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

From: [email-masked] (Xiaqing (A))
Date: Fri, 20 May 2016 11:22:40 +0800

? 2016/5/19 21:18, 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:
>>>
>>>
>>> ? 2016/5/19 18:49, Catalin Marinas ??:
>>>> 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
>

I have tested with your patch, the app still can not start up at all.

I'm sorry I didn't explan this exactly before, those apps are 32-bit 
android apps(com.tencent.pao etc.). They want to get the information as
   "*D m3e : GetCPUType:AArch64 Processor rev 0 (aarch64)*"
and I'm sure the process is forked by zygote not zygote64 in android M.

Finally, I find that apps need the information "Processor :", so when I 
change your patch as below, the apps can start up.
----------------------------------------------------------------------
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 3808470..f14ea4a 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -104,6 +104,8 @@ 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);
@@ -116,6 +118,10 @@ static int c_show(struct seq_file *m, void *v)
                  */
                 seq_printf(m, "processor\t: %d\n", i);

+               if (compat)
+                       seq_printf(m, "Processor\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),
                            loops_per_jiffy / (5000UL/HZ) % 100);
@@ -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))