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* [Bug c/53548] New: allow flexible array members in unions like zero-length arrays
@ 2012-06-01 2:13 vapier at gentoo dot org
2012-06-04 0:50 ` [Bug c/53548] " carlos_odonell at mentor dot com
` (10 more replies)
0 siblings, 11 replies; 12+ messages in thread
From: vapier at gentoo dot org @ 2012-06-01 2:13 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
Bug #: 53548
Summary: allow flexible array members in unions like
zero-length arrays
Classification: Unclassified
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: vapier@gentoo.org
gcc will accept this code:
struct {
short op;
union {
int i;
char foo[0];
};
};
but rejects this:
struct {
short op;
union {
int i;
char foo[];
};
};
with the error:
error: flexible array member in otherwise empty struct
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
@ 2012-06-04 0:50 ` carlos_odonell at mentor dot com
2024-03-08 20:41 ` kees at outflux dot net
` (9 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: carlos_odonell at mentor dot com @ 2012-06-04 0:50 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
Carlos O'Donell <carlos_odonell at mentor dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |carlos_odonell at mentor
| |dot com
--- Comment #1 from Carlos O'Donell <carlos_odonell at mentor dot com> 2012-06-04 00:49:55 UTC ---
There are several practical cases where it would be nice to support this kind
of construct. Structures that *end* with a variable length arrays are used in
networking to represent a variable length result. In particular the example in
this issue is taken from a recent reworking of tftp.h in glibc which uses a
similar construct.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
2012-06-04 0:50 ` [Bug c/53548] " carlos_odonell at mentor dot com
@ 2024-03-08 20:41 ` kees at outflux dot net
2024-03-08 20:42 ` kees at outflux dot net
` (8 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: kees at outflux dot net @ 2024-03-08 20:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
Kees Cook <kees at outflux dot net> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |carlos at gcc dot gnu.org,
| |kees at outflux dot net,
| |ndesaulniers at google dot com,
| |qing.zhao at oracle dot com
--- Comment #6 from Kees Cook <kees at outflux dot net> ---
There is still no way to use C99 flexible arrays in unions (or alone in
structs) without syntactic obfuscation. The extension that already allows
0-sized arrays in unions should be extended to cover C99 arrays. This is
especially important for projects migrating away from the various deprecated
"fake" flexible array members to C99 flex array members, as they continue to
depend on both union membership and single-member structs (i.e. the Linux
kernel has lots of these, some even in UAPI).
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
2012-06-04 0:50 ` [Bug c/53548] " carlos_odonell at mentor dot com
2024-03-08 20:41 ` kees at outflux dot net
@ 2024-03-08 20:42 ` kees at outflux dot net
2024-03-08 20:50 ` kees at outflux dot net
` (7 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: kees at outflux dot net @ 2024-03-08 20:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #7 from Kees Cook <kees at outflux dot net> ---
There is still no way to use C99 flexible arrays in unions (or alone in
structs) without syntactic obfuscation. The extension that already allows
0-sized arrays in unions should be extended to cover C99 arrays. This is
especially important for projects migrating away from the various deprecated
"fake" flexible array members to C99 flex array members, as they continue to
depend on both union membership and single-member structs (i.e. the Linux
kernel has lots of these, some even in UAPI).
Please reopen this bug. :) Clang is also preparing to fix this issue.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (2 preceding siblings ...)
2024-03-08 20:42 ` kees at outflux dot net
@ 2024-03-08 20:50 ` kees at outflux dot net
2024-03-13 19:34 ` qinzhao at gcc dot gnu.org
` (6 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: kees at outflux dot net @ 2024-03-08 20:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #8 from Kees Cook <kees at outflux dot net> ---
Clang bug: https://github.com/llvm/llvm-project/issues/84565
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (3 preceding siblings ...)
2024-03-08 20:50 ` kees at outflux dot net
@ 2024-03-13 19:34 ` qinzhao at gcc dot gnu.org
2024-04-08 18:20 ` qinzhao at gcc dot gnu.org
` (5 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: qinzhao at gcc dot gnu.org @ 2024-03-13 19:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
qinzhao at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |qinzhao at gcc dot gnu.org
Status|RESOLVED |REOPENED
Resolution|WONTFIX |---
--- Comment #9 from qinzhao at gcc dot gnu.org ---
I think that we need to add this support as an GCC extension
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (4 preceding siblings ...)
2024-03-13 19:34 ` qinzhao at gcc dot gnu.org
@ 2024-04-08 18:20 ` qinzhao at gcc dot gnu.org
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: qinzhao at gcc dot gnu.org @ 2024-04-08 18:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #10 from qinzhao at gcc dot gnu.org ---
Clang has accept this extension:
https://github.com/llvm/llvm-project/pull/84428
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (5 preceding siblings ...)
2024-04-08 18:20 ` qinzhao at gcc dot gnu.org
@ 2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-05-06 18:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Qing Zhao <qinzhao@gcc.gnu.org>:
https://gcc.gnu.org/g:adb1c8a0f167c3a1f7593d75f5a10eb07a5d741a
commit r15-208-gadb1c8a0f167c3a1f7593d75f5a10eb07a5d741a
Author: Qing Zhao <qing.zhao@oracle.com>
Date: Mon May 6 16:25:04 2024 +0000
Allow flexible array members in unions and alone in structures [PR53548]
The request for GCC to accept that the C99 flexible array member can be
in a union or alone in a structure has been made a long time ago around
2012
for supporting several practical cases including glibc.
A GCC PR has been opened for such request at that time:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
However, this PR was closed as WONTFIX around 2015 due to the following
reason:
"there is an existing extension that makes the requested functionality
possible"
i.e GCC fully supported that the zero-length array can be in a union or
alone
in a structure for a long time. (though I didn't see any official
documentation
on such extension)
It's reasonable to close PR53548 at that time since zero-length array
extension
can be used for such purpose.
However, since GCC13, in order to improve the C/C++ security, we introduced
-fstrict-flex-arrays=n to gradually eliminate the "fake flexible array"
usages from C/C++ source code. As a result, zero-length arrays eventually
will be replaced by C99 flexiable array member completely.
Therefore, GCC needs to explicitly allow such extensions directly for C99
flexible arrays, since flexable array member in unions or alone in structs
are common code patterns in active use by the Linux kernel (and other
projects).
For example, these do not error by default with GCC:
union one {
int a;
int b[0];
};
union two {
int a;
struct {
struct { } __empty;
int b[];
};
};
But these do:
union three {
int a;
int b[];
};
struct four {
int b[];
}
Clang has supported such extensions since March, 2024
https://github.com/llvm/llvm-project/pull/84428
GCC should also support such extensions. This will allow for
a seamless transition for code bases away from zero-length arrays without
losing existing code patterns.
gcc/ChangeLog:
PR c/53548
* doc/extend.texi: Add documentation for Flexible Array Members in
Unions and Flexible Array Members alone in Structures.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (6 preceding siblings ...)
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
@ 2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
10 siblings, 0 replies; 12+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-05-06 18:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #12 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Qing Zhao <qinzhao@gcc.gnu.org>:
https://gcc.gnu.org/g:f27fc59d9f7c735d200fda647a487850144b10eb
commit r15-209-gf27fc59d9f7c735d200fda647a487850144b10eb
Author: Qing Zhao <qing.zhao@oracle.com>
Date: Mon May 6 16:26:19 2024 +0000
C and C++ FE changes to support flexible array members in unions and alone
in structures. Adjust testcases for flexible array member in union and alone in
structure extension.
PR c/53548
gcc/c/ChangeLog:
PR c/53548
* c-decl.cc (finish_struct): Change errors to pedwarns for the
cases
flexible array members in union or alone in structures.
gcc/cp/ChangeLog:
PR c/53548
* class.cc (diagnose_flexarrays): Change error to pdewarn for the
case
flexible array members alone in structures.
* decl.cc (grokdeclarator): Change error to pdewarn for the case
flexible array members in unions.
gcc/ChangeLog:
PR c/53548
* stor-layout.cc (place_union_field): Use zero sizes for flexible
array
member fields.
gcc/testsuite/ChangeLog:
PR c/53548
* c-c++-common/builtin-clear-padding-3.c: Adjust testcase.
* g++.dg/ext/flexary12.C: Likewise.
* g++.dg/ext/flexary19.C: Likewise.
* g++.dg/ext/flexary2.C: Likewise.
* g++.dg/ext/flexary3.C: Likewise.
* g++.dg/ext/flexary36.C: Likewise.
* g++.dg/ext/flexary4.C: Likewise.
* g++.dg/ext/flexary5.C: Likewise.
* g++.dg/ext/flexary8.C: Likewise.
* g++.dg/torture/pr64280.C: Likewise.
* gcc.dg/20050620-1.c: Likewise.
* gcc.dg/940510-1.c: Likewise.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (7 preceding siblings ...)
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
@ 2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
2024-05-06 18:40 ` qinzhao at gcc dot gnu.org
10 siblings, 0 replies; 12+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-05-06 18:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Qing Zhao <qinzhao@gcc.gnu.org>:
https://gcc.gnu.org/g:93f6a47583f3fa8a1b66856ecb19ec28f26b2ba4
commit r15-210-g93f6a47583f3fa8a1b66856ecb19ec28f26b2ba4
Author: Qing Zhao <qing.zhao@oracle.com>
Date: Mon May 6 16:27:09 2024 +0000
Add testing cases for flexible array members in unions and alone in
structures.
PR c/53548
gcc/testsuite/ChangeLog:
PR c/53548
* c-c++-common/fam-in-union-alone-in-struct-1.c: New testcase.
* c-c++-common/fam-in-union-alone-in-struct-2.c: New testcase.
* c-c++-common/fam-in-union-alone-in-struct-3.c: New testcase.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (8 preceding siblings ...)
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
@ 2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
2024-05-06 18:40 ` qinzhao at gcc dot gnu.org
10 siblings, 0 replies; 12+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-05-06 18:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
--- Comment #14 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Qing Zhao <qinzhao@gcc.gnu.org>:
https://gcc.gnu.org/g:6634a409124a884ff66b3756568a7daae7d3c295
commit r15-211-g6634a409124a884ff66b3756568a7daae7d3c295
Author: Qing Zhao <qing.zhao@oracle.com>
Date: Mon May 6 16:28:01 2024 +0000
Update the C FE routine "add_flexible_array_elts_to_size" C++ FE routine
"layout_var_decl" to handle the cases when the DECL is union.
PR c/53548
Add testing cases to test the _bos for flexible array members in unions
or alone in structures.
gcc/c/ChangeLog:
PR c/53548
* c-decl.cc (add_flexible_array_elts_to_size): Handle the cases
when the DECL is union.
gcc/cp/ChangeLog:
PR c/53548
* decl.cc (layout_var_decl): Handle the cases when the DECL is
union with a flexible array member initializer.
gcc/testsuite/ChangeLog:
PR c/53548
* c-c++-common/fam-in-union-alone-in-struct-bos-1.c: New test.
* c-c++-common/fam-in-union-alone-in-struct-bos.c: New test.
^ permalink raw reply [flat|nested] 12+ messages in thread
* [Bug c/53548] allow flexible array members in unions like zero-length arrays
2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
` (9 preceding siblings ...)
2024-05-06 18:36 ` cvs-commit at gcc dot gnu.org
@ 2024-05-06 18:40 ` qinzhao at gcc dot gnu.org
10 siblings, 0 replies; 12+ messages in thread
From: qinzhao at gcc dot gnu.org @ 2024-05-06 18:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53548
qinzhao at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Version|unknown |15.0
Status|REOPENED |RESOLVED
Resolution|--- |FIXED
--- Comment #15 from qinzhao at gcc dot gnu.org ---
Fixed in GCC15
^ permalink raw reply [flat|nested] 12+ messages in thread
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2012-06-01 2:13 [Bug c/53548] New: allow flexible array members in unions like zero-length arrays vapier at gentoo dot org
2012-06-04 0:50 ` [Bug c/53548] " carlos_odonell at mentor dot com
2024-03-08 20:41 ` kees at outflux dot net
2024-03-08 20:42 ` kees at outflux dot net
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2024-03-13 19:34 ` qinzhao at gcc dot gnu.org
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