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[PATCH] i2c: designware: Remove i2c_dw_remove_lock_support()

Nathan Chancellor posted 1 patch 2 months ago 
drivers/i2c/busses/i2c-designware-core.h    |  1 -
drivers/i2c/busses/i2c-designware-platdrv.c | 11 -----------
2 files changed, 12 deletions(-)
[PATCH] i2c: designware: Remove i2c_dw_remove_lock_support()
Posted by Nathan Chancellor 2 months ago 
When building certain configurations with CONFIG_FINEIBT=y after
commit 894af4a1cde6 ("objtool: Validate kCFI calls"), there is a
warning due to an indirect call in dw_i2c_plat_remove():

  $ cat allno.config
  CONFIG_ACPI=y
  CONFIG_CFI=y
  CONFIG_COMMON_CLK=y
  CONFIG_CPU_MITIGATIONS=y
  CONFIG_I2C=y
  CONFIG_I2C_DESIGNWARE_BAYTRAIL=y
  CONFIG_I2C_DESIGNWARE_CORE=y
  CONFIG_I2C_DESIGNWARE_PLATFORM=y
  CONFIG_IOSF_MBI=y
  CONFIG_MITIGATION_RETPOLINE=y
  CONFIG_MODULES=y
  CONFIG_PCI=y
  CONFIG_X86_KERNEL_IBT=y

  $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean allnoconfig vmlinux
  vmlinux.o: warning: objtool: dw_i2c_plat_remove+0x3c: no-cfi indirect call!

With this configuration, i2c_dw_semaphore_cb_table has the BAYTRAIL
member and the sentinel (i.e., 2 members), both of which have an
implicit

  .remove = NULL,

so Clang effectively turns i2c_dw_remove_lock_support(), which is later
inlined into dw_i2c_plat_remove(), into:

  static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
  {
      if (dev->semaphore_idx > 2)
          (*NULL)(dev):
  }

which is not necessarily problematic from a logic perspective (as the
code was not bounds checking semaphore_idx so an out of bounds index
could already crash) but objtool's new __nocfi indirect call checking
trips over Clang dropping the kCFI setup from a known NULL indirect
call.

While it would be possible to fix this by transforming the initial check
into

  if (dev->semaphore_idx < 0 || dev->semaphore_idx >= ARRAY_SIZE(i2c_dw_semaphore_cb_table))

the remove member is unused after commit 440da737cf8d ("i2c: designware:
Use PCI PSP driver for communication"), so i2c_dw_remove_lock_support()
can be removed altogether, as it will never actually do anything.

Closes: https://github.com/ClangBuiltLinux/linux/issues/2133
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/i2c/busses/i2c-designware-core.h    |  1 -
 drivers/i2c/busses/i2c-designware-platdrv.c | 11 -----------
 2 files changed, 12 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index 347843b4f5dd..d50664377c6b 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -330,7 +330,6 @@ struct dw_i2c_dev {
 
 struct i2c_dw_semaphore_callbacks {
 	int	(*probe)(struct dw_i2c_dev *dev);
-	void	(*remove)(struct dw_i2c_dev *dev);
 };
 
 int i2c_dw_init_regmap(struct dw_i2c_dev *dev);
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 34d881572351..cff7e03dea7b 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -197,15 +197,6 @@ static int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev)
 	return 0;
 }
 
-static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
-{
-	if (dev->semaphore_idx < 0)
-		return;
-
-	if (i2c_dw_semaphore_cb_table[dev->semaphore_idx].remove)
-		i2c_dw_semaphore_cb_table[dev->semaphore_idx].remove(dev);
-}
-
 static int dw_i2c_plat_probe(struct platform_device *pdev)
 {
 	u32 flags = (uintptr_t)device_get_match_data(&pdev->dev);
@@ -339,8 +330,6 @@ static void dw_i2c_plat_remove(struct platform_device *pdev)
 
 	i2c_dw_prepare_clk(dev, false);
 
-	i2c_dw_remove_lock_support(dev);
-
 	reset_control_assert(dev->rst);
 }
 

---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251013-dw_i2c_plat_remove-avoid-objtool-no-cfi-warning-5f2040eaadc2

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>
Re: [PATCH] i2c: designware: Remove i2c_dw_remove_lock_support()
Posted by Andy Shevchenko 1 month, 3 weeks ago 
On Mon, Oct 13, 2025 at 06:05:03PM -0700, Nathan Chancellor wrote:
> When building certain configurations with CONFIG_FINEIBT=y after
> commit 894af4a1cde6 ("objtool: Validate kCFI calls"), there is a
> warning due to an indirect call in dw_i2c_plat_remove():
> 
>   $ cat allno.config
>   CONFIG_ACPI=y
>   CONFIG_CFI=y
>   CONFIG_COMMON_CLK=y
>   CONFIG_CPU_MITIGATIONS=y
>   CONFIG_I2C=y
>   CONFIG_I2C_DESIGNWARE_BAYTRAIL=y
>   CONFIG_I2C_DESIGNWARE_CORE=y
>   CONFIG_I2C_DESIGNWARE_PLATFORM=y
>   CONFIG_IOSF_MBI=y
>   CONFIG_MITIGATION_RETPOLINE=y
>   CONFIG_MODULES=y
>   CONFIG_PCI=y
>   CONFIG_X86_KERNEL_IBT=y
> 
>   $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean allnoconfig vmlinux
>   vmlinux.o: warning: objtool: dw_i2c_plat_remove+0x3c: no-cfi indirect call!
> 
> With this configuration, i2c_dw_semaphore_cb_table has the BAYTRAIL
> member and the sentinel (i.e., 2 members), both of which have an
> implicit
> 
>   .remove = NULL,
> 
> so Clang effectively turns i2c_dw_remove_lock_support(), which is later
> inlined into dw_i2c_plat_remove(), into:
> 
>   static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
>   {
>       if (dev->semaphore_idx > 2)
>           (*NULL)(dev):
>   }
> 
> which is not necessarily problematic from a logic perspective (as the
> code was not bounds checking semaphore_idx so an out of bounds index
> could already crash) but objtool's new __nocfi indirect call checking
> trips over Clang dropping the kCFI setup from a known NULL indirect
> call.
> 
> While it would be possible to fix this by transforming the initial check
> into
> 
>   if (dev->semaphore_idx < 0 || dev->semaphore_idx >= ARRAY_SIZE(i2c_dw_semaphore_cb_table))
> 
> the remove member is unused after commit 440da737cf8d ("i2c: designware:
> Use PCI PSP driver for communication"), so i2c_dw_remove_lock_support()
> can be removed altogether, as it will never actually do anything.

Have you seen this attempt to refactor a bit that code?

https://lore.kernel.org/linux-i2c/20231207141653.2785124-7-andriy.shevchenko@linux.intel.com/

-- 
With Best Regards,
Andy Shevchenko
Re: [PATCH] i2c: designware: Remove i2c_dw_remove_lock_support()
Posted by Nathan Chancellor 1 month, 3 weeks ago 
On Thu, Oct 23, 2025 at 09:29:02AM +0300, Andy Shevchenko wrote:
> Have you seen this attempt to refactor a bit that code?
> 
> https://lore.kernel.org/linux-i2c/20231207141653.2785124-7-andriy.shevchenko@linux.intel.com/

No, I did not. I did not look at historical attempts to fix this issue
since it was still present in -next.

Cheers,
Nathan
Re: [PATCH] i2c: designware: Remove i2c_dw_remove_lock_support()
Posted by Andi Shyti 2 months ago 
Hi Nathan,

On Mon, Oct 13, 2025 at 06:05:03PM -0700, Nathan Chancellor wrote:
> When building certain configurations with CONFIG_FINEIBT=y after
> commit 894af4a1cde6 ("objtool: Validate kCFI calls"), there is a
> warning due to an indirect call in dw_i2c_plat_remove():

...

> Closes: https://github.com/ClangBuiltLinux/linux/issues/2133
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

I'm OK with the "lengthy" (i.e. clear) message and I understood
that no r-b is binding. Applied to i2c/i2c-host.

Thanks,
Andi

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