* [PATCH] PCI: Replace zero-length array with flexible-array member
@ 2020-02-13 0:52 Gustavo A. R. Silva
2020-03-05 11:29 ` Lorenzo Pieralisi
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-13 0:52 UTC (permalink / raw)
To: Bjorn Helgaas; +Cc: linux-pci, linux-kernel, 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] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
drivers/pci/pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d828ca835a98..3217b8cdb1e0 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1521,7 +1521,7 @@ EXPORT_SYMBOL(pci_restore_state);
struct pci_saved_state {
u32 config_space[16];
- struct pci_cap_saved_data cap[0];
+ struct pci_cap_saved_data cap[];
};
/**
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] PCI: Replace zero-length array with flexible-array member
2020-02-13 0:52 [PATCH] PCI: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-05 11:29 ` Lorenzo Pieralisi
0 siblings, 0 replies; 2+ messages in thread
From: Lorenzo Pieralisi @ 2020-03-05 11:29 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: Bjorn Helgaas, linux-pci, linux-kernel
On Wed, Feb 12, 2020 at 06:52:21PM -0600, 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]
>
> 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 <gustavo@embeddedor.com>
> ---
> drivers/pci/pci.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Applied to pci/hv for v5.7, thanks.
Lorenzo
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index d828ca835a98..3217b8cdb1e0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1521,7 +1521,7 @@ EXPORT_SYMBOL(pci_restore_state);
>
> struct pci_saved_state {
> u32 config_space[16];
> - struct pci_cap_saved_data cap[0];
> + struct pci_cap_saved_data cap[];
> };
>
> /**
> --
> 2.23.0
>
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