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bork strcpy() in glibc-2.12.1 + core i7 + x86_64
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s4e8
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Joined: 29 Jul 2006
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PostPosted: Fri Aug 20, 2010 1:57 am    Post subject: bork strcpy() in glibc-2.12.1 + core i7 + x86_64 Reply with quote

Following code output "12345688" instead "12345678".
Code:

int main(){
        char buf[80];
        strcpy(buf, "012345678\n");
        strcpy(buf, buf+1);
        puts(buf);
        return 0;
}

add --disable-multi-arch to ebuild, disable all SSE optimizations, and problem gone.
This bug cause bash generate wrong \W prompt string.
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EatMeerkats
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Joined: 15 Mar 2006
Posts: 234

PostPosted: Fri Aug 20, 2010 2:33 am    Post subject: Reply with quote

From the strcpy man page:
Code:
The source and destination strings should not overlap, as the behavior is undefined.

Bash does this kind of strcpy?

EDIT: Oops, that was from OS X's man page (wrong window). I would think the same applies to Linux, though, unless something is specifically done to handle this case (like memmove does).
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Etal
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PostPosted: Fri Aug 20, 2010 2:59 am    Post subject: Reply with quote

Copying overlapped strings is a definite no-no. Both the POSIX standard and the glibc manual state that the behavior is undefined:

man 3p strcpy:
DESCRIPTION
       The strcpy() function shall copy the string pointed to by s2 (including the terminating null byte)
       into the array pointed to by s1. If copying takes place between objects that overlap, the behavior
       is undefined.

info libc 'Copying and Concatenation':
  -- Function: char * strcpy (char *restrict TO, const char *restrict
           FROM)
      This copies characters from the string FROM (up to and including
      the terminating null character) into the string TO.  Like
      `memcpy', this function has undefined results if the strings
      overlap.  The return value is the value of TO.


If you found this flaw in bash, you should definitely report it.
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s4e8
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Posts: 309

PostPosted: Fri Aug 20, 2010 3:28 am    Post subject: Reply with quote

both bash and syslogd use this kind of code...
this is from bash
Code:

                        t = strrchr (t_string, '/');
                        if (t)
                          strcpy (t_string, t + 1);

syslogd use following method deal with continuation line
LINE1;\
strip backslash
LINE1;
read next line
LINE1;<IDENT>LINE2
strcpy to strip ident spaces...
LINE1;LINE2
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xibo
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Joined: 21 Aug 2007
Posts: 152
Location: moving between kubuntu and ubuntu kde edition

PostPosted: Fri Aug 20, 2010 5:36 am    Post subject: Reply with quote

s4e8 wrote:
this is from bash
Code:

                        t = strrchr (t_string, '/');
                        if (t)
                          strcpy (t_string, t + 1);

tell them to use bcopy then, or put "-Dstrcpy(a,b)=bcopy(a,b,strlen(b)+1)" to your CFLAGS when compiling it.
string.h wrote:
extern char *strcpy (char *__restrict __dest, __const char *__restrict __src)
__THROW __nonnull ((1, 2));

guess what __restrict means ( or look the references to the man page posted above )...

EDIT: just found the refered bash code section in $SRC_DIR/y.tab.c:7484. On top of that, a wonderful use of goto to get to the end of the switch statement in every case, too 8O
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