linux-kernel - [PATCH] powerpc: Add HWCAP2 aux entry

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Date:	Thu, 18 Apr 2013 13:33:11 +1000
From:	Michael Neuling <mikey@...ling.org>
To:	Michael Ellerman <michael@...erman.id.au>,
	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	vda.linux@...glemail.com, Steve Munroe <sjmunroe@...ibm.com>,
	linux-kernel@...r.kernel.org, paulus@...ba.org,
	viro@...iv.linux.org.uk, Ryan Arnold <ryanarn@...ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, akpm@...ux-foundation.org
Subject: [PATCH] powerpc: Add HWCAP2 aux entry

We are currently out of free bits in AT_HWCAP. With POWER8, we have
several hardware features that we need to advertise. 

Tested on POWER and x86.

Signed-off-by: Michael Neuling <michael@...ling.org>
Signed-off-by: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
---

> Wouldn't it be safer to not emit AT_HWCAP2 unless it is defined by the arch?
> 
> That way the change would only impact powerpc.

Should be addressed with this version.

Mikey

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index fb3245e..ccadad6 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -52,6 +52,7 @@ struct cpu_spec {
 	char		*cpu_name;
 	unsigned long	cpu_features;		/* Kernel features */
 	unsigned int	cpu_user_features;	/* Userland features */
+	unsigned int	cpu_user_features2;	/* Userland features v2 */
 	unsigned int	mmu_features;		/* MMU features */
 
 	/* cache line sizes */
diff --git a/arch/powerpc/include/asm/elf.h b/arch/powerpc/include/asm/elf.h
index ac9790f..cc0655a 100644
--- a/arch/powerpc/include/asm/elf.h
+++ b/arch/powerpc/include/asm/elf.h
@@ -61,6 +61,7 @@ typedef elf_vrregset_t elf_fpxregset_t;
    instruction set this cpu supports.  This could be done in userspace,
    but it's not easy, and we've already done it here.  */
 # define ELF_HWCAP	(cur_cpu_spec->cpu_user_features)
+# define ELF_HWCAP2	(cur_cpu_spec->cpu_user_features2)
 
 /* This yields a string that ld.so will use to load implementation
    specific libraries for optimization.  This is more specific in
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 3939829..1f8b5d5 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -240,6 +240,9 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	NEW_AUX_ENT(AT_EGID, from_kgid_munged(cred->user_ns, cred->egid));
  	NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
 	NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);
+#ifdef ELF_HWCAP2
+	NEW_AUX_ENT(AT_HWCAP2, ELF_HWCAP2);
+#endif
 	NEW_AUX_ENT(AT_EXECFN, bprm->exec);
 	if (k_platform) {
 		NEW_AUX_ENT(AT_PLATFORM,
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 9c13e02..bf2381d 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -483,7 +483,6 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 	size_t platform_len = 0, len;
 	char *k_platform, *k_base_platform;
 	char __user *u_platform, *u_base_platform, *p;
-	long hwcap;
 	int loop;
 	int nr;	/* reset for each csp adjustment */
 
@@ -502,8 +501,6 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 		return -EFAULT;
 #endif
 
-	hwcap = ELF_HWCAP;
-
 	/*
 	 * If this architecture has a platform capability string, copy it
 	 * to userspace.  In some cases (Sparc), this info is impossible
@@ -617,7 +614,10 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
 
 	nr = 0;
 	csp -= DLINFO_ITEMS * 2 * sizeof(unsigned long);
-	NEW_AUX_ENT(AT_HWCAP,	hwcap);
+	NEW_AUX_ENT(AT_HWCAP,	ELF_HWCAP);
+#ifdef ELF_HWCAP2
+	NEW_AUX_ENT(AT_HWCAP2,	ELF_HWCAP2);
+#endif
 	NEW_AUX_ENT(AT_PAGESZ,	PAGE_SIZE);
 	NEW_AUX_ENT(AT_CLKTCK,	CLOCKS_PER_SEC);
 	NEW_AUX_ENT(AT_PHDR,	exec_params->ph_addr);
diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h
index 61594d5..835c065 100644
--- a/include/uapi/linux/auxvec.h
+++ b/include/uapi/linux/auxvec.h
@@ -28,6 +28,7 @@
 #define AT_BASE_PLATFORM 24	/* string identifying real platform, may
 				 * differ from AT_PLATFORM. */
 #define AT_RANDOM 25	/* address of 16 random bytes */
+#define AT_HWCAP2 26	/* extension of AT_HWCAP */
 
 #define AT_EXECFN  31	/* filename of program */
 
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