linux-kernel - Re: [PATCH v2] net: stmmac: Avoid sometimes uninitialized Clang warnings

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Message-Id: <20190307.105938.496464522338008986.davem@davemloft.net>
Date:   Thu, 07 Mar 2019 10:59:38 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     natechancellor@...il.com
Cc:     peppe.cavallaro@...com, alexandre.torgue@...com,
        joabreu@...opsys.com, mcoquelin.stm32@...il.com,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, ndesaulniers@...gle.com
Subject: Re: [PATCH v2] net: stmmac: Avoid sometimes uninitialized Clang
 warnings

From: Nathan Chancellor <natechancellor@...il.com>
Date: Thu,  7 Mar 2019 11:00:28 -0700

> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:495:3: warning: variable 'ns' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:495:3: warning: variable 'ns' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:532:3: warning: variable 'ns' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:532:3: warning: variable 'ns' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:741:3: warning: variable 'sec_inc' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:741:3: warning: variable 'sec_inc' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
> 
> Clang is concerned with the use of stmmac_do_void_callback (which
> stmmac_get_timestamp and stmmac_config_sub_second_increment wrap),
> as it may fail to initialize these values if the if condition was ever
> false (meaning the callbacks don't exist). It's not wrong because the
> callbacks (get_timestamp and config_sub_second_increment respectively)
> are the ones that initialize the variables. While it's unlikely that the
> callbacks are ever going to disappear and make that condition false, we
> can easily avoid this warning by zero initialize the variables.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/384
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Applied.