[Bug c/35903] New: false warning when passing quoted string to function strcmp(arg,"no");

[Bug c/35903] New: false warning when passing quoted string to function strcmp(arg,"no");

[rsa at us dot ibm dot com]

When building libm-test.c (part of the GLIBC make check math test suite for
GLIBC CVS head as of April 10, 2008) with GCC 4.3 I get the following warning:

math/libm-test.c: In function 'parse_opt':
math/libm-test.c:6102: warning: array subscript is above array bounds

In relation to the following code:

      if (strcmp (arg, "yes") == 0)

This warning goes away if replaced with:
      char yes[] = "yes";
      if (strcmp (arg,yes) == 0)

Andrew Pinski says this is a false warning and that I should file a bug report.


-- 
           Summary: false warning when passing quoted string to function
                    strcmp(arg,"no");
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rsa at us dot ibm dot com
 GCC build triplet: n/a
  GCC host triplet: n/a
GCC target triplet: n/a


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug c/35903] false warning when passing quoted string to function strcmp(arg,"no");

[rsa at us dot ibm dot com]

------- Comment #1 from rsa at us dot ibm dot com  2008-04-10 18:57 -------
Created an attachment (id=15465)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15465&action=view)
preprocessed test-ildouble.c file.

strcmp on line 16036 seems to be the problematic one.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug c/35903] false warning when passing quoted string to function strcmp(arg,"no");

[rsa at us dot ibm dot com]

------- Comment #2 from rsa at us dot ibm dot com  2008-04-10 18:58 -------
Compiled with:
cd /home/ryanarn/glibc/stages/stage_lround/glibc/math

/opt/at43/bin/gcc -m32 test-ildoubl.c -save-temps -c -std=gnu99 -fgnu89-inline
-O2 -Wall -Winline -Wwrite-strings -fmerge-all-constants -g -mcpu=power4
-mlong-double-128 -mnew-mnemonics -Wstrict-prototypes -mlong-double-128   
-Wno-uninitialized -D__NO_MATH_INLINES -D__LIBC_INTERNAL_MATH_INLINES
-I../include
-I/home/ryanarn/glibc/stages/stage_lround/build/glibc32_power4/math
-I/home/ryanarn/glibc/stages/stage_lround/build/glibc32_power4
-I../sysdeps/powerpc/powerpc32/elf -I../sysdeps/powerpc/elf
-I../sysdeps/unix/sysv/linux/powerpc/powerpc32/power4/fpu
-I../sysdeps/powerpc/powerpc32/power4/fpu
-I../sysdeps/unix/sysv/linux/powerpc/powerpc32/power4
-I../sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu
-I../sysdeps/powerpc/powerpc32/fpu
-I../nptl/sysdeps/unix/sysv/linux/powerpc/powerpc32
-I../sysdeps/unix/sysv/linux/powerpc/powerpc32
-I../nptl/sysdeps/unix/sysv/linux/powerpc -I../sysdeps/unix/sysv/linux/powerpc
-I../sysdeps/ieee754/ldbl-128ibm -I../sysdeps/ieee754/ldbl-opt
-I../nptl/sysdeps/unix/sysv/linux -I../nptl/sysdeps/pthread
-I../sysdeps/pthread -I../sysdeps/unix/sysv/linux -I../sysdeps/gnu
-I../sysdeps/unix/common -I../sysdeps/unix/mman -I../sysdeps/unix/inet
-I../nptl/sysdeps/unix/sysv -I../sysdeps/unix/sysv -I../sysdeps/unix/powerpc
-I../nptl/sysdeps/unix -I../sysdeps/unix -I../sysdeps/posix
-I../sysdeps/powerpc/powerpc32/power4 -I../sysdeps/powerpc/powerpc32
-I../sysdeps/wordsize-32 -I../sysdeps/powerpc/fpu -I../sysdeps/powerpc/math
-I../nptl/sysdeps/powerpc -I../sysdeps/powerpc -I../sysdeps/ieee754/dbl-64
-I../sysdeps/ieee754/flt-32 -I../sysdeps/ieee754 -I../sysdeps/generic/elf
-I../sysdeps/generic -I../nptl  -I.. -I../libio -I. -nostdinc -isystem
/opt/at43/lib/gcc/powerpc64-linux/4.3.0/include -isystem
/opt/at43/lib/gcc/powerpc64-linux/4.3.0/include-fixed -isystem /usr/include
-D_LIBC_REENTRANT -include ../include/libc-symbols.h   -DNOT_IN_libc=1
-U__LIBC_INTERNAL_MATH_INLINES -D__FAST_MATH__ -DTEST_FAST_MATH -fno-builtin  
-o
/home/ryanarn/glibc/stages/stage_lround/build/glibc32_power4/math/test-ildoubl.o
-MD -MP -MF
/home/ryanarn/glibc/stages/stage_lround/build/glibc32_power4/math/test-ildoubl.o.dt
-MT
/home/ryanarn/glibc/stages/stage_lround/build/glibc32_power4/math/test-ildoubl.o


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false warning when passing quoted string to function strcmp(arg,"no");

[cepeda at gmail dot com]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 4462 bytes --]



------- Comment #3 from cepeda at gmail dot com  2009-10-16 16:51 -------
This bug has no changed for months, I think it is still active.

It seems not to work only when size of char[] is 3 (2+'\0'). A test case is
this:
// Begin of code
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
   printf("%d",strcmp(argv[0],"A")); //  NO warning
   printf("%d",strcmp(argv[0],"AA")); //  warning: array subscript
   printf("%d",strcmp(argv[0],"AAA")); //  NO warning
   return 0;
}
// End of code


The compilation says:

$ gcc -v -save-temps -O3 -fno-builtin -funsigned-char  -Wall test.c
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu8'
--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 --disable-werror --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 4.4.1 (Ubuntu 4.4.1-4ubuntu8) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-fno-builtin' '-funsigned-char'
'-Wall' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.1/cc1 -E -quiet -v test.c -D_FORTIFY_SOURCE=2
-mtune=generic -march=i486 -Wall -fno-builtin -funsigned-char -O3
-fpch-preprocess -fstack-protector -o test.i
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.4.1/include
 /usr/lib/gcc/i486-linux-gnu/4.4.1/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-fno-builtin' '-funsigned-char'
'-Wall' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.1/cc1 -fpreprocessed test.i -quiet -dumpbase
test.c -mtune=generic -march=i486 -auxbase test -O3 -Wall -version -fno-builtin
-funsigned-char -fstack-protector -o test.s
GNU C (Ubuntu 4.4.1-4ubuntu8) version 4.4.1 (i486-linux-gnu)
        compiled by GNU C version 4.4.1, GMP version 4.3.1, MPFR version
2.4.1-p2.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 293503c4ddf766b61fc5ff6a5ff38cdc
test.c: In function ‘main’:
test.c:7: warning: array subscript is above array bounds
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-fno-builtin' '-funsigned-char'
'-Wall' '-mtune=generic' '-march=i486'
 as -V -Qy -o test.o test.s
GNU assembler version 2.19.92 (i486-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.19.92.20091014
COMPILER_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/:/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../:/lib/:/usr/lib/:/usr/lib/i486-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-fno-builtin' '-funsigned-char'
'-Wall' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.1/collect2 --build-id --eh-frame-hdr -m
elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -z relro
/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o
/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crti.o
/usr/lib/gcc/i486-linux-gnu/4.4.1/crtbegin.o
-L/usr/lib/gcc/i486-linux-gnu/4.4.1 -L/usr/lib/gcc/i486-linux-gnu/4.4.1
-L/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.4.1/../../..
-L/usr/lib/i486-linux-gnu test.o -lgcc --as-needed -lgcc_s --no-as-needed -lc
-lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/i486-linux-gnu/4.4.1/crtend.o
/usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crtn.o


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false warning when passing quoted string to function strcmp(arg,"no");

[manu at gcc dot gnu dot org]

------- Comment #4 from manu at gcc dot gnu dot org  2009-10-17 11:03 -------
(In reply to comment #3)
> This bug has no changed for months, I think it is still active.

Newer higher priority bugs often make us forget about old inactive bugs. Going
through old bugs and testing whether they still exist in a recent GCC would be
extremely helpful.

> It seems not to work only when size of char[] is 3 (2+'\0'). A test case is
> this:

Could you produce a preprocessed testcase? Is the printf needed? If not, please
take it and stdio.h out of the testcase to make it even simpler.

http://gcc.gnu.org/bugs/#need


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false warning when passing quoted string to function strcmp(arg,"no");

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2009-10-22 17:56 -------
@Alfonso,

We need the preprocessed testcase. See my previous comment.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false warning when passing quoted string to function strcmp(arg,"no");

[cepeda at gmail dot com]

------- Comment #6 from cepeda at gmail dot com  2009-10-22 18:30 -------
Created an attachment (id=18870)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18870&action=view)
Preprocessed file of the testcase


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false warning when passing quoted string to function strcmp(arg,"no");

[cepeda at gmail dot com]

------- Comment #7 from cepeda at gmail dot com  2009-10-22 18:31 -------
Unfortunately and surprisely, printf is needed in this testcase. I think that a
different testcase without the printf can be found because the bigger code that
I used had not got the printf.

I have attatched the preproccessed testcase.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false uninitialized warning when passing quoted string to function strcmp(arg,"no");

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-01-02 19:24 -------
Similar to PR35392 this only happens with -funsigned-char, thus these may
as well be dups.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |35392
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-01-02 19:24:39
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false Warray-bounds warning when passing quoted string to function strcmp(arg,"no");

[manu at gcc dot gnu dot org]

------- Comment #9 from manu at gcc dot gnu dot org  2010-02-19 23:56 -------
This is not an uninitialized issue. 

The reason this requires -O2 is that -Warray-bounds requires VRP to warn. The
gimple output already looks quite different.

-funsigned-char:

       <D.1565>:
        [pr35903.i : 309:15] D.1567 = __s1D.796 + 3;
        [pr35903.i : 309:15] D.1568 = [pr35903.i : 309] *D.1567;
        [pr35903.i : 310:11] D.1569 = (intD.0) D.1568;
        [pr35903.i : 318:12] D.1570 = [pr35903.i : 311] &[pr35903.i : 311]
"AA"[0] + 3;
        [pr35903.i : 318:12] D.1571 = [pr35903.i : 318] *D.1570;
        [pr35903.i : 310:11] D.1572 = (intD.0) D.1571;
        [pr35903.i : 308:10] __resultD.797 = D.1569 - D.1572;
        <D.1566>:
        <D.1556>:

-fsigned-char

     <D.1566>:
        [pr35903.i : 309:15] D.1568 = __s1D.796 + 3;
        [pr35903.i : 309:15] D.1569 = [pr35903.i : 309] *D.1568;
        [pr35903.i : 310:11] D.1570 = (intD.0) D.1569;
        [pr35903.i : 311:12] D.1540 = (const unsigned charD.10 *) [pr35903.i :
318] "AA";
        [pr35903.i : 318:12] D.1571 = D.1540 + 3;
        [pr35903.i : 318:12] D.1572 = [pr35903.i : 318] *D.1571;
        [pr35903.i : 310:11] D.1573 = (intD.0) D.1572;
        [pr35903.i : 308:10] __resultD.797 = D.1570 - D.1573;
        <D.1567>:
        <D.1557>:
        <D.1547>:


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|24639                       |
              nThis|                            |
            Summary|false uninitialized warning |false Warray-bounds warning
                   |when passing quoted string  |when passing quoted string
                   |to function                 |to function
                   |strcmp(arg,"no");           |strcmp(arg,"no");


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903

[Bug middle-end/35903] false Warray-bounds warning when passing quoted string to function strcmp(arg,"no");

[manu at gcc dot gnu dot org]

------- Comment #10 from manu at gcc dot gnu dot org  2010-02-20 00:19 -------
Reduced testcase:

extern int strlen (__const char *__s);
int echo (int);
int main(int argc, char **argv)
{
  echo (({ int __s1_len, __s2_len;
  (__builtin_constant_p (argv[0]) && __builtin_constant_p ("AA") &&
   (__s1_len = strlen (argv[0]), __s2_len = strlen ("AA"),
    (!((int)(const void *)((argv[0]) + 1) - (int)(const void *)(argv[0]) == 1)
     || __s1_len >= 4)
    &&
    (!((int)(const void *)(("AA") + 1) - (int)(const void *)("AA") == 1)
     || __s2_len >= 4))
   ? 1
   : (__builtin_constant_p (argv[0])
      && ((int)(const void *)((argv[0]) + 1) - (int)(const void *)(argv[0]) ==
1)
      && (__s1_len = strlen (argv[0]), __s1_len < 4)
      ? 1
      : (__builtin_constant_p ("AA") && ((int)(const void *)(("AA") + 1) -
(int)(const void *)("AA") == 1)
         && (__s2_len = strlen ("AA"), __s2_len < 4)
         ? (__builtin_constant_p (argv[0])
            && ((int)(const void *)((argv[0]) + 1) - (int)(const void
*)(argv[0]) == 1)
            ? 1
            : (({
              __const unsigned char *__s1 = (__const unsigned char *) (__const
char *) (argv[0]);
              register int __result = __s1[0] - ((__const unsigned char *)
(__const char *) ("AA"))[0];
              if (__s2_len > 0 && __result == 0)
                {
                  __result = (__s1[1] - ((__const unsigned char *) (__const
char *) ("AA"))[1]);
                  if (__s2_len > 1 && __result == 0)
                    {
                      __result = (__s1[2] - ((__const unsigned char *) (__const
char *) ("AA"))[2]);
                      if (__s2_len > 2 && __result == 0)
                        __result = (__s1[3] - ((__const  unsigned  char  *)
(__const  char  *) ("AA"))[3]);
                    }
                }
              __result;
            })))
         : 0))); }));

  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903