Hello,
the program below gives a warning with some versions of gcc.
I tried with 4.3.4, 4.4.2 (debian versions) and 4.5.0 (snapshot, compiled
myself today). Some people told me that 4.2.4, 4.2.1 and 3.4.6 don't warn.
4.5.0 outputs:
#‘ssa_name’ not supported by pp_c_expression#]’kr-1-17.c: In function ‘main’:
kr-1-17.c:12:10: warning: may be used uninitialized in this function
4.4.2 / 4.3.4 output:
kr-1-17.c: In function ‘main’:
kr-1-17.c:12: warning: ‘line[0]’ may be used uninitialized in this function
I believe that the warning is a false positive: the first `if' condition can
only be true after the second `if' condition was true, but then line[0] is set.
---------------
program in question:
/* print all lines longer than LEN chars */
/* #include <stdio.h> */
#define EOF (-1)
int getchar(void);
int putchar(int c);
#define LEN 1
int main(void)
{
char line[LEN];
int c, i = 0;
while(EOF != (c = getchar())) {
if(i == LEN) for(i = 1; i <= LEN; ++i) putchar(line[i - 1]);
if(i < LEN) line[i++] = c; else putchar(c);
if(c == '\n') i = 0;
}
return 0;
}
------------------
4.4.2 debug output:
$ gcc -v -save-temps -std=c99 -Wall -Wextra -pedantic -O2 -o kr-1-17 kr-1-17.c
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.2-8'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-targets=all --with-arch-32=i486 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.2 (Debian 4.4.2-8)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic' '-march=i486'
/usr/lib/gcc/i486-linux-gnu/4.4.2/cc1 -E -quiet -v kr-1-17.c -mtune=generic
-march=i486 -std=c99 -Wall -Wextra -pedantic -O2 -fpch-preprocess -o kr-1-17.i
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../i486-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/lib/gcc/i486-linux-gnu/4.4.2/include
/usr/lib/gcc/i486-linux-gnu/4.4.2/include-fixed
/usr/include/i486-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic' '-march=i486'
/usr/lib/gcc/i486-linux-gnu/4.4.2/cc1 -fpreprocessed kr-1-17.i -quiet
-dumpbase kr-1-17.c -mtune=generic -march=i486 -auxbase kr-1-17 -O2 -Wall
-Wextra -pedantic -std=c99 -version -o kr-1-17.s
GNU C (Debian 4.4.2-8) version 4.4.2 (i486-linux-gnu)
compiled by GNU C version 4.4.2, GMP version 4.3.1, MPFR version
2.4.2-p1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: aac48a8fc76155c3bd92bf60f31a771c
kr-1-17.c: In function ‘main’:
kr-1-17.c:12: warning: ‘line[0]’ may be used uninitialized in this function
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic' '-march=i486'
as -V -Qy -o kr-1-17.o kr-1-17.s
GNU assembler version 2.20 (i486-linux-gnu) using BFD version (GNU Binutils for
Debian) 2.20
COMPILER_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/4.4.2/:/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic' '-march=i486'
/usr/lib/gcc/i486-linux-gnu/4.4.2/collect2 --build-id --eh-frame-hdr -m
elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o kr-1-17
/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../lib/crt1.o
/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../lib/crti.o
/usr/lib/gcc/i486-linux-gnu/4.4.2/crtbegin.o
-L/usr/lib/gcc/i486-linux-gnu/4.4.2 -L/usr/lib/gcc/i486-linux-gnu/4.4.2
-L/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.4.2/../../.. kr-1-17.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/i486-linux-gnu/4.4.2/crtend.o
/usr/lib/gcc/i486-linux-gnu/4.4.2/../../../../lib/crtn.o
-------------
4.5.0 debug output:
$ gcc/bin/gcc -v -save-temps -std=c99 -Wall -Wextra -pedantic -O2 -o kr-1-17
kr-1-17.c
Using built-in specs.
COLLECT_GCC=gcc/bin/gcc
COLLECT_LTO_WRAPPER=/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../gcc-4.5-20091231/configure --prefix=/home/foo/gcc
Thread model: posix
gcc version 4.5.0 20091231 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic'
/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/cc1 -E -quiet -v kr-1-17.c
-mtune=generic -std=c99 -Wall -Wextra -pedantic -O2 -fpch-preprocess -o
kr-1-17.i
ignoring nonexistent directory
"/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/home/foo/gcc/include
/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/include
/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic'
/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/cc1 -fpreprocessed kr-1-17.i
-quiet -dumpbase kr-1-17.c -mtune=generic -auxbase kr-1-17 -O2 -Wall -Wextra
-pedantic -std=c99 -version -o kr-1-17.s
GNU C (GCC) version 4.5.0 20091231 (experimental) (i686-pc-linux-gnu)
compiled by GNU C version 4.5.0 20091231 (experimental), GMP version
4.3.1, MPFR version 2.4.2-p1, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU C (GCC) version 4.5.0 20091231 (experimental) (i686-pc-linux-gnu)
compiled by GNU C version 4.5.0 20091231 (experimental), GMP version
4.3.1, MPFR version 2.4.2-p1, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 38ffc6560b371289af74b2eb597e08f5
#‘ssa_name’ not supported by pp_c_expression#]’kr-1-17.c: In function ‘main’:
kr-1-17.c:12:10: warning: may be used uninitialized in this function
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic'
as -V -Qy --32 -o kr-1-17.o kr-1-17.s
GNU assembler version 2.20 (i486-linux-gnu) using BFD version (GNU Binutils for
Debian) 2.20
COMPILER_PATH=/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/:/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/:/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/:/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/:/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/
LIBRARY_PATH=/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/:/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c99' '-Wall' '-Wextra' '-pedantic'
'-O2' '-o' 'kr-1-17' '-mtune=generic'
/home/foo/gcc/libexec/gcc/i686-pc-linux-gnu/4.5.0/collect2 --eh-frame-hdr -m
elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o kr-1-17 /usr/lib/crt1.o
/usr/lib/crti.o /home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/crtbegin.o
-L/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0
-L/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/../../.. kr-1-17.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/home/foo/gcc/lib/gcc/i686-pc-linux-gnu/4.5.0/crtend.o /usr/lib/crtn.o
----------
kr-1-17.i
# 1 "kr-1-17.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "kr-1-17.c"
int getchar(void);
int putchar(int c);
int main(void)
{
char line[1];
int c, i = 0;
while((-1) != (c = getchar())) {
if(i == 1) for(i = 1; i <= 1; ++i) putchar(line[i - 1]);
if(i < 1) line[i++] = c; else putchar(c);
if(c == '\n') i = 0;
}
return 0;
}
Thanks in advance; I hope it's not a duplicate :-)
Regards
Joern Heissler
--
Summary: warning: ‘line[0]’ may be used uninitialized in this
function
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gccbugs at joern dot heissler dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42636
