| Message ID | 20200507190544.GA15633@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Commit | 914a1951d88968371c7d43400c9d936382cd7d69 |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
| Series | PCI: Replace zero-length array with flexible-array | expand |
On Thu, May 07, 2020 at 02:05:44PM -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> Applied to pci/misc for v5.8, thanks! I assume this takes care of everything in drivers/pci/, right? I'd like to do them all at once, so if there are others, send another patch and I'll squash them. I took a quick look but didn't see any. > --- > drivers/pci/pci.c | 2 +- > include/linux/pci.h | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 595fcf59843f..bb78f580814e 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -1578,7 +1578,7 @@ 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[]; > }; > > /** > diff --git a/include/linux/pci.h b/include/linux/pci.h > index 83ce1cdf5676..0453ee458ab1 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -279,7 +279,7 @@ struct pci_cap_saved_data { > u16 cap_nr; > bool cap_extended; > unsigned int size; > - u32 data[0]; > + u32 data[]; > }; > > struct pci_cap_saved_state { > @@ -532,7 +532,7 @@ struct pci_host_bridge { > resource_size_t start, > resource_size_t size, > resource_size_t align); > - unsigned long private[0] ____cacheline_aligned; > + unsigned long private[] ____cacheline_aligned; > }; > > #define to_pci_host_bridge(n) container_of(n, struct pci_host_bridge, dev) >
On Thu, May 07, 2020 at 03:15:44PM -0500, Bjorn Helgaas wrote: > On Thu, May 07, 2020 at 02:05:44PM -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[]; > > }; > > > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> > > Applied to pci/misc for v5.8, thanks! > > I assume this takes care of everything in drivers/pci/, right? I'd > like to do them all at once, so if there are others, send another > patch and I'll squash them. I took a quick look but didn't see any. > Yep. I can confirm that these are the last zero-length arrays in drivers/pci/ :) Thanks -- Gustavo
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 595fcf59843f..bb78f580814e 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -1578,7 +1578,7 @@ 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[]; }; /** diff --git a/include/linux/pci.h b/include/linux/pci.h index 83ce1cdf5676..0453ee458ab1 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -279,7 +279,7 @@ struct pci_cap_saved_data { u16 cap_nr; bool cap_extended; unsigned int size; - u32 data[0]; + u32 data[]; }; struct pci_cap_saved_state { @@ -532,7 +532,7 @@ struct pci_host_bridge { resource_size_t start, resource_size_t size, resource_size_t align); - unsigned long private[0] ____cacheline_aligned; + unsigned long private[] ____cacheline_aligned; }; #define to_pci_host_bridge(n) container_of(n, struct pci_host_bridge, dev)
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> --- drivers/pci/pci.c | 2 +- include/linux/pci.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)