[patch] libiberty/vasprintf.c bug

[patch] libiberty/vasprintf.c bug

[qinwei]

Dears, problems are here:

#include<stdio.h>
class student 
{
public:
  student(int age)
  {
    m_age = age;
  }
  void  ShowAge()
  {
    printf("%d",m_age);
  }
protected:
  int m_age;
};
int main(void)
{
  student aa(10); 
  aa.ShowAge();
  return 0;
}

build it with score-elf-gcc (gcc-4.2), 
and debug it with score-elf-gdb (gdb-6.6 release version),

(gdb) b 12
Breakpoint 1 at 0x196: file main.cxx, line 12.
(gdb) r
Starting program: /home/qinwei/GJ283/code/build_linux/debug-gdb/tt 

Breakpoint 1, student::ShowAge (this=0x7ffffd8) at main.cxx:12
12          printf("%d",m_age);
(gdb) p this.ShowAge()
Cannot resolve method (null)ShowAge to any overloaded instance
(gdb)

When type "p this.ShowAge()", gdb (linux-version) will call function
"error" which will call "vasprintf" in glibc and print this error
message correctly. 
But using mingw-build gdb, this case will cause segmentation fault.
For mingw-build gdb will use "vasprintf" in libiberty/vasprintf.c
which has bug. Modify this can solve the problem.

diff -ruN vasprintf.c vasprintf.c.new &>vasprintf.c.patch
--- vasprintf.c 2007-03-22 16:03:13.000000000 +0800
+++ vasprintf.c.new 2007-03-13 11:50:27.000000000 +0800
@@ -64,6 +64,7 @@
 int_vasprintf (char **result, const char *format, va_list args)
 {
   const char *p = format; 
+  char *ptr = NULL; 
   /* Add one to make sure that it is never zero, which might cause malloc
      to return NULL.  */
   int total_width = strlen (format) + 1;
@@ -125,7 +126,8 @@
          total_width += 307; 
          break; 
        case 's':
-         total_width += strlen (va_arg (ap, char *));
+          if ((ptr = va_arg (ap, char *)) != NULL) 
+           total_width += strlen (ptr);
          break; 
        case 'p':
        case 'n':

Best regards,
Qinwei
Mail  qinwei@sunnorth.com.cn
Phone +86-010-62981668-2708
Fax   +86-010-62985972

Re: [patch] libiberty/vasprintf.c bug

[DJ Delorie]

If ptr is NULL, shouldn't we add strlen("(null)") ?

Re: [patch] libiberty/vasprintf.c bug

[qinwei]

 > If ptr is NULL, shouldn't we add strlen("(null)") ?

Yes. This will cause error.

const char *p = NULL;
int i = strlen (p);

Re: [patch] libiberty/vasprintf.c bug

[DJ Delorie]

>  > If ptr is NULL, shouldn't we add strlen("(null)") ?
> 
> Yes. This will cause error.

> const char *p = NULL;
> int i = strlen (p);

I understand that.  My question was, if you printf("%s", NULL), what
happens?  If it prints "(null)", does that mean you need to account
for the length of that string in your calculations?

(also, note that libiberty patches go to gcc-patches@gcc.gnu.org, in
addition to any other lists who might be interested)