Re: Fix -Wstringop-overflow regression

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Apr 4, 2018 at 3:34 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> we shouldn't claim string overflows for character arrays at
> end of structures; the code that tries to avoid these
> accidentally passed the address of the accessed member to
> array_at_struct_end_p(), but that one wants the component_ref
> or array_ref itself.  Needs updating of one testcase that
> incorrectly expected warning to occur in this situation.
> (The regression is that we warn about the testcase now, where we
> didn't warn before)

Bootstrapped and tested ...?

OK.

Thanks,
Richard.

>
>         * builtins.c (compute_objsize): Pass correct operand
>         to array_at_struct_end_p.
>
> testsuite/
>         * gcc.dg/Wstringop-overflow-4.c: New test.
>         * c-c++-common/Wstringop-truncation-4.c: Adjust.
>
> diff --git a/gcc/builtins.c b/gcc/builtins.c
> index 487d9d5..3554cdb 100644
> --- a/gcc/builtins.c
> +++ b/gcc/builtins.c
> @@ -3379,7 +3379,7 @@ compute_objsize (tree dest, int ostype)
>    type = TYPE_MAIN_VARIANT (type);
>
>    if (TREE_CODE (type) == ARRAY_TYPE
> -      && !array_at_struct_end_p (dest))
> +      && !array_at_struct_end_p (TREE_OPERAND (dest, 0)))
>      {
>        /* Return the constant size unless it's zero (that's a zero-length
>          array likely at the end of a struct).  */
> diff --git a/gcc/testsuite/c-c++-common/Wstringop-truncation-4.c b/gcc/testsuite/c-c++-common/Wstringop-truncation-4.c
> index c4ad4d6..c76f282 100644
> --- a/gcc/testsuite/c-c++-common/Wstringop-truncation-4.c
> +++ b/gcc/testsuite/c-c++-common/Wstringop-truncation-4.c
> @@ -23,7 +23,7 @@ void test_arrays (struct Arrays *p, const char *s)
>  {
>    strncpy (p->a, s, sizeof p->a);           /* { dg-warning "\\\[-Wstringop-truncation" } */
>    strncpy ((char*)p->b, s, sizeof p->b);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> -  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> +  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
>  }
>
>  struct Pointers
> @@ -51,7 +51,7 @@ void test_const_arrays (struct ConstArrays *p, const char *s)
>  {
>    strncpy ((char*)p->a, s, sizeof p->a);    /* { dg-warning "\\\[-Wstringop-truncation" } */
>    strncpy ((char*)p->b, s, sizeof p->b);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> -  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> +  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
>  }
>
>  struct ConstPointers
> @@ -79,7 +79,7 @@ void test_volatile_arrays (struct VolatileArrays *p, const char *s)
>  {
>    strncpy ((char*)p->a, s, sizeof p->a);    /* { dg-warning "\\\[-Wstringop-truncation" } */
>    strncpy ((char*)p->b, s, sizeof p->b);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> -  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> +  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
>  }
>
>  struct VolatilePointers
> @@ -107,7 +107,7 @@ void test_const_volatile_arrays (struct ConstVolatileArrays *p, const char *s)
>  {
>    strncpy ((char*)p->a, s, sizeof p->a);    /* { dg-warning "\\\[-Wstringop-truncation" } */
>    strncpy ((char*)p->b, s, sizeof p->b);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> -  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-warning "\\\[-Wstringop-truncation" } */
> +  strncpy ((char*)p->c, s, sizeof p->c);    /* { dg-bogus "\\\[-Wstringop-truncation" } */
>  }
>
>  struct ConstVolatilePointers
> diff --git a/gcc/testsuite/gcc.dg/Wstringop-overflow-4.c b/gcc/testsuite/gcc.dg/Wstringop-overflow-4.c
> new file mode 100644
> index 0000000..5905b26
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/Wstringop-overflow-4.c
> @@ -0,0 +1,28 @@
> +/* { dg-do compile }
> +   { dg-options "-O2 -Wstringop-overflow" } */
> +
> +extern char* strchr (const char*, int);
> +extern char* strcpy (char*, const char*);
> +extern void* malloc (__SIZE_TYPE__);
> +extern __SIZE_TYPE__ strlen (const char *);
> +struct define_item {
> +    int len;
> +    char value[1];
> +};
> +
> +struct define_item * foo(char *name)
> +{
> +  char * p;
> +  char * value;
> +  struct define_item * ptr;
> +
> +  p = strchr (name, '=');
> +  if (1 && p) {
> +      value = p+1;
> +  } else
> +    value = "1";
> +
> +  ptr = malloc(sizeof(struct define_item) + strlen(value));
> +  strcpy(ptr->value, value);  /* { dg-bogus "bytes into a region" } */
> +  return ptr;
> +}