| Message ID | 20200507185016.GA13883@embeddedor (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | dmaengine: qcom: bam_dma: Replace zero-length array with flexible-array | expand |
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 <gustavoars@kernel.org> > --- > 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?
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 <jhugo@codeaurora.org>
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 <jhugo@codeaurora.org> > Awesome. :) Thanks -- Gustavo
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[]; }; /**
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/dma/qcom/bam_dma.c | 2 +- drivers/firmware/qcom_scm-legacy.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)