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SubjectRe: [PATCH 1/3] media: saa7146: avoid high stack usage with clang
On Tue, Feb 19, 2019 at 9:02 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> Two saa7146/hexium files contain a construct that causes a warning
> when built with clang:
>
> drivers/media/pci/saa7146/hexium_orion.c:210:12: error: stack frame size of 2272 bytes in function 'hexium_probe'
> [-Werror,-Wframe-larger-than=]
> static int hexium_probe(struct saa7146_dev *dev)
> ^
> drivers/media/pci/saa7146/hexium_gemini.c:257:12: error: stack frame size of 2304 bytes in function 'hexium_attach'
> [-Werror,-Wframe-larger-than=]
> static int hexium_attach(struct saa7146_dev *dev, struct saa7146_pci_extension_data *info)
> ^
>
> This one happens regardless of KASAN, and the problem is that a
> constructor to initalize a dynamically allocated structure leads
> to a copy of that structure on the stack, whereas gcc initializes
> it in place.
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=40776

oof, great bug report by the way! Thanks for the fix.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/media/pci/saa7146/hexium_gemini.c | 4 +---
> drivers/media/pci/saa7146/hexium_orion.c | 4 +---
> 2 files changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/pci/saa7146/hexium_gemini.c b/drivers/media/pci/saa7146/hexium_gemini.c
> index 5817d9cde4d0..f7ce0e1770bf 100644
> --- a/drivers/media/pci/saa7146/hexium_gemini.c
> +++ b/drivers/media/pci/saa7146/hexium_gemini.c
> @@ -270,9 +270,7 @@ static int hexium_attach(struct saa7146_dev *dev, struct saa7146_pci_extension_d
> /* enable i2c-port pins */
> saa7146_write(dev, MC1, (MASK_08 | MASK_24 | MASK_10 | MASK_26));
>
> - hexium->i2c_adapter = (struct i2c_adapter) {
> - .name = "hexium gemini",
> - };
> + strscpy(hexium->i2c_adapter.name, "hexium gemini", sizeof(hexium->i2c_adapter.name));
> saa7146_i2c_adapter_prepare(dev, &hexium->i2c_adapter, SAA7146_I2C_BUS_BIT_RATE_480);
> if (i2c_add_adapter(&hexium->i2c_adapter) < 0) {
> DEB_S("cannot register i2c-device. skipping.\n");
> diff --git a/drivers/media/pci/saa7146/hexium_orion.c b/drivers/media/pci/saa7146/hexium_orion.c
> index 0a05176c18ab..b9f4a09c744d 100644
> --- a/drivers/media/pci/saa7146/hexium_orion.c
> +++ b/drivers/media/pci/saa7146/hexium_orion.c
> @@ -231,9 +231,7 @@ static int hexium_probe(struct saa7146_dev *dev)
> saa7146_write(dev, DD1_STREAM_B, 0x00000000);
> saa7146_write(dev, MC2, (MASK_09 | MASK_25 | MASK_10 | MASK_26));
>
> - hexium->i2c_adapter = (struct i2c_adapter) {
> - .name = "hexium orion",
> - };
> + strscpy(hexium->i2c_adapter.name, "hexium orion", sizeof(hexium->i2c_adapter.name));

Note that "sparse" designated initialization zero initializes unnnamed members:
https://godbolt.org/z/LkSpJp
This transform you've done is safe because hexium was zero initialized
via kzalloc, and struct hexium contains a struct i2c_adapter (as
opposed to a pointer to a struct i2c_adapter). The same is true for
both translation units you've touched. LGTM

> saa7146_i2c_adapter_prepare(dev, &hexium->i2c_adapter, SAA7146_I2C_BUS_BIT_RATE_480);
> if (i2c_add_adapter(&hexium->i2c_adapter) < 0) {
> DEB_S("cannot register i2c-device. skipping.\n");
> --
> 2.20.0
>


--
Thanks,
~Nick Desaulniers

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