Subject: Re: [PATCH] powerpc: Add HWCAP2 aux entry

From: Michael Neuling <[email-masked]>
Date: Thu, 18 Apr 2013 13:41:18 +1000

akpm,

If you're happy with this, is it something you can take in your tree?

Mikey

Michael Neuling <[email-masked]> wrote:
> 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 <[email-masked]>
> Signed-off-by: Nishanth Aravamudan <[email-masked]>
> ---
> 
> > 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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