7f93ae8086
The -fstrict-flex-arrays=3 is the most restrictive type of flex arrays.
No number, including 0, is allowed in the FAM. In the cases where a "0"
is used, the resulting size is the same as if a zero-sized object were
substituted.
This is needed for proper _FORTIFY_SOURCE coverage in the Linux kernel,
among other reasons. So while the only reason for specifying a
zero-length array at the end of a structure is for specify a FAM,
treating it as such will cause _FORTIFY_SOURCE not to work correctly;
__builtin_object_size will report -1 instead of 0 for a destination
buffer size to keep any kernel internals from using the deprecated
members as fake FAMs.
For example:
struct broken {
int foo;
int fake_fam[0];
struct something oops;
};
There have been bugs where the above struct was created because "oops"
was added after "fake_fam" by someone not realizing. Under
__FORTIFY_SOURCE, doing:
memcpy(p->fake_fam, src, len);
raises no warnings when __builtin_object_size(p->fake_fam, 1) returns -1
and may stomp on "oops."
Omitting a warning when using the (invalid) zero-length array is how GCC
treats -fstrict-flex-arrays=3. A warning in that situation is likely an
irritant, because requesting this option level is explicitly requesting
this behavior.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836
Differential Revision: https://reviews.llvm.org/D134902
41 lines
1.3 KiB
C++
41 lines
1.3 KiB
C++
// RUN: %clang_cc1 -verify=relaxed -fstrict-flex-arrays=1 %s
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// RUN: %clang_cc1 -verify=relaxed,strict -fstrict-flex-arrays=2 %s
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// RUN: %clang_cc1 -verify=relaxed,strict,very-strict -fstrict-flex-arrays=3 %s
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// We cannot know for sure the size of a flexible array.
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struct t {
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int f;
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int a[];
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};
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void test(t *s2) {
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s2->a[2] = 0; // no-warning
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}
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// Under -fstrict-flex-arrays={1,2,3} `a` is not a flexible array
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struct t0 {
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int f;
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int a[10]; // relaxed-note {{array 'a' declared here}}
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};
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void test0(t0 *s2) {
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s2->a[12] = 0; // relaxed-warning {{array index 12 is past the end of the array (that has type 'int[10]')}}
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}
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// Under -fstrict-flex-arrays=2 `a` is not a flexible array, but it is under -fstrict-flex-arrays=1
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struct t1 {
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int f;
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int a[1]; // strict-note {{array 'a' declared here}}
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};
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void test1(t1 *s2) {
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s2->a[2] = 0; // strict-warning {{array index 2 is past the end of the array (that has type 'int[1]')}}
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}
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// Under -fstrict-flex-arrays={1,2} `a` is a flexible array, but not under -fstrict-flex-arrays=3.
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struct t2 {
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int f;
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int a[0]; // very-strict-note {{array 'a' declared here}}
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};
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void test1(t2 *s2) {
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s2->a[2] = 0; // very-strict-warning {{array index 2 is past the end of the array (that has type 'int[0]')}}
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}
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