Re: [PATCH] arm64: cpuinfo: add AArch64 & elf platform for app compatibility

[Catalin Marinas]

On Thu, May 19, 2016 at 01:50:40PM +0100, Catalin Marinas wrote:
> On Thu, May 19, 2016 at 07:06:40PM +0800, Xiaqing (A) wrote:
> > 
> > 
> > å 2016/5/19 18:49, Catalin Marinas åé:
> > >On Thu, May 19, 2016 at 10:44:33AM +0800, x00195127 wrote:
> > >>we find that some apps will read cpuinfo when start up,
> > >>they need the string  as follows:
> > >>"Processor       : AArch64 Processor rev 0 (aarch64)"
> > >>
> > >>Then thay could load the corresponding libs. But now
> > >>arm64 platform's cpuinfo don't has this now, so
> > >>we need add this.
> > >
> > >I have the same question as Martinez: what are those apps? If they are
> > >64-bit apps, they can always assume AArch64 processor.
> > 
> > Those are 32-bit apps, and those apps are very popular in our country.
> 
> 32-bit apps checking for "AArch64" is a really silly idea. What do they
> do with this information?
> 
> I'm rather inclined to merge this patch:
> 
> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> index 3808470486f3..623d7d291dd6 100644
> --- a/arch/arm64/kernel/cpuinfo.c
> +++ b/arch/arm64/kernel/cpuinfo.c
> @@ -127,7 +127,8 @@ static int c_show(struct seq_file *m, void *v)
>  		 * software which does already (at least for 32-bit).
>  		 */
>  		seq_puts(m, "Features\t:");
> -		if (personality(current->personality) == PER_LINUX32) {
> +		if (is_compat_task() ||
> +		    personality(current->personality) == PER_LINUX32) {
>  #ifdef CONFIG_COMPAT
>  			for (j = 0; compat_hwcap_str[j]; j++)
>  				if (compat_elf_hwcap & (1 << j))

To make it even more in line with the AArch32 kernel, let's add the
"model name":

------------------8<---------------------
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 3808470486f3..6bda9d30a769 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -22,6 +22,7 @@
 
 #include <linux/bitops.h>
 #include <linux/bug.h>
+#include <linux/elf.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/personality.h>
@@ -104,6 +105,8 @@ static const char *const compat_hwcap2_str[] = {
 static int c_show(struct seq_file *m, void *v)
 {
 	int i, j;
+	bool compat = is_compat_task() ||
+		personality(current->personality) == PER_LINUX32;
 
 	for_each_online_cpu(i) {
 		struct cpuinfo_arm64 *cpuinfo = &per_cpu(cpu_data, i);
@@ -115,6 +118,9 @@ static int c_show(struct seq_file *m, void *v)
 		 * "processor".  Give glibc what it expects.
 		 */
 		seq_printf(m, "processor\t: %d\n", i);
+		if (compat)
+			seq_printf(m, "model name\t: ARMv8 Processor rev %d (%s)\n",
+				   MIDR_REVISION(midr), COMPAT_ELF_PLATFORM);
 
 		seq_printf(m, "BogoMIPS\t: %lu.%02lu\n",
 			   loops_per_jiffy / (500000UL/HZ),
@@ -127,7 +133,7 @@ static int c_show(struct seq_file *m, void *v)
 		 * software which does already (at least for 32-bit).
 		 */
 		seq_puts(m, "Features\t:");
-		if (personality(current->personality) == PER_LINUX32) {
+		if (compat) {
 #ifdef CONFIG_COMPAT
 			for (j = 0; compat_hwcap_str[j]; j++)
 				if (compat_elf_hwcap & (1 << j))
------------------8<---------------------

With the above, a compat task or a native one with PER_LINUX32
personality would get:

processor       : 0
model name      : ARMv8 Processor rev 0 (v8l)
BogoMIPS        : 100.00
Features        : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt lpae evtstrm aes pmull sha1 sha2 crc32
CPU implementer : 0x41
CPU architecture: 8
CPU variant     : 0x0
CPU part        : 0xd03
CPU revision    : 0

-- 
Catalin