linux-kernel - Re: next-20250903 x86_64 clang-20 allyesconfig mmp_pdma.c:1188:14: error: shift count >= width of type [-Werror,-Wshift-count-overflow]

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Message-ID: <aLgmpIlcBxH3klYp@stanley.mountain>
Date: Wed, 3 Sep 2025 14:29:40 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: clang-built-linux <llvm@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>, dmaengine@...r.kernel.org,
	lkft-triage@...ts.linaro.org,
	Linux Regressions <regressions@...ts.linux.dev>,
	Vinod Koul <vkoul@...nel.org>, Guodong Xu <guodong@...cstar.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Anders Roxell <anders.roxell@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Ben Copeland <benjamin.copeland@...aro.org>
Subject: Re: next-20250903 x86_64 clang-20 allyesconfig mmp_pdma.c:1188:14:
 error: shift count >= width of type [-Werror,-Wshift-count-overflow]

This seems like a clang-20 bug.  It's complaining about an impossible shift
in code which it should know is dead.

regards,
dan carpenter

On Wed, Sep 03, 2025 at 03:38:11PM +0530, Naresh Kamboju wrote:
> The following build warnings / errors were noticed on x86_64 allyesconfig
> with clang-20 toolchain running on Linux next-20250903 tag.
> 
> But the gcc-13 builds passed.
> 
> Regression Analysis:
> - New regression? yes
> - Reproducibility? yes
> 
> First seen on next-20250903
> Bad: next-20250903
> Good: next-20250902
> 
> Build regression: next-20250903 x86_64 clang-20 allyesconfig
> mmp_pdma.c:1188:14: error: shift count >= width of type
> [-Werror,-Wshift-count-overflow]
> 
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> 
> x86_64:
>   build:
>     * clang-20-allyesconfig
> 
> Build error:
> drivers/dma/mmp_pdma.c:1188:14: error: shift count >= width of type
> [-Werror,-Wshift-count-overflow]
>  1188 |         .dma_mask = DMA_BIT_MASK(64),   /* force 64-bit DMA
> addr capability */
>       |                     ^~~~~~~~~~~~~~~~
> include/linux/dma-mapping.h:73:54: note: expanded from macro 'DMA_BIT_MASK'
>    73 | #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
>       |                                                      ^ ~~~
> 1 error generated.
> make[5]: *** [scripts/Makefile.build:287: drivers/dma/mmp_pdma.o] Error 1
> 
> 
> ## Source
> * Kernel version: 6.17.0-rc4
> * Git tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git
> * Git describe: next-20250903
> * Git commit: 5d50cf9f7cf20a17ac469c20a2e07c29c1f6aab7
> * Architectures: x86_64
> * Toolchains: clang-20
> * Kconfigs: allyesconfig
> 
> ## Build
> * Build log: https://qa-reports.linaro.org/api/testruns/29752023/log_file/
> * Build details:
> https://regressions.linaro.org/lkft/linux-next-master/next-20250903/build/clang-20-allyesconfig/
> * Build plan: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/builds/32B39xPuITjxcbak13h2MrLZJP4
> * Build link: https://storage.tuxsuite.com/public/linaro/lkft/builds/32B39xPuITjxcbak13h2MrLZJP4/
> * Kernel config:
> https://storage.tuxsuite.com/public/linaro/lkft/builds/32B39xPuITjxcbak13h2MrLZJP4/config
> 
> --
> Linaro LKFT
> https://lkft.linaro.org