On 08/22/18 18:28, Martin Sebor wrote:
> On 08/22/2018 08:41 AM, Bernd Edlinger wrote:
>> Hi!
>>
>>
>> This patch adds some more checks to c_getstr to fix PR middle-end/87053
>> wrong code bug.
>>
>> Unfortunately this patch alone is not sufficient to fix the problem,
>> but also the patch for PR 86714 that hardens c_getstr is necessary
>> to prevent the wrong folding.
>>
>>
>> Bootstrapped and reg-tested on top of my PR 86711/86714 patch.
>> Is it OK for trunk?
>
> This case is also the subject of the patch I submitted back in
> July for 86711/86714 and 86552. With it, GCC avoid folding
> the strlen call early and warns for the missing nul:
>
> warning: ‘__builtin_strlen’ argument missing terminating nul
> [-Wstringop-overflow=]
> if (__builtin_strlen (u.z) != 7)
> ^~~~~~~~~~~~~~~~
>
> The patch doesn't doesn't prevent all such strings from being
> folded and it eventually lets fold_builtin_strlen() do its thing:
>
> /* To avoid warning multiple times about unterminated
> arrays only warn if its length has been determined
> and is being folded to a constant. */
> if (nonstr)
> warn_string_no_nul (loc, NULL_TREE, fndecl, nonstr);
>
> return fold_convert_loc (loc, type, len);
>
> Handling this case is a matter of avoiding the folding here as
> well and moving the warning later.
>
> Since my patch is still in the review queue and does much more
> than just prevent folding of non-nul terminated arrays it should
> be reviewed first.
>
Hmmm, now you made me curious.
So I tried to install your patch (I did this on r263508
since it does not apply to trunk, one thing I noted is
that part 4 and part 3 seem to create gcc/testsuite/gcc.dg/warn-strcpy-no-nul.c
I did not check if they are identical or not).
So I tried the test case from this PR on the compiler built with your patch:
$ cat cat pr87053.c
/* PR middle-end/87053 */
const union
{ struct {
char x[4];
char y[4];
};
struct {
char z[8];
};
} u = {{"1234", "567"}};
int main ()
{
if (__builtin_strlen (u.z) != 7)
__builtin_abort ();
}
$ gcc -S pr87053.c
pr87053.c: In function 'main':
pr87053.c:15:7: warning: '__builtin_strlen' argument missing terminating nul
[-Wstringop-overflow=]
15 | if (__builtin_strlen (u.z) != 7)
| ^~~~~~~~~~~~~~~~
pr87053.c:11:3: note: referenced argument declared here
11 | } u = {{"1234", "567"}};
| ^
$ cat pr87053.s
.file "pr87053.c"
.text
.globl u
.section .rodata
.align 8
.type u, @object
.size u, 8
u:
.ascii "1234"
.string "567"
.text
.globl main
.type main, @function
main:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
call abort
.cfi_endproc
.LFE0:
.size main, .-main
.ident "GCC: (GNU) 9.0.0 20180813 (experimental)"
.section .note.GNU-stack,"",@progbits
So we get a warning, and still wrong code.
That is the reason why I think this patch of yours adds
confusion by trying to fix everything in one step.
And I would like you to think of ways how to solve
a problem step by step.
And at this time, sorry, we should restore correctness issues.
And fix wrong-code issues.
If possible without breaking existing warnings, yes.
But no new warnings, sorry again.
Bernd.
