linux-kernel - Re: [tip:x86/urgent 3/3] arch/x86/kernel/apic/apic.c:1182:6: warning: the address of 'x2apic

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Message-ID: <jpgwoezgldx.fsf@linux.bootlegged.copy>
Date:   Tue, 27 Aug 2019 02:42:02 -0400
From:   Bandan Das <bsd@...hat.com>
To:     kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        tipbuild@...or.com, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [tip:x86/urgent 3/3] arch/x86/kernel/apic/apic.c:1182:6: warning: the address of 'x2apic_enabled' will always evaluate as 'true'

kbuild test robot <lkp@...el.com> writes:

> tree:   https://kernel.googlesource.com/pub/scm/linux/kernel/git/tip/tip.git x86/urgent
> head:   cfa16294b1c5b320c0a0e1cac37c784b92366c87
> commit: cfa16294b1c5b320c0a0e1cac37c784b92366c87 [3/3] x86/apic: Include the LDR when clearing out APIC registers
> config: i386-defconfig (attached as .config)
> compiler: gcc-7 (Debian 7.4.0-10) 7.4.0
> reproduce:
>         git checkout cfa16294b1c5b320c0a0e1cac37c784b92366c87
>         # save the attached .config to linux build tree
>         make ARCH=i386 
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@...el.com>
>
> All warnings (new ones prefixed by >>):
>
>    arch/x86/kernel/apic/apic.c: In function 'clear_local_APIC':
>>> arch/x86/kernel/apic/apic.c:1182:6: warning: the address of 'x2apic_enabled' will always evaluate as 'true' [-Waddress]
>      if (!x2apic_enabled) {
>          ^
Thomas, I apologize for the typo here. This is the x2apic_enabled() function.
Should I respin ?

>
> vim +1182 arch/x86/kernel/apic/apic.c
>
>   1142	
>   1143	/*
>   1144	 * Local APIC start and shutdown
>   1145	 */
>   1146	
>   1147	/**
>   1148	 * clear_local_APIC - shutdown the local APIC
>   1149	 *
>   1150	 * This is called, when a CPU is disabled and before rebooting, so the state of
>   1151	 * the local APIC has no dangling leftovers. Also used to cleanout any BIOS
>   1152	 * leftovers during boot.
>   1153	 */
>   1154	void clear_local_APIC(void)
>   1155	{
>   1156		int maxlvt;
>   1157		u32 v;
>   1158	
>   1159		/* APIC hasn't been mapped yet */
>   1160		if (!x2apic_mode && !apic_phys)
>   1161			return;
>   1162	
>   1163		maxlvt = lapic_get_maxlvt();
>   1164		/*
>   1165		 * Masking an LVT entry can trigger a local APIC error
>   1166		 * if the vector is zero. Mask LVTERR first to prevent this.
>   1167		 */
>   1168		if (maxlvt >= 3) {
>   1169			v = ERROR_APIC_VECTOR; /* any non-zero vector will do */
>   1170			apic_write(APIC_LVTERR, v | APIC_LVT_MASKED);
>   1171		}
>   1172		/*
>   1173		 * Careful: we have to set masks only first to deassert
>   1174		 * any level-triggered sources.
>   1175		 */
>   1176		v = apic_read(APIC_LVTT);
>   1177		apic_write(APIC_LVTT, v | APIC_LVT_MASKED);
>   1178		v = apic_read(APIC_LVT0);
>   1179		apic_write(APIC_LVT0, v | APIC_LVT_MASKED);
>   1180		v = apic_read(APIC_LVT1);
>   1181		apic_write(APIC_LVT1, v | APIC_LVT_MASKED);
>> 1182		if (!x2apic_enabled) {
>   1183			v = apic_read(APIC_LDR) & ~APIC_LDR_MASK;
>   1184			apic_write(APIC_LDR, v);
>   1185		}
>   1186		if (maxlvt >= 4) {
>   1187			v = apic_read(APIC_LVTPC);
>   1188			apic_write(APIC_LVTPC, v | APIC_LVT_MASKED);
>   1189		}
>   1190	
>   1191		/* lets not touch this if we didn't frob it */
>   1192	#ifdef CONFIG_X86_THERMAL_VECTOR
>   1193		if (maxlvt >= 5) {
>   1194			v = apic_read(APIC_LVTTHMR);
>   1195			apic_write(APIC_LVTTHMR, v | APIC_LVT_MASKED);
>   1196		}
>   1197	#endif
>   1198	#ifdef CONFIG_X86_MCE_INTEL
>   1199		if (maxlvt >= 6) {
>   1200			v = apic_read(APIC_LVTCMCI);
>   1201			if (!(v & APIC_LVT_MASKED))
>   1202				apic_write(APIC_LVTCMCI, v | APIC_LVT_MASKED);
>   1203		}
>   1204	#endif
>   1205	
>   1206		/*
>   1207		 * Clean APIC state for other OSs:
>   1208		 */
>   1209		apic_write(APIC_LVTT, APIC_LVT_MASKED);
>   1210		apic_write(APIC_LVT0, APIC_LVT_MASKED);
>   1211		apic_write(APIC_LVT1, APIC_LVT_MASKED);
>   1212		if (maxlvt >= 3)
>   1213			apic_write(APIC_LVTERR, APIC_LVT_MASKED);
>   1214		if (maxlvt >= 4)
>   1215			apic_write(APIC_LVTPC, APIC_LVT_MASKED);
>   1216	
>   1217		/* Integrated APIC (!82489DX) ? */
>   1218		if (lapic_is_integrated()) {
>   1219			if (maxlvt > 3)
>   1220				/* Clear ESR due to Pentium errata 3AP and 11AP */
>   1221				apic_write(APIC_ESR, 0);
>   1222			apic_read(APIC_ESR);
>   1223		}
>   1224	}
>   1225	
>
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
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