[PATCH] Avoid indexing std::vector past the end

[PATCH] Avoid indexing std::vector past the end

[Ruslan Kabatsayev]

The code here wants to find address of an element, and often this
element is one past the end of std::vector. Dereferencing that element
leads to undefined behavior, so it's better to simply use pointer
arithmetic instead of taking address of invalid dereference.

gdb/ChangeLog:

	* psymtab.c (recursively_search_psymtabs): Use pointer arithmetic
	instead of dereferencing std::vector past the end.
---
 gdb/psymtab.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/gdb/psymtab.c b/gdb/psymtab.c
index c87ef25..c622f4c 100644
--- a/gdb/psymtab.c
+++ b/gdb/psymtab.c
@@ -1337,21 +1337,21 @@ recursively_search_psymtabs
     }
 
   partial_symbol **gbound
-    = &objfile->global_psymbols[ps->globals_offset + ps->n_global_syms];
+    = objfile->global_psymbols.data() + ps->globals_offset + ps->n_global_syms;
   partial_symbol **sbound
-    = &objfile->static_psymbols[ps->statics_offset + ps->n_static_syms];
+    = objfile->static_psymbols.data() + ps->statics_offset + ps->n_static_syms;
   partial_symbol **bound = gbound;
 
   /* Go through all of the symbols stored in a partial
      symtab in one loop.  */
-  partial_symbol **psym = &objfile->global_psymbols[ps->globals_offset];
+  partial_symbol **psym = objfile->global_psymbols.data() + ps->globals_offset;
   while (keep_going)
     {
       if (psym >= bound)
 	{
 	  if (bound == gbound && ps->n_static_syms != 0)
 	    {
-	      psym = &objfile->static_psymbols[ps->statics_offset];
+	      psym = objfile->static_psymbols.data() + ps->statics_offset;
 	      bound = sbound;
 	    }
 	  else
-- 
1.7.10.2

Re: [PATCH] Avoid indexing std::vector past the end

[Simon Marchi]

On 2017-12-30 14:31, Ruslan Kabatsayev wrote:
> The code here wants to find address of an element, and often this
> element is one past the end of std::vector. Dereferencing that element
> leads to undefined behavior, so it's better to simply use pointer
> arithmetic instead of taking address of invalid dereference.
> 
> gdb/ChangeLog:
> 
> 	* psymtab.c (recursively_search_psymtabs): Use pointer arithmetic
> 	instead of dereferencing std::vector past the end.

Hi Ruslan,

The patch LGTM, with a nit I missed the first time.  Please push with 
that fixed.

> ---
>  gdb/psymtab.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/gdb/psymtab.c b/gdb/psymtab.c
> index c87ef25..c622f4c 100644
> --- a/gdb/psymtab.c
> +++ b/gdb/psymtab.c
> @@ -1337,21 +1337,21 @@ recursively_search_psymtabs
>      }
> 
>    partial_symbol **gbound
> -    = &objfile->global_psymbols[ps->globals_offset + 
> ps->n_global_syms];
> +    = objfile->global_psymbols.data() + ps->globals_offset + 
> ps->n_global_syms;

Space before parentheses, here and in the other lines.

Thanks,

Simon