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Subject: Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON()
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To: Christophe Leroy <christophe.leroy@csgroup.eu>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
References: <20220624183238.388144-1-sv@linux.ibm.com>
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From: Sathvika Vasireddy <sv@linux.vnet.ibm.com>
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On 25/06/22 12:16, Christophe Leroy wrote:
>
> Le 24/06/2022 à 20:32, Sathvika Vasireddy a écrit :
>> objtool is throwing *unannotated intra-function call*
>> warnings with a few instructions that are marked
>> unreachable. Remove unreachable() from WARN_ON()
>> to fix these warnings, as the codegen remains same
>> with and without unreachable() in WARN_ON().
> Did you try the two exemples described in commit 1e688dd2a3d6
> ("powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with
> asm goto") ?
>
> Without your patch:
>
> 00000640 <test>:
>    640:	81 23 00 84 	lwz     r9,132(r3)
>    644:	71 29 40 00 	andi.   r9,r9,16384
>    648:	40 82 00 0c 	bne     654 <test+0x14>
>    64c:	80 63 00 0c 	lwz     r3,12(r3)
>    650:	4e 80 00 20 	blr
>    654:	0f e0 00 00 	twui    r0,0
>
> 00000658 <test9w>:
>    658:	2c 04 00 00 	cmpwi   r4,0
>    65c:	41 82 00 0c 	beq     668 <test9w+0x10>
>    660:	7c 63 23 96 	divwu   r3,r3,r4
>    664:	4e 80 00 20 	blr
>    668:	0f e0 00 00 	twui    r0,0
>    66c:	38 60 00 00 	li      r3,0
>    670:	4e 80 00 20 	blr
>
>
> With your patch:
>
> 00000640 <test>:
>    640:	81 23 00 84 	lwz     r9,132(r3)
>    644:	71 29 40 00 	andi.   r9,r9,16384
>    648:	40 82 00 0c 	bne     654 <test+0x14>
>    64c:	80 63 00 0c 	lwz     r3,12(r3)
>    650:	4e 80 00 20 	blr
>    654:	0f e0 00 00 	twui    r0,0
>    658:	4b ff ff f4 	b       64c <test+0xc>		<==
>
> 0000065c <test9w>:
>    65c:	2c 04 00 00 	cmpwi   r4,0
>    660:	41 82 00 0c 	beq     66c <test9w+0x10>
>    664:	7c 63 23 96 	divwu   r3,r3,r4
>    668:	4e 80 00 20 	blr
>    66c:	0f e0 00 00 	twui    r0,0
>    670:	38 60 00 00 	li      r3,0			<==
>    674:	4e 80 00 20 	blr				<==
>    678:	38 60 00 00 	li      r3,0
>    67c:	4e 80 00 20 	blr
>
The builtin variant of unreachable (__builtin_unreachable()) works,
and the codegen remains the same.

How about using that instead of unreachable() ?


- Sathvika

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    <p><br>
    </p>
    <div class="moz-cite-prefix"><font face="monospace">On 25/06/22
        12:16, Christophe Leroy wrote:</font><br>
    </div>
    <blockquote type="cite"
      cite="mid:70b6d08d-aced-7f4e-b958-a3c7ae1a9319@csgroup.eu">
      <pre class="moz-quote-pre" wrap="">

Le 24/06/2022 à 20:32, Sathvika Vasireddy a écrit :
</pre>
      <blockquote type="cite">
        <pre class="moz-quote-pre" wrap="">objtool is throwing *unannotated intra-function call*
warnings with a few instructions that are marked
unreachable. Remove unreachable() from WARN_ON()
to fix these warnings, as the codegen remains same
with and without unreachable() in WARN_ON().
</pre>
      </blockquote>
      <pre class="moz-quote-pre" wrap="">
Did you try the two exemples described in commit 1e688dd2a3d6 
("powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with 
asm goto") ?

Without your patch:

00000640 &lt;test&gt;:
  640:	81 23 00 84 	lwz     r9,132(r3)
  644:	71 29 40 00 	andi.   r9,r9,16384
  648:	40 82 00 0c 	bne     654 &lt;test+0x14&gt;
  64c:	80 63 00 0c 	lwz     r3,12(r3)
  650:	4e 80 00 20 	blr
  654:	0f e0 00 00 	twui    r0,0

00000658 &lt;test9w&gt;:
  658:	2c 04 00 00 	cmpwi   r4,0
  65c:	41 82 00 0c 	beq     668 &lt;test9w+0x10&gt;
  660:	7c 63 23 96 	divwu   r3,r3,r4
  664:	4e 80 00 20 	blr
  668:	0f e0 00 00 	twui    r0,0
  66c:	38 60 00 00 	li      r3,0
  670:	4e 80 00 20 	blr


With your patch:

00000640 &lt;test&gt;:
  640:	81 23 00 84 	lwz     r9,132(r3)
  644:	71 29 40 00 	andi.   r9,r9,16384
  648:	40 82 00 0c 	bne     654 &lt;test+0x14&gt;
  64c:	80 63 00 0c 	lwz     r3,12(r3)
  650:	4e 80 00 20 	blr
  654:	0f e0 00 00 	twui    r0,0
  658:	4b ff ff f4 	b       64c &lt;test+0xc&gt;		&lt;==

0000065c &lt;test9w&gt;:
  65c:	2c 04 00 00 	cmpwi   r4,0
  660:	41 82 00 0c 	beq     66c &lt;test9w+0x10&gt;
  664:	7c 63 23 96 	divwu   r3,r3,r4
  668:	4e 80 00 20 	blr
  66c:	0f e0 00 00 	twui    r0,0
  670:	38 60 00 00 	li      r3,0			&lt;==
  674:	4e 80 00 20 	blr				&lt;==
  678:	38 60 00 00 	li      r3,0
  67c:	4e 80 00 20 	blr

</pre>
    </blockquote>
    <font face="monospace">The builtin variant of unreachable (<font
        color="#151415"><span style="font-size: 12px; font-style: normal; font-variant-ligatures: none; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: left; text-indent: 0px; text-transform: none; white-space: pre-wrap; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgba(29, 28, 29, 0.04); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">__builtin_unreachable()</span></font>)
      works,</font><br>
    <font face="monospace">and the codegen remains the same. <br>
    </font>
    <p><font face="monospace">How about using that instead of
        unreachable() ?</font></p>
    <p><font face="monospace"><br>
      </font></p>
    <p><font face="monospace">- Sathvika<br>
      </font></p>
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