Re: [Crash-utility] [PATCH] GDB: fix completion related libstdc++ assert

-----Original Message----- > > > +--- gdb-10.2/gdb/ada-lang.c.orig > > > ++++ gdb-10.2/gdb/ada-lang.c > > > +@@ -997,7 +997,7 @@ ada_fold_name (gdb::string_view name) > > > + int len = name.size (); > > > + GROW_VECT (fold_buffer, fold_buffer_size, len + 1); > > > + > > > +- if (name[0] == '\'') > > > ++ if (name.size () > 0 && name[0] == '\'') > > > + { > > > + strncpy (fold_buffer, name.data () + 1, len - 2); > > > + fold_buffer[len - 2] = '\000'; > > > +@@ -1006,7 +1006,7 @@ ada_fold_name (gdb::string_view name) > > > + { > > > + int i; > > > + > > > +- for (i = 0; i <= len; i += 1) > > > ++ for (i = 0; i < len; i++) > > > + fold_buffer[i] = tolower (name[i]); > > > > According to 2ccee230f830 ("Fix off-by-one error in ada_fold_name"), > > please add this: > > > > + fold_buffer[i] = '\0'; > > > > > > > > No, the above change will definitely cause a core dump because it assigns the value '\0' to a > null pointer > > when the name string is null. > > Hmm, I'm not familiar with gdb source, could you explain a little more? > The following is the function with your patch. > > static char * > ada_fold_name (gdb::string_view name) > { > static char *fold_buffer = NULL; > static size_t fold_buffer_size = 0; > > int len = name.size (); > GROW_VECT (fold_buffer, fold_buffer_size, len + 1); > > if (name.size () > 0 && name[0] == '\'') > { > strncpy (fold_buffer, name.data () + 1, len - 2); > fold_buffer[len - 2] = '\000'; > } > else > { > int i; > > for (i = 0; i < len; i++) > fold_buffer[i] = tolower (name[i]); > } > > return fold_buffer; > } > > The GROW_VECT() looks to alloc 1 byte to fold_buffer if name.size() is zero. > > > > Theoretically yes, but you could notice that the definition of 'fold_buffer_size', actually it is a static > variable, the ada_fold_name() may be called many times, but variable 'fold_buffer_size' is only initialized > to zero once, it means that the value of 'fold_buffer_size' may not be zero(>1) in the subsequent calls. > For this case, the GROW_VECT() will never allocate new memory. Thanks, but I noticed that the fold_buffer is also a static variable, it looks like once it's allocated, never be freed. So it always has 1 byte at least?

Kazu > > See the definition of GROW_VECT(): > > #define GROW_VECT(v, s, m) \ > if ((s) < (m)) (v) = (char *) grow_vect (v, &(s), m, sizeof *(v)); > > /* Assuming VECT points to an array of *SIZE objects of size > ELEMENT_SIZE, grow it to contain at least MIN_SIZE objects, > updating *SIZE as necessary and returning the (new) array. */ > > static void * > grow_vect (void *vect, size_t *size, size_t min_size, int element_size) > { > if (*size < min_size) > { > *size *= 2; > if (*size < min_size) > *size = min_size; > vect = xrealloc (vect, *size * element_size); > } > return vect; > } > > > Hope this helps. > > Thanks > Lianbo > > > Then len is zero, and nothing is done in the for loop, and fold_buffer[i] > (== fold_buffer[0]) can be set '\0', I thought. > > > + fold_buffer[i] = '\0'; > > And as far as I've tried, no abort occured. > > Thanks, > Kazu > >