c - fread(), solaris to unix portability and use of uninitialised values -

valgrind found following error , i, after reading documentation, code , other questions in here couldn't figure out why.

valgrind: first warning

~$ valgrind --vgdb=yes --vgdb-error=0 --read-var-info=yes --leak-check=yes --track-origins=yes debitadmin*

debitadmin  ==20720== conditional jump or move depends on uninitialised value(s) ==20720==    @ 0x4013bc6: initialise (dbg.c:199) ==20720==    0x4013f5c: ??? (in /opt/ivb/lib/libdbg.so) ==20720==    0x4013917: ??? (in /opt/ivb/lib/libdbg.so) ==20720==    0x5f5ffe: _dl_init (in /lib/ld-2.12.so) ==20720==    0x5e788e: ??? (in /lib/ld-2.12.so) ==20720==  uninitialised value created stack allocation ==20720==    @ 0x4013a8f: initialise (dbg.c:150) 

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gdb & valgrind: symbols

(gdb) info symbol 0x4013a8f initialise + 5 in section .text of /opt/ivb/lib/libdbg.so  (gdb) info symbol 0x4013bc6 initialise + 316 in section .text of /opt/ivb/lib/libdbg.so 

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code: dbg.c

148    void 149    initialise(void) 150    { 151        register int = 0; 152        char buffer[filename_max] = ""; 153        char *program = null; 154        struct sigaction act = {0}; ... ...  195         while ( ! feof(proc_file) && ! ferror(proc_file)) 196         { 197             char ch; 198             fread(&ch,1,1,proc_file); 199             if ( ch != 0 ) 200             fprintf(stderr,"%c",ch); 201             else 202             fprintf(stderr," "); 203         } 

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gdb: backtrace

(gdb) bt #0  0x04013bc6 in initialise () @ dbg.c:199 #1  0x04013f5d in __do_global_ctors_aux () /opt/ivb/lib/libdbg.so #2  0x04013918 in _init () /opt/ivb/lib/libdbg.so #3  0x005f5fff in _dl_init_internal () /lib/ld-linux.so.2 #4  0x005e788f in _dl_start_user () /lib/ld-linux.so.2 

gdb: locals

(gdb) info locals ch = 0 '\000' c = 10 

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extra information

• this code part of library, ported solaris unix

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what understood:

valgrind complains

char ch;  

is not initialised, after

fread(&ch,1,1,proc_file); 

after checking gdb ch value after above line, have:

ch = 0 '\000' 

proc_file does't correspond that, can see:

(gdb) print *proc_file $17 = {   _flags = -72538984,    _io_read_ptr = 0x4352000 "debitadmin",    _io_read_end = 0x4352000 "debitadmin",    _io_read_base = 0x4352000 "debitadmin",    _io_write_base = 0x4352000 "debitadmin",    _io_write_ptr = 0x4352000 "debitadmin",    _io_write_end = 0x4352000 "debitadmin",    _io_buf_base = 0x4352000 "debitadmin",    _io_buf_end = 0x4353000 <address 0x4353000 out of bounds>,    _io_save_base = 0x0,    _io_backup_base = 0x0,    _io_save_end = 0x0,    _markers = 0x0,    _chain = 0x79c580,    _fileno = 3,    _flags2 = 0,    _old_offset = 0,    _cur_column = 0,    _vtable_offset = 0 '\000',    _shortbuf = "",    _lock = 0x43dc0c0,    _offset = -1,    __pad1 = 0x0,    __pad2 = 0x43dc0cc,    __pad3 = 0x0,    __pad4 = 0x0,    __pad5 = 0,    _mode = -1,    _unused2 = '\000' <repeats 39 times> } 

there no mcve because i'm still not sure problem is, i'm counting on experts me tackle that.

so, question is, why ch empty after fread() assignment? portability issue between solaris , linux? problem or missing something?

update: file has been opened , checked not null.

#elif linux     {         char name[filename_max];     file *proc_file;     sprintf(name,"/proc/%d/cmdline",(int)getpid());     proc_file=fopen (name,"r");     if ( proc_file != null )     {         int c;         /* read in programs name */         for(c=0; ((fread(&buffer[c],1,1,proc_file)== 1) && (buffer[c]!=0)); c++);          /* print out program */         (void)fprintf(stderr,"%s ", buffer);          /* , program arguments , not efficient works....*/         fprintf(stderr," ");         while ( ! feof(proc_file) && ! ferror(proc_file))         {             char ch;             test *t;             t = fread(&ch,1,1,proc_file);             if ( ch != 0 )             fprintf(stderr,"%c",ch);             else             fprintf(stderr," ");         }         (void) fprintf(stderr,"\n\n");     }     } #endif 

q 1. why ch empty after fread() assignment?

(most probably) because fread() failed. see detailed answer below.

q 2.is portability issue between solaris , linux?

no, there possible issue code itself, correctly reported valgrind.

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i cannot quite tell below approach solve problem, should consider below points improve code, e.g.,

• point 1: check return value of fread() ensure sucess. if fread() failure, using ch later invoke read-before-write scenario. ch automatic local variable , not initialized explicitly, invoke undefined behaviour.

• point 2: read : why while ( !feof (file) ) (almost) wrong?