stm class: Replace zero-length array with flexible-array member
Subsystems (3)
PATCH 1/1 stm class: Replace zero-length array with flexible-array member
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]
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")
--- drivers/hwtracing/stm/policy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/hwtracing/stm/policy.c +1 -1
@@ -34,7 +34,7 @@ struct stp_policy_node {unsigned int first_channel;unsigned int last_channel;/* this is the one that's exposed to the attributes */ -unsigned char priv[0 ]; +unsigned char priv[]; };void *stp_policy_node_priv (struct stp_policy_node *pn)
Signature · 1 line
2.23.0
Hi all,
Friendly ping: Who can take this?
Thanks
--
Gustavo
Quoted 39 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]
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>--- drivers/hwtracing/stm/policy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)drivers/hwtracing/stm/policy.c +0
-0
drivers/hwtracing/stm/policy.c struct stp_policy_node { · line 40
Quoted 8 lines
drivers/hwtracing/stm/policy.c +1
-1@@ -34,7 +34,7 @@ struct stp_policy_node {unsigned int first_channel;unsigned int last_channel;/* this is the one that's exposed to the attributes */ -unsigned char priv[0 ]; +unsigned char priv[]; };void *stp_policy_node_priv (struct stp_policy_node *pn)
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