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elf_aux.c

/*
 *  arch/um/kernel/elf_aux.c
 *
 *  Scan the Elf auxiliary vector provided by the host to extract
 *  information about vsyscall-page, etc.
 *
 *  Copyright (C) 2004 Fujitsu Siemens Computers GmbH
 *  Author: Bodo Stroesser (bodo.stroesser@fujitsu-siemens.com)
 */
#include <elf.h>
#include <stddef.h>
#include "init.h"
#include "elf_user.h"
#include "mem_user.h"
#include <kern_constants.h>

/* Use the one from the kernel - the host may miss it, if having old headers. */
#if UM_ELF_CLASS == UM_ELFCLASS32
typedef Elf32_auxv_t elf_auxv_t;
#else
typedef Elf64_auxv_t elf_auxv_t;
#endif

/* These are initialized very early in boot and never changed */
char * elf_aux_platform;
long elf_aux_hwcap;
unsigned long vsyscall_ehdr;
unsigned long vsyscall_end;
unsigned long __kernel_vsyscall;

__init void scan_elf_aux( char **envp)
{
      long page_size = 0;
      elf_auxv_t * auxv;

      while ( *envp++ != NULL) ;

      for ( auxv = (elf_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) {
            switch ( auxv->a_type ) {
                  case AT_SYSINFO:
                        __kernel_vsyscall = auxv->a_un.a_val;
                        /* See if the page is under TASK_SIZE */
                        if (__kernel_vsyscall < (unsigned long) envp)
                              __kernel_vsyscall = 0;
                        break;
                  case AT_SYSINFO_EHDR:
                        vsyscall_ehdr = auxv->a_un.a_val;
                        /* See if the page is under TASK_SIZE */
                        if (vsyscall_ehdr < (unsigned long) envp)
                              vsyscall_ehdr = 0;
                        break;
                  case AT_HWCAP:
                        elf_aux_hwcap = auxv->a_un.a_val;
                        break;
                  case AT_PLATFORM:
                                /* elf.h removed the pointer elements from
                                 * a_un, so we have to use a_val, which is
                                 * all that's left.
                                 */
                        elf_aux_platform =
                              (char *) (long) auxv->a_un.a_val;
                        break;
                  case AT_PAGESZ:
                        page_size = auxv->a_un.a_val;
                        break;
            }
      }
      if ( ! __kernel_vsyscall || ! vsyscall_ehdr ||
           ! elf_aux_hwcap || ! elf_aux_platform ||
           ! page_size || (vsyscall_ehdr % page_size) ) {
            __kernel_vsyscall = 0;
            vsyscall_ehdr = 0;
            elf_aux_hwcap = 0;
            elf_aux_platform = "i586";
      }
      else {
            vsyscall_end = vsyscall_ehdr + page_size;
      }
}

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