| Message ID | 20200507190052.GA15325@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | c4ad6ea9574bfa29ca00ddf6b6b1508ec344ff45 |
| Headers | show |
| Series | MIPS: Replace zero-length array with flexible-array | expand |
On Thu, May 07, 2020 at 02:00:52PM -0500, Gustavo A. R. Silva wrote: > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to declare > variable-length types such as these ones is a flexible array member[1][2], > introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. > > Also, notice that, dynamic memory allocations won't be affected by > this change: > > "Flexible array members have incomplete type, and so the sizeof operator > may not be applied. As a quirk of the original implementation of > zero-length arrays, sizeof evaluates to zero."[1] > > sizeof(flexible-array-member) triggers a warning because flexible array > members have incomplete type[1]. There are some instances of code in > which the sizeof operator is being incorrectly/erroneously applied to > zero-length arrays and the result is zero. Such instances may be hiding > some bugs. So, this work (flexible-array member conversions) will also > help to get completely rid of those sorts of issues. > > This issue was found with the help of Coccinelle. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> > --- > arch/mips/kernel/signal.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) applied to mips-next. Thomas.
On Fri, May 08, 2020 at 03:02:49PM +0200, Thomas Bogendoerfer wrote: > > > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> > > --- > > arch/mips/kernel/signal.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > applied to mips-next. > Thanks, Thomas. -- Gustavo
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c index f6efabcb4e92..4ee626049d92 100644 --- a/arch/mips/kernel/signal.c +++ b/arch/mips/kernel/signal.c @@ -52,7 +52,7 @@ struct sigframe { /* Matches struct ucontext from its uc_mcontext field onwards */ struct sigcontext sf_sc; sigset_t sf_mask; - unsigned long long sf_extcontext[0]; + unsigned long long sf_extcontext[]; }; struct rt_sigframe {
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> --- arch/mips/kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)