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Re: [PATCH] Handle overlength strings in the C FE
- From: Bernd Edlinger <bernd dot edlinger at hotmail dot de>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Biener <rguenther at suse dot de>, Jakub Jelinek <jakub at redhat dot com>, Jeff Law <law at redhat dot com>, Martin Sebor <msebor at gmail dot com>
- Date: Wed, 1 Aug 2018 20:06:53 +0000
- Subject: Re: [PATCH] Handle overlength strings in the C FE
- References: <AM5PR0701MB26577C800216899DCF6647E6E42F0@AM5PR0701MB2657.eurprd07.prod.outlook.com> <alpine.DEB.firstname.lastname@example.org> <AM5PR0701MB26578DF7C6DA998944B41E5BE42D0@AM5PR0701MB2657.eurprd07.prod.outlook.com> <alpine.DEB.email@example.com>
On 08/01/18 18:04, Joseph Myers wrote:
> On Wed, 1 Aug 2018, Bernd Edlinger wrote:
>> On 07/30/18 17:49, Joseph Myers wrote:
>>> On Mon, 30 Jul 2018, Bernd Edlinger wrote:
>>>> this is how I would like to handle the over length strings issue in the C FE.
>>>> If the string constant is exactly the right length and ends in one explicit
>>>> NUL character, shorten it by one character.
>>> I don't think shortening should be limited to that case. I think the case
>>> where the constant is longer than that (and so gets an unconditional
>>> pedwarn) should also have it shortened - any constant that doesn't fit in
>>> the object being initialized should be shortened to fit, whether diagnosed
>>> or not, we should define GENERIC / GIMPLE to disallow too-large string
>>> constants in initializers, and should add an assertion somewhere in the
>>> middle-end that no too-large string constants reach it.
>> Okay, there is an update following your suggestion.
> It seems odd to me to have two separate bits of code dealing with reducing
> the length, rather than something like
> if (too long)
> /* Decide whether to do a pedwarn_init, or a warn_cxx_compat warning,
> or neither. */
> /* Shorten string, in either case. */
> The memcmp with "\0\0\0\0" is introducing a hidden assumption that any
> sort of character in strings is never more than four bytes. It also seems
> unnecessary, in that ultimately the over-long string should be shortened
> regardless of whether what's being removed is a zero character or not.
> > It should not be possible to be over-long and fail tree_fits_uhwi_p
> (TYPE_SIZE_UNIT (type)), simply because STRING_CST lengths are stored in
> host int (even if, ideally, they'd use some other type to allow for
> STRING_CSTs over 2GB in size). (And I don't think GCC can represent
> target type sizes that don't fit in unsigned HOST_WIDE_INT anyway; the
> only way for a target type size in bytes to fail to be representable in
> unsigned HOST_WIDE_INT should be if the size is not constant.)
A new simplified version of the patch is attached.
Bootstrapped and reg-tested as usual.
Is it OK for trunk?
2018-08-01 Bernd Edlinger <firstname.lastname@example.org>
* c-typeck.c (digest_init): Shorten overlength strings.
diff -pur gcc/c/c-typeck.c gcc/c/c-typeck.c
--- gcc/c/c-typeck.c 2018-06-20 18:35:15.000000000 +0200
+++ gcc/c/c-typeck.c 2018-07-31 18:49:50.757586625 +0200
@@ -7435,19 +7435,17 @@ digest_init (location_t init_loc, tree type, tree
- TREE_TYPE (inside_init) = type;
if (TYPE_DOMAIN (type) != NULL_TREE
&& TYPE_SIZE (type) != NULL_TREE
&& TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST)
unsigned HOST_WIDE_INT len = TREE_STRING_LENGTH (inside_init);
+ unsigned unit = TYPE_PRECISION (typ1) / BITS_PER_UNIT;
/* Subtract the size of a single (possibly wide) character
because it's ok to ignore the terminating null char
that is counted in the length of the constant. */
- if (compare_tree_int (TYPE_SIZE_UNIT (type),
- (len - (TYPE_PRECISION (typ1)
- / BITS_PER_UNIT))) < 0)
+ if (compare_tree_int (TYPE_SIZE_UNIT (type), len - unit) < 0)
pedwarn_init (init_loc, 0,
("initializer-string for array of chars "
"is too long"));
@@ -7456,8 +7454,21 @@ digest_init (location_t init_loc, tree type, tree
warning_at (init_loc, OPT_Wc___compat,
("initializer-string for array chars "
"is too long for C++"));
+ if (compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0)
+ unsigned HOST_WIDE_INT size
+ = tree_to_uhwi (TYPE_SIZE_UNIT (type));
+ const char *p = TREE_STRING_POINTER (inside_init);
+ char *q = (char *)xmalloc (size + unit);
+ memcpy (q, p, size);
+ memset (q + size, 0, unit);
+ inside_init = build_string (size + unit, q);
+ free (q);
+ TREE_TYPE (inside_init) = type;
else if (INTEGRAL_TYPE_P (typ1))