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Re: [PATCH] __builtin_object_size improvements

On Fri, Jun 05, 2009 at 01:22:25PM -0700, Richard Henderson wrote:
> Richard Guenther wrote:
>> On Fri, 5 Jun 2009, Richard Henderson wrote:
>>> Jakub Jelinek wrote:
>>>> The patch below implements both of these, with the exception that if
>>>> the field is at the end of the structure and base is INDIRECT_REF,
>>>> __bos (x, 1) behaves like __bos (x, 0), because there is tons of code out
>>>> there that uses arrays at the end of a structure instead of flexible array
>>>> members and I wouldn't like to break code like:
>>>> struct A { int i; char c[1]; };
>>>> struct A *p = malloc (sizeof (*p) + strlen ("abcde"));
>>>> strcpy (p->c, "abcde");
>>> I'd prefer that this exception only be made if that last array length is
>>> exactly 1, not any trailing array.
>> There are many other variants around - we hit this with the array
>> bound warnings.  So I think we have to treat all trailing arrays
>> the same.
> Guh.  Well, ok then.

The patch currently treats that way all last fields, guess I should limit
that to last fields with array type only.

struct A { char a[10]; char b; } *p;
shouldn't allow strcpy (&p->b, "abc");

Not sure about:
struct B { int i; struct A { char b; char a[10]; } j; } *p;
strcpy (&p->j.a[3], "abcdefghijklmnop");
(in this case there is array as last field in struct A, but struct A itself
is not in array).

struct B { int i; struct A { char b; char a[10]; } j[1]; } *p;
strcpy (&p->j[0].a[3], "abcdefghijklmnop");
In this case both last fields involved are arrays, but still if
the outer array were to be treated as "flexible", it would cross different
fields, so I'd say we should disallow this too.
strcpy ((char *) &p->j[0], "abcdefghijklmnop");
This should be probably considered valid.

Do you agree?


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