blocks|key|2782483|text|解决方案1：使用diagnostic+pragmas，您可以在本地抑制某些诊断检查。在非空函数中抱怨不返回的特定选项(也由-Wall暗示)是-Wreturn-type。因此，禁止显示该警告的特定代码为：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2782484|#pragma+GCC+diagnostic+push
#pragma+GCC+diagnostic+ignored+"-Wreturn-type"
/*+Your+code+here+*/
#pragma+GCC+diagnostic+pop|code-block|syntax|javascript|2782485|您可以通过使用-fdiagnostics-show-option进行编译，找出是哪个选项导致了警告。它将简单地将选项附加到警告消息中。|2782486|解决方案2:定义一个register+variable并将其放入所需的寄存器中。引用inline+assembler+template中的变量，并生成以下代码：|2782487|uint32_t+fill_cache(void)
{
++register+uint32_t+cacheVal+__asm__+("r3");

++__asm__+__volatile__+("addi+%250,+0,+0"+:+"=r"+(cacheVal));
++/*+More+code+here+*/

++return+cacheVal;
}|2782488|易失性修改器是为了确保指令不会被移除或以某种其他方式受到优化策略的不希望的影响。|2782489|至少出于两个原因，首选解决方案2：|2782490|空函数no+returning非空函数的值是未定义的，只要标准是concerned.|2782491|There's+no+|unordered-list-item|2782492|(新的)诊断警告本来就不打算抑制。|ordered-list-item|2782493|2782494|2782495|entityMap|0|LINK|mutability|MUTABLE|url|http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html|1|http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html|2|http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html^0|0|5|8|I|0|0|0|0|0|6|A|H|1|16|P|2|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|F|3|G|5|H|7|1M|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1N|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|1O|8|@$9|1P|A|1Q|B|C]]|D|@$9|1R|A|1S|1|1T]|$9|1U|A|1V|1|1W]]|E|$]]|$1|O|3|P|5|H|7|1X|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|S|3|T|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|U|3|V|5|6|7|20|8|@]|D|@]|E|$]]|$1|W|3|X|5|Y|7|21|8|@]|D|@]|E|$]]|$1|Z|3|10|5|11|7|22|8|@]|D|@]|E|$]]|$1|12|3|-4|5|6|7|23|8|@]|D|@]|E|$]]|$1|13|3|-4|5|6|7|24|8|@]|D|@]|E|$]]|$1|14|3|-4|5|6|7|25|8|@]|D|@]|E|$]]]|15|$16|$5|17|18|19|E|$1A|1B]]|1C|$5|17|18|19|E|$1A|1D]]|1E|$5|17|18|19|E|$1A|1F]]]]

Solution 1: with <a href="http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html">diagnostic pragmas</a> you can locally suppress certain diagnostic checks. The specific option (which also is implied by -Wall) that complains for no return in a non-void function is -Wreturn-type. So the specific code to suppress the warning is:

<pre><code>#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wreturn-type"
/* Your code here */
#pragma GCC diagnostic pop
</code></pre>

You can find out which option is causing the warning by compiling with -fdiagnostics-show-option. It will simply append the option to the warning message.

Solution 2: define a <a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html">register variable</a> and put it in the desired register. Refer to the variable in an <a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html">inline assembler template</a>, with the resulting code:

<pre><code>uint32_t fill_cache(void)
{
 register uint32_t cacheVal __asm__ ("r3");

 __asm__ __volatile__ ("addi %0, 0, 0" : "=r" (cacheVal));
 /* More code here */

 return cacheVal;
}
</code></pre>

The volatile modifier is to ensure that the instruction is not removed or in some other way affected undesirably by the optimization strategy.

Solution 2 is preferred for at least two reasons:

<ol>
<li>The value of a no returning non-void function is undefined as far as the standard is concerned.</li>
<li>There's no risk of suppressing (new) diagnostic warnings there was no intention to suppress in the first place.</li>
</ol>

blocks|key|11375|text|函数可以声明为naked，在这种情况下，编译器不会生成prolog和epilog，并假设程序员保留了所有必要的寄存器，并在返回之前将输出值放入正确的寄存器中。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|11376|uint32_t+fill_cache(void)+__attribute__((naked));+//+Declaration
//+attribute+should+be+specified+in+declaration+not+in+implementation

uint32_t+fill_cache(void)+
{
++++__asm__+("addi+3,+0,+0\n");++/*+R3+=+0+*/
++++/*+More+asm+here+modifying+R3+and+filling+the+cache+lines.+*/
}|code-block|syntax|javascript|11377|有点晚了，但也许会有人插手这件事:)|11378|PS:据我所知，__asm__和__volatile__都是std=c89语法。实际上，在GNU+GCC中，__asm__和asm是没有区别的。但现代的方法是无底线的风格：asm+volatile。|11379|asm_language|11380|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/language/asm^0|7|5|0|0|0|8|7|G|C|U|7|1I|7|1Q|3|2E|C|0|0|C|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1G|8|@]|D|@$9|1H|A|1I|1|1J]]|E|$]]|$1|Q|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

Function could be declared as <code>naked</code>, in this case compiler would not generate prolog &amp; epilog and would assume that programmer preserves all necessary registers and puts output value into correct register(s) before return.

<pre><code>uint32_t fill_cache(void) __attribute__((naked)); // Declaration
// attribute should be specified in declaration not in implementation

uint32_t fill_cache(void) 
{
 __asm__ ("addi 3, 0, 0\n"); /* R3 = 0 */
 /* More asm here modifying R3 and filling the cache lines. */
}
</code></pre>

A bit late but maybe someone will step in this as well :)

PS: For my best knowledge <code>__asm__</code> as well as <code>__volatile__</code> are <code>std=c89</code> syntax. Practically there is not difference between <code>__asm__</code> &amp; <code>asm</code> in GNU GCC. But the modern approach is underscoreless style: <code>asm volatile</code>. 

<a href="http://en.cppreference.com/w/cpp/language/asm" rel="nofollow noreferrer">asm_language</a>

I have some PowerPC assembly code translated with a gcc cross compiler with this function:

<pre><code>uint32_t fill_cache(void)
{
 __asm__ ("addi 3, 0, 0\n"); /* R3 = 0 */
 /* More asm here modifying R3 and filling the cache lines. */
}
</code></pre>

which, under the PowerPC EABI, returns the value computed in R3. When compiling I get

<pre><code>foo.c:105: warning: control reaches end of non-void function
</code></pre>

Is there a way to teach gcc that a value is actually returned? Or is there a way to suppress the warning (without removing -Wall or adding -Wno-*)? I would like to very selectively suppress this warning for only this function in order to leave the general warning level as high as possible.

It is not an option to make this function return void since the value computed is required by the caller.

How to suppress "warning: control reaches end of non-void function"

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋 

腾讯云代码助手

CODING DevOps

Cloud Studio

SDK中心

API中心

命令行工具

我有一些用gcc交叉编译器编译的PowerPC汇编代码，其中包含以下函数：uint32_t fill_cache(void){    __asm__ ("addi 3, 0, 0\n");  /* R3 = 0 */    /* More asm here modifying R3 and filling the ca...

问如何抑制"warning: control到达非空函数结尾“
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何抑制"warning: control到达非空函数结尾“EN