> On Aug 26, 2022, at 4:49 AM, Richard Biener <rguent...@suse.de> wrote:
>
> On Wed, 17 Aug 2022, Qing Zhao wrote:
>
>> Use array_at_struct_end_p to determine whether the trailing array
>> of a structure is flexible array member in __builtin_object_size.
>
> With the discussion about what array_at_struct_end_p actually computes,
> is this now the correct utility for __builtin_object_size or should
> it use a stricter variant?
My understanding is, -fstrict-flex-arrays should control all the GCC analysis
consistently, including __bultin_object_size.
For a standard conforming application, use -fstrict-flex-arrays=3 for the most
efficient code.
Kees, is it okay for Linux Kernel to add -fstrict-flex-arrays in order to
enable FORTIFY_SOURCE work better for regular trailing arrays?
Thanks.
Qing
>
>> gcc/ChangeLog:
>>
>> PR tree-optimization/101836
>> * tree-object-size.cc (addr_object_size): Use array_at_struct_end_p
>> to determine a flexible array member reference.
>>
>> gcc/testsuite/ChangeLog:
>>
>> PR tree-optimization/101836
>> * gcc.dg/pr101836.c: New test.
>> * gcc.dg/pr101836_1.c: New test.
>> * gcc.dg/pr101836_2.c: New test.
>> * gcc.dg/pr101836_3.c: New test.
>> * gcc.dg/pr101836_4.c: New test.
>> * gcc.dg/pr101836_5.c: New test.
>> * gcc.dg/strict-flex-array-5.c: New test.
>> * gcc.dg/strict-flex-array-6.c: New test.
>> ---
>> gcc/testsuite/gcc.dg/pr101836.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/pr101836_1.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/pr101836_2.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/pr101836_3.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/pr101836_4.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/pr101836_5.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/strict-flex-array-5.c | 60 ++++++++++++++++++++++
>> gcc/testsuite/gcc.dg/strict-flex-array-6.c | 60 ++++++++++++++++++++++
>> gcc/tree-object-size.cc | 16 +++---
>> 9 files changed, 487 insertions(+), 9 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836.c
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836_1.c
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836_2.c
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836_3.c
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836_4.c
>> create mode 100644 gcc/testsuite/gcc.dg/pr101836_5.c
>> create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-5.c
>> create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-6.c
>>
>> diff --git a/gcc/testsuite/gcc.dg/pr101836.c
>> b/gcc/testsuite/gcc.dg/pr101836.c
>> new file mode 100644
>> index 000000000000..efad02cfe899
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836.c
>> @@ -0,0 +1,60 @@
>> +/* -fstrict-flex-arrays is aliased with -ftrict-flex-arrays=3, which is the
>> + strictest, only [] is treated as flexible array. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), 16);
>> + expect(__builtin_object_size(trailing_1->c, 1), 4);
>> + expect(__builtin_object_size(trailing_0->c, 1), 0);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/pr101836_1.c
>> b/gcc/testsuite/gcc.dg/pr101836_1.c
>> new file mode 100644
>> index 000000000000..e2931ce1012e
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836_1.c
>> @@ -0,0 +1,60 @@
>> +/* -fstrict-flex-arrays=3 is the strictest, only [] is treated as
>> + flexible array. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=3" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), 16);
>> + expect(__builtin_object_size(trailing_1->c, 1), 4);
>> + expect(__builtin_object_size(trailing_0->c, 1), 0);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/pr101836_2.c
>> b/gcc/testsuite/gcc.dg/pr101836_2.c
>> new file mode 100644
>> index 000000000000..78974187721f
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836_2.c
>> @@ -0,0 +1,60 @@
>> +/* When -fstrict-flex-arrays=2, only [] and [0] are treated as flexiable
>> + arrays. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=2" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), 16);
>> + expect(__builtin_object_size(trailing_1->c, 1), 4);
>> + expect(__builtin_object_size(trailing_0->c, 1), -1);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/pr101836_3.c
>> b/gcc/testsuite/gcc.dg/pr101836_3.c
>> new file mode 100644
>> index 000000000000..0e69388e81fb
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836_3.c
>> @@ -0,0 +1,60 @@
>> +/* When -fstrict-flex-arrays=1, [], [0], and [1] are treated as flexible
>> + arrays. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=1" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), 16);
>> + expect(__builtin_object_size(trailing_1->c, 1), -1);
>> + expect(__builtin_object_size(trailing_0->c, 1), -1);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/pr101836_4.c
>> b/gcc/testsuite/gcc.dg/pr101836_4.c
>> new file mode 100644
>> index 000000000000..e0025aa9a7b5
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836_4.c
>> @@ -0,0 +1,60 @@
>> +/* when -fstrict-flex-arrays=0, all trailing arrays are treated as
>> + flexible arrays. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=0" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), -1);
>> + expect(__builtin_object_size(trailing_1->c, 1), -1);
>> + expect(__builtin_object_size(trailing_0->c, 1), -1);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/pr101836_5.c
>> b/gcc/testsuite/gcc.dg/pr101836_5.c
>> new file mode 100644
>> index 000000000000..0ad8bbf693ce
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr101836_5.c
>> @@ -0,0 +1,60 @@
>> +/* -fno-strict-flex-arrays is aliased to -fstrict-flex-arrays=0,
>> + all trailing arrays are treated as flexible array. */
>> +/* PR tree-optimization/101836 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fno-strict-flex-arrays" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4];
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1];
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0];
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), -1);
>> + expect(__builtin_object_size(trailing_1->c, 1), -1);
>> + expect(__builtin_object_size(trailing_0->c, 1), -1);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-5.c
>> b/gcc/testsuite/gcc.dg/strict-flex-array-5.c
>> new file mode 100644
>> index 000000000000..e474b9ec43fa
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-5.c
>> @@ -0,0 +1,60 @@
>> +/* test the combination of attribute strict_flex_arrays and option
>> + -fstrict-flex-arrays: when both attribute and option specified,
>> + attribute will have higher priority. */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=3" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4] __attribute__ ((strict_flex_arrays (0)));
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1] __attribute__ ((strict_flex_arrays (1)));
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0] __attribute__ ((strict_flex_arrays (2)));
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), -1);
>> + expect(__builtin_object_size(trailing_1->c, 1), -1);
>> + expect(__builtin_object_size(trailing_0->c, 1), -1);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-6.c
>> b/gcc/testsuite/gcc.dg/strict-flex-array-6.c
>> new file mode 100644
>> index 000000000000..b45e7b32f6d1
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-6.c
>> @@ -0,0 +1,60 @@
>> +/* test the combination of attribute strict_flex_arrays and option
>> + -fstrict-flex-arrays: when both attribute and option specified,
>> + attribute will have higher priority. */
>> +/* { dg-do run } */
>> +/* { dg-options "-O2 -fstrict-flex-arrays=0" } */
>> +
>> +#include <stdio.h>
>> +
>> +#define expect(p, _v) do { \
>> + size_t v = _v; \
>> + if (p == v) \
>> + printf("ok: %s == %zd\n", #p, p); \
>> + else \
>> + { \
>> + printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>> + __builtin_abort (); \
>> + } \
>> +} while (0);
>> +
>> +struct trailing_array_1 {
>> + int a;
>> + int b;
>> + int c[4] __attribute__ ((strict_flex_arrays (1)));
>> +};
>> +
>> +struct trailing_array_2 {
>> + int a;
>> + int b;
>> + int c[1] __attribute__ ((strict_flex_arrays (2)));
>> +};
>> +
>> +struct trailing_array_3 {
>> + int a;
>> + int b;
>> + int c[0] __attribute__ ((strict_flex_arrays (3)));
>> +};
>> +struct trailing_array_4 {
>> + int a;
>> + int b;
>> + int c[];
>> +};
>> +
>> +void __attribute__((__noinline__)) stuff(
>> + struct trailing_array_1 *normal,
>> + struct trailing_array_2 *trailing_1,
>> + struct trailing_array_3 *trailing_0,
>> + struct trailing_array_4 *trailing_flex)
>> +{
>> + expect(__builtin_object_size(normal->c, 1), 16);
>> + expect(__builtin_object_size(trailing_1->c, 1), 4);
>> + expect(__builtin_object_size(trailing_0->c, 1), 0);
>> + expect(__builtin_object_size(trailing_flex->c, 1), -1);
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + stuff((void *)argv[0], (void *)argv[0], (void *)argv[0], (void
>> *)argv[0]);
>> +
>> + return 0;
>> +}
>> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
>> index 4eb454a4a33b..1f04cb80fd0a 100644
>> --- a/gcc/tree-object-size.cc
>> +++ b/gcc/tree-object-size.cc
>> @@ -604,9 +604,9 @@ addr_object_size (struct object_size_info *osi,
>> const_tree ptr,
>> else if (var != pt_var && TREE_CODE (pt_var) == MEM_REF)
>> {
>> tree v = var;
>> - /* For &X->fld, compute object size only if fld isn't the last
>> - field, as struct { int i; char c[1]; } is often used instead
>> - of flexible array member. */
>> + /* For &X->fld, compute object size if fld isn't a flexible array
>> + member. */
>> + bool is_flexible_array_mem_ref = false;
>> while (v && v != pt_var)
>> switch (TREE_CODE (v))
>> {
>> @@ -633,6 +633,7 @@ addr_object_size (struct object_size_info *osi,
>> const_tree ptr,
>> v = NULL_TREE;
>> break;
>> }
>> + is_flexible_array_mem_ref = array_at_struct_end_p (v);
>> while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
>> if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>> != UNION_TYPE
>> @@ -645,12 +646,9 @@ addr_object_size (struct object_size_info *osi,
>> const_tree ptr,
>> && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>> == RECORD_TYPE)
>> {
>> - tree fld_chain = DECL_CHAIN (TREE_OPERAND (v, 1));
>> - for (; fld_chain; fld_chain = DECL_CHAIN (fld_chain))
>> - if (TREE_CODE (fld_chain) == FIELD_DECL)
>> - break;
>> -
>> - if (fld_chain)
>> + /* compute object size only if v is not a
>> + flexible array member. */
>> + if (!is_flexible_array_mem_ref)
>> {
>> v = NULL_TREE;
>> break;
>>
>
> --
> Richard Biener <rguent...@suse.de>
> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> HRB 36809 (AG Nuernberg)
