MIPS: Replace zero-length array with flexible-array
PATCH 1/1 MIPS: Replace zero-length array with flexible-array
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")
--- arch/mips/kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
arch/mips/kernel/signal.c +1 -1
@@ -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 {
Quoted 31 lines · Gustavo A. R. Silva
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.
Quoted 8 lines
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>--- arch/mips/kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
applied to mips-next.
Thomas.
Signature · 2 lines
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]
Quoted 8 lines · Thomas Bogendoerfer
Quoted 5 lines
Signed-off-by Gustavo A. R. Silva <[email protected]>--- arch/mips/kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)applied to mips-next.
Thanks, Thomas.
--
Gustavo