Commit 483fad1c authored by Nathan Lynch's avatar Nathan Lynch Committed by Benjamin Herrenschmidt
Browse files

ELF loader support for auxvec base platform string 



Some IBM POWER-based platforms have the ability to run in a
mode which mostly appears to the OS as a different processor from the
actual hardware.  For example, a Power6 system may appear to be a
Power5+, which makes the AT_PLATFORM value "power5+".  This means that
programs are restricted to the ISA supported by Power5+;
Power6-specific instructions are treated as illegal.

However, some applications (virtual machines, optimized libraries) can
benefit from knowledge of the underlying CPU model.  A new aux vector
entry, AT_BASE_PLATFORM, will denote the actual hardware.  For
example, on a Power6 system in Power5+ compatibility mode, AT_PLATFORM
will be "power5+" and AT_BASE_PLATFORM will be "power6".  The idea is
that AT_PLATFORM indicates the instruction set supported, while
AT_BASE_PLATFORM indicates the underlying microarchitecture.

If the architecture has defined ELF_BASE_PLATFORM, copy that value to
the user stack in the same manner as ELF_PLATFORM.

Signed-off-by: default avatarNathan Lynch <ntl@pobox.com>
Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent e9f76354

fs/binfmt_elf.c

+28 −0
Original line number Diff line number Diff line
@@ -131,6 +131,15 @@ static int padzero(unsigned long elf_bss) 
#define STACK_ALLOC(sp, len) ({ sp -= len ; sp; })

#endif



#ifndef ELF_BASE_PLATFORM

/*

 * AT_BASE_PLATFORM indicates the "real" hardware/microarchitecture.

 * If the arch defines ELF_BASE_PLATFORM (in asm/elf.h), the value

 * will be copied to the user stack in the same manner as AT_PLATFORM.

 */

#define ELF_BASE_PLATFORM NULL

#endif



static int

create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,

		unsigned long load_addr, unsigned long interp_load_addr)
@@ -142,7 +151,9 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, 
	elf_addr_t __user *envp;

	elf_addr_t __user *sp;

	elf_addr_t __user *u_platform;

	elf_addr_t __user *u_base_platform;

	const char *k_platform = ELF_PLATFORM;

	const char *k_base_platform = ELF_BASE_PLATFORM;

	int items;

	elf_addr_t *elf_info;

	int ei_index = 0;
@@ -172,6 +183,19 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, 
			return -EFAULT;

	}



	/*

	 * If this architecture has a "base" platform capability

	 * string, copy it to userspace.

	 */

	u_base_platform = NULL;

	if (k_base_platform) {

		size_t len = strlen(k_base_platform) + 1;



		u_base_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);

		if (__copy_to_user(u_base_platform, k_base_platform, len))

			return -EFAULT;

	}



	/* Create the ELF interpreter info */

	elf_info = (elf_addr_t *)current->mm->saved_auxv;

	/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
@@ -209,6 +233,10 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, 
		NEW_AUX_ENT(AT_PLATFORM,

			    (elf_addr_t)(unsigned long)u_platform);

	}

	if (k_base_platform) {

		NEW_AUX_ENT(AT_BASE_PLATFORM,

			    (elf_addr_t)(unsigned long)u_base_platform);

	}

	if (bprm->interp_flags & BINPRM_FLAGS_EXECFD) {

		NEW_AUX_ENT(AT_EXECFD, bprm->interp_data);

	}

include/linux/auxvec.h

+5 −1
Original line number Diff line number Diff line
@@ -26,9 +26,13 @@ 


#define AT_SECURE 23   /* secure mode boolean */



#define AT_BASE_PLATFORM 24	/* string identifying real platform, may

				 * differ from AT_PLATFORM. */



#define AT_EXECFN  31	/* filename of program */



#ifdef __KERNEL__

#define AT_VECTOR_SIZE_BASE 17 /* NEW_AUX_ENT entries in auxiliary table */

#define AT_VECTOR_SIZE_BASE 18 /* NEW_AUX_ENT entries in auxiliary table */

  /* number of "#define AT_.*" above, minus {AT_NULL, AT_IGNORE, AT_NOTELF} */

#endif

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