linux-kernel - [PATCH] ipmi_si: fix -Wvoid-pointer-to-enum-cast warning

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Date:   Wed, 09 Aug 2023 21:05:17 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Corey Minyard <minyard@....org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] ipmi_si: fix -Wvoid-pointer-to-enum-cast warning

With W=1 we see the following warning:

|  drivers/char/ipmi/ipmi_si_platform.c:272:15: error: \
|       cast to smaller integer type 'enum si_type' from \
|       'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]
|    272 |         io.si_type      = (enum si_type) match->data;
|        |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~

This is due to the fact that the `si_type` enum members are int-width
and a cast from pointer-width down to int will cause truncation and
possible data loss. Although in this case `si_type` has only a few
enumerated fields and thus there is likely no data loss occurring.
Nonetheless, this patch is necessary to the goal of promoting this
warning out of W=1.

Link: https://github.com/ClangBuiltLinux/linux/issues/1902
Link: https://lore.kernel.org/llvm/202308081000.tTL1ElTr-lkp@intel.com/
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note:
Arnd had mentioned that there perhaps may be some semantic differences
between GCC and Clang regarding this warning or family of warnings. For
now, this patch (and others following) will yield less noisy W=1 builds
and hopefully materialize into this warning getting promoted out of W=1
to an always-on warning.
---
 drivers/char/ipmi/ipmi_si_platform.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_si_platform.c b/drivers/char/ipmi/ipmi_si_platform.c
index 505cc978c97a..0d509d683c0f 100644
--- a/drivers/char/ipmi/ipmi_si_platform.c
+++ b/drivers/char/ipmi/ipmi_si_platform.c
@@ -269,7 +269,7 @@ static int of_ipmi_probe(struct platform_device *pdev)
 	}
 
 	memset(&io, 0, sizeof(io));
-	io.si_type	= (enum si_type) match->data;
+	io.si_type	= (unsigned long) match->data;
 	io.addr_source	= SI_DEVICETREE;
 	io.irq_setup	= ipmi_std_irq_setup;
 

---
base-commit: c1a515d3c0270628df8ae5f5118ba859b85464a2
change-id: 20230809-cbl-1902-7532a747b731

Best regards,
--
Justin Stitt <justinstitt@...gle.com>