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 <[email protected]>
---
drivers/dma/qcom/bam_dma.c | 2 +-
drivers/firmware/qcom_scm-legacy.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index ef73f65224b1..5a08dd0d3388 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -74,7 +74,7 @@ struct bam_async_desc {
struct list_head desc_node;
enum dma_transfer_direction dir;
size_t length;
- struct bam_desc_hw desc[0];
+ struct bam_desc_hw desc[];
};
enum bam_reg {
diff --git a/drivers/firmware/qcom_scm-legacy.c b/drivers/firmware/qcom_scm-legacy.c
index 8532e7c78ef7..eba6b60bfb61 100644
--- a/drivers/firmware/qcom_scm-legacy.c
+++ b/drivers/firmware/qcom_scm-legacy.c
@@ -56,7 +56,7 @@ struct scm_legacy_command {
__le32 buf_offset;
__le32 resp_hdr_offset;
__le32 id;
- __le32 buf[0];
+ __le32 buf[];
};
/**
On 5/7/2020 12:50 PM, 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 <[email protected]>
> ---
> drivers/dma/qcom/bam_dma.c | 2 +-
> drivers/firmware/qcom_scm-legacy.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
Shouldn't these two files be two different patches?
--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
On Thu, May 07, 2020 at 01:24:57PM -0600, Jeffrey Hugo wrote:
> > drivers/dma/qcom/bam_dma.c | 2 +-
> > drivers/firmware/qcom_scm-legacy.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
>
> Shouldn't these two files be two different patches?
>
I believe so... I'll split this patch up into two patches.
Thanks
--
Gustavo
On 5/8/2020 11:02 AM, Gustavo A. R. Silva wrote:
> On Thu, May 07, 2020 at 01:24:57PM -0600, Jeffrey Hugo wrote:
>>> drivers/dma/qcom/bam_dma.c | 2 +-
>>> drivers/firmware/qcom_scm-legacy.c | 2 +-
>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>
>> Shouldn't these two files be two different patches?
>>
>
> I believe so... I'll split this patch up into two patches.
>
> Thanks
> --
> Gustavo
>
Sounds good to me. When you do, you can add the following if you like
Reviewed-by: Jeffrey Hugo <[email protected]>
--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
On Fri, May 08, 2020 at 11:20:16AM -0600, Jeffrey Hugo wrote:
> On 5/8/2020 11:02 AM, Gustavo A. R. Silva wrote:
> > On Thu, May 07, 2020 at 01:24:57PM -0600, Jeffrey Hugo wrote:
> > > > drivers/dma/qcom/bam_dma.c | 2 +-
> > > > drivers/firmware/qcom_scm-legacy.c | 2 +-
> > > > 2 files changed, 2 insertions(+), 2 deletions(-)
> > > >
> > >
> > > Shouldn't these two files be two different patches?
> > >
> >
> > I believe so... I'll split this patch up into two patches.
> >
> > Thanks
> > --
> > Gustavo
> >
>
> Sounds good to me. When you do, you can add the following if you like
>
> Reviewed-by: Jeffrey Hugo <[email protected]>
>
Awesome. :)
Thanks
--
Gustavo