On Thu, Aug 11, 2016 at 10:53:01AM +0200, Arnd Bergmann wrote:

On Thursday, August 11, 2016 3:35:01 PM CEST Zhangjian (Bamvor) wrote:

quoted

On 2016/6/18 7:54, Yury Norov wrote:

quoted

From: Andrew Pinski <redacted>

In this patchset  ILP32 ABI support is added. Additionally to AARCH32,
which is binary-compatible with ARM, ILP32 is (mostly) ABI-compatible.

 From now, AARCH32_EL0 (former COMPAT) config option means the support of
AARCH32 userspace, ARM64_ILP32 - support of ILP32 ABI (see next patches),
and COMPAT indicates that one of them, or both, is enabled.

Where needed, CONFIG_COMPAT is changed over to use CONFIG_AARCH32_EL0 instead

Reviewed-by: David Daney <redacted>
Signed-off-by: Andrew Pinski <redacted>
Signed-off-by: Philipp Tomsich <redacted>
Signed-off-by: Christoph Muellner <redacted>
Signed-off-by: Bamvor Jian Zhang <redacted>
Signed-off-by: Yury Norov <redacted>

...

quoted

diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index c173d32..af200a8 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c

@@ -134,15 +134,17 @@ static int c_show(struct seq_file *m, void *v)
  		 */
  		seq_puts(m, "Features\t:");
  		if (compat) {
-#ifdef CONFIG_COMPAT
-			for (j = 0; compat_hwcap_str[j]; j++)
-				if (compat_elf_hwcap & (1 << j))
-					seq_printf(m, " %s", compat_hwcap_str[j]);
-
-			for (j = 0; compat_hwcap2_str[j]; j++)
-				if (compat_elf_hwcap2 & (1 << j))
-					seq_printf(m, " %s", compat_hwcap2_str[j]);
-#endif /* CONFIG_COMPAT */
+#ifdef CONFIG_AARCH32_EL0

I saw that compat_hwcap_str and compat_hwcap2_str is defined when
"CONFIG_COMPAT" is true. Why we only change it to CONFIG_AARCH32_EL0
in c show()?

quoted

+			if (personality(current->personality) == PER_LINUX32) {

And "compat" is "personality(current->personality) == PER_LINUX32;",
it seems that there is no need to add this twice.

I think it would be best to remove the #ifdef here completely,
the PER_LINUX32 concept is not strictly tied to the emulation
of ARM binaries, it literally just changes the output of
/proc/cpuinfo and 'uname',

It's not strictly related to ARM binaries, however it is related to
AArch32 CPU features being supported and detected by the kernel.
Currently, with CONFIG_COMPAT disabled, we won't have access to a
(meaningful) compat_elf_hwcap.

and you can have ARM binaries with
PER_LINUX (using the arm64 uname) just like you can have
arm64 binaries running with PER_LINUX32.

I was actually looking to enforce the 32-bit binaries to only see
PER_LINUX32, though with a risk of breaking the ABI. OTOH, people are
abusing this and write 32-bit apps relying on the 64-bit /proc/cpuinfo:

http://lkml.kernel.org/g/1464706504-25224-3-git-send-email-catalin.marinas@arm.com

(you were summoned on that discussion couple of times ;))

-- 
Catalin