From mboxrd@z Thu Jan 1 00:00:00 1970 From: slash.tmp@free.fr (Mason) Date: Sun, 15 Mar 2015 18:40:28 +0100 Subject: read_cpuid_id() in arch/arm/kernel/setup.c In-Reply-To: <20150313164546.GV8656@n2100.arm.linux.org.uk> References: <55030A68.6070002@free.fr> <20150313161953.GS8656@n2100.arm.linux.org.uk> <550312BB.8020902@free.fr> <20150313164546.GV8656@n2100.arm.linux.org.uk> Message-ID: <5505C40C.1050001@free.fr> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 13/03/2015 17:45, Russell King - ARM Linux wrote: > Yes, this one I like - and it probably fixes a potential latent bug > where the compiler was free to re-order that mrc outside of the if() > statement. > > Please wrap it up as a normal submission, thanks. Proposed patch at the end of this message. I'm now puzzling over why it's required to have "memory" in read_cpuid_ext's clobber list, and not in read_cpuid's? Regards. -- >8 -- Date: Sun, 15 Mar 2015 17:59:53 +0100 Subject: [PATCH] Use read_cpuid_ext() macro instead of inline asm In commit 067e710b9a982a92cc8294d7fa0f1e924c65bba1, Paul Walmsley fixed read_cpuid_ext() and added the following comment. The memory clobber prevents gcc 4.5 from reordering the mrc before any is_smp() tests, which can cause undefined instruction aborts on ARM1136 r0 due to the missing extended CP15 registers. --- arch/arm/kernel/setup.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index e55408e..1d60beb 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -246,12 +246,9 @@ static int __get_cpu_architecture(void) if (cpu_arch) cpu_arch += CPU_ARCH_ARMv3; } else if ((read_cpuid_id() & 0x000f0000) == 0x000f0000) { - unsigned int mmfr0; - /* Revised CPUID format. Read the Memory Model Feature * Register 0 and check for VMSAv7 or PMSAv7 */ - asm("mrc p15, 0, %0, c0, c1, 4" - : "=r" (mmfr0)); + unsigned int mmfr0 = read_cpuid_ext(CPUID_EXT_MMFR0); if ((mmfr0 & 0x0000000f) >= 0x00000003 || (mmfr0 & 0x000000f0) >= 0x00000030) cpu_arch = CPU_ARCH_ARMv7; -- 2.3.2