CPU_FREQ=y
CPU_FREQ_TABLE=y
CPU_FREQ_STAT=y
CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
CPU_FREQ_GOV_PERFORMANCE=y
CPU_FREQ_GOV_POWERSAVE=m
CPU_FREQ_GOV_USERSPACE=m
X86_ACPI_CPUFREQ=m
X86_SPEEDSTEP_ICH=m
X86_SPEEDSTEP_LIB=m
PCI=y
PCI_GOANY=y
PCI_BIOS=y
PCI_DIRECT=y
PCI_MMCONFIG=y
ISA_DMA_API=y
BINFMT_ELF=y
BINFMT_AOUT=m
BINFMT_MISC=m
NET=y
PACKET=m
UNIX=y
INET=y
IP_FIB_HASH=y
SYN_COOKIES=y
INET_DIAG=y
INET_TCP_DIAG=y
TCP_CONG_BIC=y
NETFILTER=y
IP_NF_CONNTRACK=m
IP_NF_FTP=m
IP_NF_IRC=m
IP_NF_QUEUE=m
IP_NF_IPTABLES=m
IP_NF_MATCH_LIMIT=m
IP_NF_MATCH_MAC=m
IP_NF_MATCH_PKTTYPE=m
IP_NF_MATCH_MARK=m
IP_NF_MATCH_MULTIPORT=m
IP_NF_MATCH_TOS=m
IP_NF_MATCH_ECN=m
IP_NF_MATCH_DSCP=m
IP_NF_MATCH_AH_ESP=m
IP_NF_MATCH_LENGTH=m
IP_NF_MATCH_TTL=m
IP_NF_MATCH_TCPMSS=m
IP_NF_MATCH_HELPER=m
IP_NF_MATCH_STATE=m
IP_NF_MATCH_CONNTRACK=m
IP_NF_MATCH_OWNER=m
IP_NF_FILTER=m
IP_NF_TARGET_REJECT=m
IP_NF_TARGET_LOG=m
IP_NF_TARGET_ULOG=m
IP_NF_TARGET_TCPMSS=m
IP_NF_NAT=m
IP_NF_NAT_NEEDED=y
IP_NF_TARGET_MASQUERADE=m
IP_NF_TARGET_REDIRECT=m
IP_NF_NAT_IRC=m
IP_NF_NAT_FTP=m
IP_NF_MANGLE=m
IP_NF_TARGET_TOS=m
IP_NF_TARGET_ECN=m
IP_NF_TARGET_DSCP=m
IP_NF_TARGET_MARK=m
IP_NF_ARPTABLES=m
IP_NF_ARPFILTER=m
VLAN_8021Q=m
IRDA=m
IRLAN=m
IRNET=m
IRCOMM=m
IRDA_ULTRA=y
IRDA_CACHE_LAST_LSAP=y
IRDA_FAST_RR=y
IRTTY_SIR=m
USB_IRDA=m
BT=m
BT_HCIUSB=m
BT_HCIUSB_SCO=y
BT_HCIUART=m
BT_HCIUART_H4=y
BT_HCIUART_BCSP=y
BT_HCIUART_BCSP_TXCRC=y
BT_HCIBCM203X=m
BT_HCIBFUSB=m
BT_HCIVHCI=m
IEEE80211=m
IEEE80211_CRYPT_WEP=m
IEEE80211_CRYPT_CCMP=m
IEEE80211_CRYPT_TKIP=m
STANDALONE=y
PREVENT_FIRMWARE_BUILD=y
FW_LOADER=m
CONNECTOR=m
PARPORT=m
PARPORT_PC=m
PARPORT_NOT_PC=y
BLK_DEV_FD=y
BLK_DEV_LOOP=m
BLK_DEV_RAM=y
BLK_DEV_RAM_COUNT=16
BLK_DEV_RAM_SIZE=4096
IOSCHED_NOOP=y
IOSCHED_AS=y
IOSCHED_DEADLINE=y
IOSCHED_CFQ=y
IDE=y
BLK_DEV_IDE=y
BLK_DEV_IDEDISK=y
BLK_DEV_IDECD=y
BLK_DEV_IDESCSI=y
IDE_GENERIC=y
BLK_DEV_IDEPCI=y
IDEPCI_SHARE_IRQ=y
BLK_DEV_IDEDMA_PCI=y
IDEDMA_PCI_AUTO=y
BLK_DEV_PIIX=y
BLK_DEV_IDEDMA=y
IDEDMA_AUTO=y
SCSI=y
SCSI_PROC_FS=y
BLK_DEV_SD=m
BLK_DEV_SR=m
BLK_DEV_SR_VENDOR=y
CHR_DEV_SG=m
SCSI_CONSTANTS=y
SCSI_LOGGING=y
SCSI_SPI_ATTRS=y
SCSI_SYM53C8XX_2=y
SCSI_SYM53C8XX_DMA_ADDRESSING_MODE=1
SCSI_SYM53C8XX_DEFAULT_TAGS=16
SCSI_SYM53C8XX_MAX_TAGS=64
SCSI_QLA2XXX=y
NETDEVICES=y
DUMMY=m
NET_ETHERNET=y
MII=m
NET_TULIP=y
TULIP=m
NET_PCI=y
E100=m
TIGON3=m
NET_RADIO=y
STRIP=m
IPW2100=m
IPW2100_MONITOR=y
IPW2200=m
AIRO=m
HERMES=m
PLX_HERMES=m
TMD_HERMES=m
NORTEL_HERMES=m
PCI_HERMES=m
ATMEL=m
PCI_ATMEL=m
PRISM54=m
HOSTAP=m
HOSTAP_FIRMWARE=y
HOSTAP_PLX=m
HOSTAP_PCI=m
NET_WIRELESS=y
PLIP=m
PPP=m
PPP_ASYNC=m
PPP_DEFLATE=m
PPP_BSDCOMP=m
SLIP=m
SLIP_COMPRESSED=y
INPUT=y
INPUT_MOUSEDEV=y
INPUT_MOUSEDEV_PSAUX=y
INPUT_MOUSEDEV_SCREEN_X=1024
INPUT_MOUSEDEV_SCREEN_Y=768
INPUT_KEYBOARD=y
KEYBOARD_ATKBD=y
INPUT_MOUSE=y
MOUSE_PS2=m
MOUSE_SERIAL=m
SERIO=y
SERIO_I8042=y
SERIO_SERPORT=y
SERIO_PCIPS2=m
SERIO_LIBPS2=y
VT=y
VT_CONSOLE=y
HW_CONSOLE=y
SERIAL_8250=y
SERIAL_8250_CONSOLE=y
SERIAL_8250_NR_UARTS=4
SERIAL_CORE=y
SERIAL_CORE_CONSOLE=y
UNIX98_PTYS=y
LEGACY_PTYS=y
LEGACY_PTY_COUNT=256
PRINTER=m
LP_CONSOLE=y
IPMI_HANDLER=m
IPMI_DEVICE_INTERFACE=m
IPMI_SI=m
IPMI_WATCHDOG=m
NVRAM=m
RTC=y
AGP=m
AGP_INTEL=m
DRM=m
DRM_RADEON=m
HPET=y
HPET_RTC_IRQ=y
HPET_MMAP=y
I2C=m
I2C_ALGOBIT=m
I2C_I801=m
I2C_I810=m
W1=m
W1_THERM=m
HWMON=m
VGA_CONSOLE=y
DUMMY_CONSOLE=y
SOUND=m
SND=m
SND_TIMER=m
SND_PCM=m
SND_HWDEP=m
SND_RAWMIDI=m
SND_SEQUENCER=m
SND_SEQ_DUMMY=m
SND_OSSEMUL=y
SND_MIXER_OSS=m
SND_PCM_OSS=m
SND_SEQUENCER_OSS=y
SND_RTCTIMER=m
SND_SEQ_RTCTIMER_DEFAULT=y
SND_GENERIC_DRIVER=y
SND_MPU401_UART=m
SND_DUMMY=m
SND_VIRMIDI=m
SND_MTPAV=m
SND_SERIAL_U16550=m
SND_MPU401=m
SND_AC97_CODEC=m
SND_AC97_BUS=m
SND_INTEL8X0=m
SND_USB_AUDIO=m
USB_ARCH_HAS_HCD=y
USB_ARCH_HAS_OHCI=y
USB=m
USB_DEVICEFS=y
USB_EHCI_HCD=m
USB_OHCI_HCD=m
USB_OHCI_LITTLE_ENDIAN=y
USB_UHCI_HCD=m
USB_ACM=m
USB_PRINTER=m
USB_STORAGE=m
USB_STORAGE_DATAFAB=y
USB_STORAGE_FREECOM=y
USB_STORAGE_ISD200=y
USB_STORAGE_DPCM=y
USB_STORAGE_SDDR09=y
USB_STORAGE_SDDR55=y
USB_STORAGE_JUMPSHOT=y
USB_HID=m
USB_HIDINPUT=y
HID_FF=y
USB_HIDDEV=y
USB_KBD=m
USB_MOUSE=m
USB_AIPTEK=m
USB_WACOM=m
USB_KBTAB=m
USB_POWERMATE=m
USB_MTOUCH=m
USB_EGALAX=m
USB_XPAD=m
USB_ATI_REMOTE=m
USB_MDC800=m
USB_MICROTEK=m
USB_DABUSB=m
USB_CATC=m
USB_KAWETH=m
USB_PEGASUS=m
USB_RTL8150=m
USB_USBNET=m
USB_NET_AX8817X=m
USB_NET_CDCETHER=m
USB_NET_NET1080=m
USB_NET_ZAURUS=m
USB_MON=y
USB_USS720=m
USB_SERIAL=m
USB_SERIAL_GENERIC=y
USB_SERIAL_BELKIN=m
USB_SERIAL_DIGI_ACCELEPORT=m
USB_SERIAL_EMPEG=m
USB_SERIAL_FTDI_SIO=m
USB_SERIAL_VISOR=m
USB_SERIAL_IPAQ=m
USB_SERIAL_IR=m
USB_SERIAL_EDGEPORT=m
USB_SERIAL_EDGEPORT_TI=m
USB_SERIAL_KEYSPAN_PDA=m
USB_SERIAL_KEYSPAN=m
USB_SERIAL_KEYSPAN_MPR=y
USB_SERIAL_KEYSPAN_USA28=y
USB_SERIAL_KEYSPAN_USA28X=y
USB_SERIAL_KEYSPAN_USA28XA=y
USB_SERIAL_KEYSPAN_USA28XB=y
USB_SERIAL_KEYSPAN_USA19=y
USB_SERIAL_KEYSPAN_USA18X=y
USB_SERIAL_KEYSPAN_USA19W=y
USB_SERIAL_KEYSPAN_USA19QW=y
USB_SERIAL_KEYSPAN_USA19QI=y
USB_SERIAL_KEYSPAN_USA49W=y
USB_SERIAL_KEYSPAN_USA49WLC=y
USB_SERIAL_KLSI=m
USB_SERIAL_KOBIL_SCT=m
USB_SERIAL_MCT_U232=m
USB_SERIAL_PL2303=m
USB_SERIAL_SAFE=m
USB_SERIAL_SAFE_PADDED=y
USB_SERIAL_CYBERJACK=m
USB_SERIAL_XIRCOM=m
USB_SERIAL_OMNINET=m
USB_EZUSB=y
USB_EMI62=m
USB_EMI26=m
USB_AUERSWALD=m
USB_RIO500=m
USB_LEGOTOWER=m
USB_LCD=m
USB_LED=m
USB_CYTHERM=m
USB_PHIDGETSERVO=m
USB_TEST=m
EXT2_FS=y
FS_POSIX_ACL=y
XFS_FS=y
XFS_EXPORT=y
XFS_QUOTA=y
MINIX_FS=m
ROMFS_FS=m
INOTIFY=y
QUOTACTL=y
DNOTIFY=y
AUTOFS_FS=m
AUTOFS4_FS=m
FUSE_FS=m
ISO9660_FS=m
JOLIET=y
ZISOFS=y
ZISOFS_FS=m
UDF_FS=m
UDF_NLS=y
FAT_FS=m
MSDOS_FS=m
VFAT_FS=m
FAT_DEFAULT_CODEPAGE=437
FAT_DEFAULT_IOCHARSET="iso8859-1"
NTFS_FS=m
PROC_FS=y
PROC_KCORE=y
SYSFS=y
TMPFS=y
RAMFS=y
RELAYFS_FS=m
EFS_FS=m
HPFS_FS=m
UFS_FS=m
NFS_FS=m
NFS_V3=y
NFS_V4=y
NFSD=m
NFSD_V3=y
NFSD_V4=y
NFSD_TCP=y
LOCKD=m
LOCKD_V4=y
EXPORTFS=y
NFS_COMMON=y
SUNRPC=m
SUNRPC_GSS=m
RPCSEC_GSS_KRB5=m
SMB_FS=m
MSDOS_PARTITION=y
NLS=y
NLS_DEFAULT="iso8859-1"
NLS_CODEPAGE_437=m
NLS_ISO8859_1=m
NLS_UTF8=m
DEBUG_KERNEL=y
MAGIC_SYSRQ=y
LOG_BUF_SHIFT=16
DETECT_SOFTLOCKUP=y
DEBUG_BUGVERBOSE=y
EARLY_PRINTK=y
X86_FIND_SMP_CONFIG=y
X86_MPPARSE=y
KDB=y
KDB_MODULES=y
KDB_CONTINUE_CATASTROPHIC=0
CRYPTO=y
CRYPTO_MD5=y
CRYPTO_DES=m
CRYPTO_AES=m
CRYPTO_ARC4=m
CRYPTO_MICHAEL_MIC=m
CRC_CCITT=m
CRC32=m
ZLIB_INFLATE=m
ZLIB_DEFLATE=m
GENERIC_HARDIRQS=y
GENERIC_IRQ_PROBE=y
GENERIC_PENDING_IRQ=y
X86_SMP=y
X86_HT=y
X86_BIOS_REBOOT=y
X86_TRAMPOLINE=y
PC=y

Re: 2.6.14 assorted warnings

[Jens Axboe]

On Fri, Oct 28 2005, Keith Owens wrote:
> fs/bio.c: In function 'bio_alloc_bioset':
> fs/bio.c:167: warning: 'idx' may be used uninitialized in this function

This is bogus. bio_alloc_bioset() passes in a pointer to a long which
bvec_alloc_bs() always fills, _unless_ it returns NULL. In the NULL case
we never use 'idx' (quite obvious, we bail immediately).

I didn't check the other warnings, but there may be similar cases in
other paths.

-- 
Jens Axboe

Re: 2.6.14 assorted warnings

[Dave Jones]

On Fri, Oct 28, 2005 at 05:21:19PM +1000, Keith Owens wrote:
 > gcc 4.0.1 on i386, 2.6.14 assorted warnings.
 > 
 > arch/i386/kernel/cpu/transmeta.c: In function 'init_transmeta':
 > arch/i386/kernel/cpu/transmeta.c:11: warning: 'cpu_freq' may be used uninitialized in this function
 > 
 > fs/bio.c: In function 'bio_alloc_bioset':
 > fs/bio.c:167: warning: 'idx' may be used uninitialized in this function

gcc is dumb, it doesn't realise that the variable will be filled by another
function if its passed thus..

	unsigned long foo
	bar(&foo)
	if (foo==1)
		...

With bar() filling in content of foo.
I believe there's at least once instance of this in gcc bugzilla.

		Dave

Re: 2.6.14 assorted warnings

[Arnd Bergmann]

On Freedag 28 Oktober 2005 09:30, Dave Jones wrote:
> gcc is dumb, it doesn't realise that the variable will be filled by another
> function if its passed thus..
> 
>         unsigned long foo
>         bar(&foo)
>         if (foo==1)
>                 ...
> 
> With bar() filling in content of foo.
> I believe there's at least once instance of this in gcc bugzilla.
> 
The case is more complicated here. gcc before 4.0 always assumed that
bar(&foo); initializes foo. gcc-4.0 now looks into bar if it is inlining
that and tries to find out if that really initializes foo in every
case.

In the example, bvec_alloc_bs does not initialize &idx when nr is not
between 1 and BIO_MAX_PAGES, so gcc is telling the truth here.

	Arnd <><

Re: 2.6.14 assorted warnings

[Richard Knutsson]

Dave Jones wrote:

>gcc is dumb, it doesn't realise that the variable will be filled by another
>function if its passed thus..
>
>	unsigned long foo
>	bar(&foo)
>	if (foo==1)
>		...
>
>With bar() filling in content of foo.
>I believe there's at least once instance of this in gcc bugzilla.
>  
>
Can we blame the compiler not knowing if the function bar will use the 
value of foo or initialize it?
For these cases, would it not be better to set them a value (for example 
0 or maybe UNINIT_DEFAULT)?
After all, the most common warning (as far as i can see) is about 
uninitialized variables.

Richard

Re: 2.6.14 assorted warnings

[Jens Axboe]

On Fri, Oct 28 2005, Arnd Bergmann wrote:
> In the example, bvec_alloc_bs does not initialize &idx when nr is not
> between 1 and BIO_MAX_PAGES, so gcc is telling the truth here.

Wrong. idx is always initialized if being used.

-- 
Jens Axboe

Re: 2.6.14 assorted warnings

[Richard Knutsson]

Jens Axboe wrote:

>On Fri, Oct 28 2005, Arnd Bergmann wrote:
>  
>
>>In the example, bvec_alloc_bs does not initialize &idx when nr is not
>>between 1 and BIO_MAX_PAGES, so gcc is telling the truth here.
>>    
>>
>
>Wrong. idx is always initialized if being used.
>
>  
>
Is the compiler really that smart as it searches back into the parent-function and try all the combinations? Otherwise, Arnd is correct.
And on an philosophical plane, can/should we put that responsibility onto the compiler? Is it not "easier" to make the functions take care
of its own duties (like the *nix-way) and make the bvec_alloc_bs initialize idx (even if it has to be an error-value)?

I'm thinking something like this. Seems alright?

/Richard

---

diff -Nurp a/fs/bio.c b/fs/bio.c
--- a/fs/bio.c	2005-10-29 06:30:49.000000000 +0200
+++ b/fs/bio.c	2005-10-29 06:33:00.000000000 +0200
@@ -90,6 +90,7 @@ static inline struct bio_vec *bvec_alloc
 		case  65 ... 128: *idx = 4; break;
 		case 129 ... BIO_MAX_PAGES: *idx = 5; break;
 		default:
+			*idx = -1;
 			return NULL;
 	}
 	/* 

Re: 2.6.14 assorted warnings

[Al Viro]

On Sat, Oct 29, 2005 at 07:59:54AM +0200, Richard Knutsson wrote:
> And on an philosophical plane, can/should we put that responsibility onto 
> the compiler? Is it not "easier" to make the functions take care
> of its own duties (like the *nix-way) and make the bvec_alloc_bs initialize 
> idx (even if it has to be an error-value)?
> 
> I'm thinking something like this. Seems alright?

No.  Working around the false positives in compiler warning system is
*wrong*.  _IF_ it cares to inline the function and generate the
warnings based on that, it is responsible for doing it right.

It's a gcc bug, plain and simple.

Re: 2.6.14 assorted warnings

[Alan Cox]

On Gwe, 2005-10-28 at 03:30 -0400, Dave Jones wrote:
> gcc is dumb, it doesn't realise that the variable will be filled by another
> function if its passed thus..
> 
> 	unsigned long foo
> 	bar(&foo)
> 	if (foo==1)
> 		...
> 
> With bar() filling in content of foo.
> I believe there's at least once instance of this in gcc bugzilla.

gcc is a *LOT* smarter than you give it credit for. It will not warn for
cases where it isn't able to tell how foo is used passed with &foo. It
will warn for cases where it can

Compile the following program with and without -O2 and you'll see just
how smart gcc actually is

#include <stdio.h>

static void bar(char *x) {
  *x = 1;
}

static void baz(char *x) {
  printf("Wombat\n");
}

int main(int argc, char *argv[]) {
  char x,y;
  bar(&x);
  baz(&y);

  printf("%c,%c\n", x, y);
}

So I'd go look deeper for real bugs 

Alan

Re: 2.6.14 assorted warnings

[Al Viro]

On Sun, Oct 30, 2005 at 10:15:31PM +0000, Alan Cox wrote:
> gcc is a *LOT* smarter than you give it credit for. It will not warn for
> cases where it isn't able to tell how foo is used passed with &foo. It
> will warn for cases where it can

static inline __attribute__((always_inline)) int bar(int n, int *idx)
{
        if (n != 1) 
                return 0; 
        *idx = 1;
        return 1;  
}
void baz(int *v, int n)
{
        int idx;
        int p = bar(n, &idx);
        if (__builtin_expect(!p, 0))
                return; 
        *v |= idx;
}

and try gcc -Wall on that.  Watch it warn about idx being possibly
uninitialized.  Replace __builtin_expect(!p, 0) with !p and see
the warning go away.  That, BTW, is a trimmed-down source of bogus
warning in bio.c.  And a lot of its analogs all over the tree.

Re: 2.6.14 assorted warnings

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 1290 bytes --]

Also, this test case:

------------------------------------------------------------
extern int f1(void);

static unsigned char f2(unsigned int *def)
{
	if (!f1())
		return 0;
	*def = 1;
	return 1;
}

unsigned char f3(unsigned char **eoc)
{
	unsigned int def;

	if (!f2(&def))
		return 0;
	if (def)
		*eoc = (unsigned char *)1;
	else
		*eoc = 0;
	return 1;
}

static int f4(unsigned int *def)
{
	if (!f1())
		return 0;
	*def = 1;
	return 1;
}

unsigned char f5(unsigned char **eoc)
{
	unsigned int def;

	if (!f4(&def))
		return 0;
	if (def)
		*eoc = (unsigned char *)1;
	else
		*eoc = 0;
	return 1;
}
------------------------------------------------------------

compiled with "gcc -Wall -O2" gives:
xx.c: In function 'f3':
xx.c:14: warning: 'def' may be used uninitialized in this function

but doesn't complain about the same code in f5.  The difference is that
f4 returns "int" while f2 returns "unsigned char".  This has apparently
been fixed in gcc mainline - the above comes from Debian unstables' gcc
(4.0.3 20051023 (prerelease) (Debian 4.0.2-3)).

Compiling with "gcc -Wall -O2 -fnoinline" suppresses the warning.

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]

Re: 2.6.14 assorted warnings

[Al Viro]

On Sun, Oct 30, 2005 at 10:25:43PM +0000, Al Viro wrote:
> static inline __attribute__((always_inline)) int bar(int n, int *idx)
> {
>         if (n != 1) 
>                 return 0; 
>         *idx = 1;
>         return 1;  
> }
> void baz(int *v, int n)
> {
>         int idx;
>         int p = bar(n, &idx);
>         if (__builtin_expect(!p, 0))
>                 return; 
>         *v |= idx;
> }
> 
> and try gcc -Wall on that.

Duh.  gcc -Wall -Os, of course

Re: 2.6.14 assorted warnings

[Paul Mackerras]

Alan Cox writes:

> gcc is a *LOT* smarter than you give it credit for. It will not warn for
> cases where it isn't able to tell how foo is used passed with &foo. It
> will warn for cases where it can

Gcc thinks it is a lot smarter than it actually is, in fact. :)

The usual case where it gives a bogus warning is where the value of
one variable is correlated with the defined-ness of another, for
example:

	found = 0;
	for (i = 0; i < N; ++i) {
		if (a[i] == foo) {
			x = b[i];
			found = 1;
			break;
		}
	}
	if (found)
		bar(x);

Gcc will warn on the use of x when in fact it is perfectly OK, and we
get quite a few of these in compiling a kernel.  At a minimum, I would
like to be able to disable the "may be used uninitialized" warnings
while still getting the "is used uninitialized" warnings.

Paul.

Re: 2.6.14 assorted warnings

[Al Viro]

On Mon, Oct 31, 2005 at 11:53:27AM +1100, Paul Mackerras wrote:
> Gcc will warn on the use of x when in fact it is perfectly OK, and we
> get quite a few of these in compiling a kernel.  At a minimum, I would
> like to be able to disable the "may be used uninitialized" warnings
> while still getting the "is used uninitialized" warnings.

Quite.  "may be used uninitialized" has _way_ too low S/N ratio - absolute
majority of these warnings are bogus.  Moreover, several very common use
patterns reliably trigger them.