amd64-hook-ia32-table-20030521
[openafs.git] / src / afs / LINUX / osi_module.c
index e51a5fa..a3a05f9 100644 (file)
@@ -21,30 +21,40 @@ RCSID("$Header$");
 #include "h/unistd.h" /* For syscall numbers. */
 #include "h/mm.h"
 
+#ifdef AFS_AMD64_LINUX20_ENV
+#include "../asm/ia32_unistd.h"
+#endif
+
 #include <linux/module.h>
 #include <linux/slab.h>
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,4,0)
 #include <linux/init.h>
+#include <linux/sched.h>
+#endif
+#if !defined(EXPORTED_SYS_CALL_TABLE) && defined(HAVE_KERNEL_LINUX_SYSCALL_H)
+#include <linux/syscall.h>
 #endif
-
-
 
 #ifdef AFS_SPARC64_LINUX24_ENV
 #define __NR_setgroups32      82 /* This number is not exported for some bizarre reason. */
 #endif
 
 asmlinkage int (*sys_settimeofdayp)(struct timeval *tv, struct timezone *tz);
-#if !defined(AFS_ALPHA_LINUX20_ENV)
-asmlinkage int (*sys_socketcallp)(int call, long *args);
-#endif /* no socketcall on alpha */
-asmlinkage int (*sys_killp)(int pid, int signal);
 asmlinkage long (*sys_setgroupsp)(int gidsetsize, gid_t *grouplist);
 
+#ifdef EXPORTED_SYS_CALL_TABLE
 #ifdef AFS_SPARC64_LINUX20_ENV
 extern unsigned int sys_call_table[];  /* changed to uint because SPARC64 has syscaltable of 32bit items */
 #else
 extern void * sys_call_table[]; /* safer for other linuces */
 #endif
+#else /* EXPORTED_SYS_CALL_TABLE */
+#ifdef AFS_SPARC64_LINUX20_ENV
+static unsigned int *sys_call_table;  /* changed to uint because SPARC64 has syscaltable of 32bit items */
+#else
+static void ** sys_call_table; /* safer for other linuces */
+#endif
+#endif
 extern struct file_system_type afs_file_system;
 
 static long get_page_offset(void);
@@ -66,96 +76,108 @@ static unsigned int afs_ni_syscall = 0;
 static void* afs_ni_syscall = 0;
 #endif
  
+#ifdef AFS_AMD64_LINUX20_ENV
+#ifdef EXPORTED_IA32_SYS_CALL_TABLE
+extern void * ia32_sys_call_table[];
+#else
+static void **ia32_sys_call_table;
+#endif
+
+static void *ia32_ni_syscall = 0;
+asmlinkage long (*sys32_setgroupsp)(int gidsetsize, old_gid_t *grouplist);
+#if defined(__NR_ia32_setgroups32)
+asmlinkage long (*sys32_setgroups32p)(int gidsetsize, gid_t *grouplist);
+#endif /* __NR_ia32_setgroups32 */
+#endif /* AFS_AMD64_LINUX20_ENV */
+
 #ifdef AFS_SPARC64_LINUX20_ENV
 static unsigned int afs_ni_syscall32 = 0;
 asmlinkage int (*sys32_setgroupsp)(int gidsetsize, __kernel_gid_t32 *grouplist);
 #if defined(__NR_setgroups32)
 asmlinkage int (*sys32_setgroups32p)(int gidsetsize, __kernel_gid_t32 *grouplist);
-#endif
+#endif /* __NR_setgroups32 */
+#ifdef EXPORTED_SYS_CALL_TABLE
 extern unsigned int sys_call_table32[];
+#else /* EXPORTED_SYS_CALL_TABLE */
+static unsigned int *sys_call_table32;
+#endif /* EXPORTED_SYS_CALL_TABLE */
 
 asmlinkage int afs_syscall32(long syscall, long parm1, long parm2, long parm3,
                             long parm4, long parm5)
 {
-__asm__ __volatile__ ("
-       srl %o4, 0, %o4
-       mov %o7, %i7
-       call afs_syscall
-       srl %o5, 0, %o5
-       ret
-       nop
-");
+__asm__ __volatile__ ("srl %o4, 0, %o4\n\t"
+                      "mov %o7, %i7\n\t"
+                      "call afs_syscall\n\t"
+                     "srl %o5, 0, %o5\n\t"
+                     "ret\n\t"
+                      "nop");
 }
-#endif
+#endif /* AFS_SPARC64_LINUX20_ENV */
 
 #ifdef AFS_IA64_LINUX20_ENV
 
 asmlinkage long
 afs_syscall_stub(int r0, int r1, long r2, long r3, long r4, long gp)
 {
-__asm__ __volatile__ ("
-        alloc r42 = ar.pfs, 8, 3, 6, 0
-        mov r41 = b0                   /* save rp */
-        mov out0 = in0
-        mov out1 = in1
-        mov out2 = in2
-        mov out3 = in3
-        mov out4 = in4
-        mov out5 = gp                  /* save gp */
-        ;;
-.L1:    mov r3 = ip
-        ;;
-        addl r15=.fptr_afs_syscall-.L1,r3
-        ;;
-        ld8 r15=[r15]
-        ;;
-        ld8 r16=[r15],8
-        ;;
-        ld8 gp=[r15]
-        mov b6=r16
-        br.call.sptk.many b0 = b6
-        ;;
-        mov ar.pfs = r42
-        mov b0 = r41
-        mov gp = r48                   /* restore gp */
-        br.ret.sptk.many b0
-.fptr_afs_syscall:
-        data8 @fptr(afs_syscall)
-");
+__asm__ __volatile__ ("alloc r42 = ar.pfs, 8, 3, 6, 0\n\t"
+                      "mov r41 = b0\n\t"                /* save rp */
+                      "mov out0 = in0\n\t"
+                      "mov out1 = in1\n\t"
+                      "mov out2 = in2\n\t"
+                      "mov out3 = in3\n\t"
+                      "mov out4 = in4\n\t"
+                      "mov out5 = gp\n\t"                       /* save gp */
+                      ";;\n"
+                      ".L1:    mov r3 = ip\n\t"
+                      ";;\n\t"
+                      "addl r15=.fptr_afs_syscall-.L1,r3\n\t"
+                      ";;\n\t"
+                      "ld8 r15=[r15]\n\t"
+                      ";;\n\t"
+                      "ld8 r16=[r15],8\n\t"
+                      ";;\n\t"
+                      "ld8 gp=[r15]\n\t"
+                      "mov b6=r16\n\t"
+                      "br.call.sptk.many b0 = b6\n\t"
+                      ";;\n\t"
+                      "mov ar.pfs = r42\n\t"
+                      "mov b0 = r41\n\t"
+                      "mov gp = r48\n\t"                /* restore gp */
+                      "br.ret.sptk.many b0\n"
+                      ".fptr_afs_syscall:\n\t"
+                      "data8 @fptr(afs_syscall)");
 }
 
 asmlinkage long
 afs_xsetgroups_stub(int r0, int r1, long r2, long r3, long r4, long gp)
 {
-__asm__ __volatile__ ("
-        alloc r42 = ar.pfs, 8, 3, 6, 0
-        mov r41 = b0                   /* save rp */
-        mov out0 = in0
-        mov out1 = in1
-        mov out2 = in2
-        mov out3 = in3
-        mov out4 = in4
-        mov out5 = gp                  /* save gp */
-        ;;
-.L2:    mov r3 = ip
-        ;;
-        addl r15=.fptr_afs_xsetgroups - .L2,r3
-        ;;
-        ld8 r15=[r15]
-        ;;
-        ld8 r16=[r15],8
-        ;;
-        ld8 gp=[r15]
-        mov b6=r16
-        br.call.sptk.many b0 = b6
-        ;;
-        mov ar.pfs = r42
-        mov b0 = r41
-        mov gp = r48                   /* restore gp */
-        br.ret.sptk.many b0
-.fptr_afs_xsetgroups:
-        data8 @fptr(afs_xsetgroups)
-");
+__asm__ __volatile__ ("alloc r42 = ar.pfs, 8, 3, 6, 0\n\t"
+                      "mov r41 = b0\n\t"                /* save rp */
+                      "mov out0 = in0\n\t"
+                      "mov out1 = in1\n\t"
+                      "mov out2 = in2\n\t"
+                      "mov out3 = in3\n\t"
+                      "mov out4 = in4\n\t"
+                      "mov out5 = gp\n\t"                       /* save gp */
+                      ";;\n"
+                      ".L2:    mov r3 = ip\n\t"
+                      ";;\n\t"
+                      "addl r15=.fptr_afs_xsetgroups - .L2,r3\n\t"
+                      ";;\n\t"
+                      "ld8 r15=[r15]\n\t"
+                      ";;\n\t"
+                      "ld8 r16=[r15],8\n\t"
+                      ";;\n\t"
+                      "ld8 gp=[r15]\n\t"
+                      "mov b6=r16\n\t"
+                      "br.call.sptk.many b0 = b6\n\t"
+                      ";;\n\t"
+                      "mov ar.pfs = r42\n\t"
+                      "mov b0 = r41\n\t"
+                      "mov gp = r48\n\t"                /* restore gp */
+                      "br.ret.sptk.many b0\n"
+                      ".fptr_afs_xsetgroups:\n\t"
+                      "data8 @fptr(afs_xsetgroups)");
 }
 
 struct fptr
@@ -168,7 +190,7 @@ struct fptr
 
 #ifdef AFS_LINUX24_ENV
 asmlinkage int (*sys_setgroups32p)(int gidsetsize, __kernel_gid32_t *grouplist);
-#endif 
+#endif /* AFS_LINUX24_ENV */
 
 #ifdef AFS_SPARC64_LINUX20_ENV
 #define POINTER2SYSCALL (unsigned int)(unsigned long)
@@ -186,19 +208,39 @@ int init_module(void)
 {
 #if defined(AFS_IA64_LINUX20_ENV)
     unsigned long kernel_gp;
-    static struct fptr sys_kill, sys_settimeofday, sys_setgroups;
+    static struct fptr sys_settimeofday, sys_setgroups;
 #endif
     extern int afs_syscall();
     extern long afs_xsetgroups();
 #if defined(__NR_setgroups32)
     extern int afs_xsetgroups32();
-#endif
-#ifdef AFS_SPARC64_LINUX20_ENV
+#endif /* __NR_setgroups32 */
+#if defined(AFS_SPARC64_LINUX20_ENV) || defined (AFS_AMD64_LINUX20_ENV)
     extern int afs32_xsetgroups();
-#if defined(__NR_setgroups32)
+#if (defined(__NR_setgroups32) && defined(AFS_SPARC64_LINUX20_ENV))
     extern int afs32_xsetgroups32();
 #endif
+#if (defined(__NR_ia32_setgroups32) && defined(AFS_AMD64_LINUX20_ENV))
+    extern int afs32_xsetgroups32();
 #endif
+#endif /* AFS_SPARC64_LINUX20_ENV || AFS_AMD64_LINUX20_ENV */
+
+#if !defined(EXPORTED_SYS_CALL_TABLE) || (defined(AFS_AMD64_LINUX20_ENV) && !defined(EXPORTED_IA32_SYS_CALL_TABLE))
+    unsigned long *ptr;
+    unsigned long offset;
+    unsigned long datalen;
+    int ret;
+    unsigned long token;
+    char      *mod_name;
+    unsigned long    mod_start;
+    unsigned long    mod_end;
+    char      *sec_name;
+    unsigned long    sec_start;
+    unsigned long    sec_end;
+    char      *sym_name;
+    unsigned long    sym_start;
+    unsigned long    sym_end;
+#endif /* EXPORTED_SYS_CALL_TABLE */
 
     RWLOCK_INIT(&afs_xosi, "afs_xosi");
 
@@ -212,27 +254,170 @@ int init_module(void)
         return -EIO;
     }
 #endif
+#ifndef EXPORTED_SYS_CALL_TABLE
+    sys_call_table=0;
+
+#ifdef EXPORTED_KALLSYMS_SYMBOL
+    ret=1;
+    token=0;
+    while (ret) {
+      sym_start=0;
+      ret=kallsyms_symbol_to_address("sys_call_table", &token, &mod_name,
+                                    &mod_start, &mod_end, &sec_name, &sec_start, &sec_end,
+                                    &sym_name, &sym_start, &sym_end);
+      if (ret && !strcmp(mod_name, "kernel"))
+       break;
+    }
+    if (ret && sym_start) {
+      sys_call_table=sym_start;
+    }
+#else
+#ifdef EXPORTED_KALLSYMS_ADDRESS
+    ret=kallsyms_address_to_symbol((unsigned long)&init_mm, &mod_name,
+                                  &mod_start, &mod_end, &sec_name, &sec_start, &sec_end,
+                                  &sym_name, &sym_start, &sym_end);
+    ptr=(unsigned long *)sec_start;
+    datalen=(sec_end-sec_start)/sizeof(unsigned long);
+#else
+#if defined(AFS_IA64_LINUX20_ENV)
+    ptr = (unsigned long *) (&sys_close - 0x180000);
+    datalen=0x180000/sizeof(ptr);
+#else
+#if defined(AFS_AMD64_LINUX20_ENV)
+    ptr=(unsigned long *)&init_mm;
+    datalen=0x180000/sizeof(ptr);
+#else
+    ptr=(unsigned long *)&init_mm;
+    datalen=16384;
+#endif
+#endif
+#endif
+    for (offset=0;offset <datalen;ptr++,offset++) {
+#if defined(AFS_IA64_LINUX20_ENV)
+       unsigned long close_ip=(unsigned long) ((struct fptr *)&sys_close)->ip;
+       unsigned long chdir_ip=(unsigned long) ((struct fptr *)&sys_chdir)->ip;
+       unsigned long write_ip=(unsigned long) ((struct fptr *)&sys_write)->ip;
+       if (ptr[0] == close_ip &&
+           ptr[__NR_chdir - __NR_close] == chdir_ip &&
+           ptr[__NR_write - __NR_close] == write_ip) {
+           sys_call_table=(void *) &(ptr[ -1 * (__NR_close-1024)]);
+           break;
+       }
+#else
+#if defined(EXPORTED_SYS_WAIT4) && defined(EXPORTED_SYS_CLOSE)
+        if (ptr[0] == (unsigned long)&sys_close &&
+            ptr[__NR_wait4 - __NR_close] == (unsigned long)&sys_wait4) {
+            sys_call_table=ptr - __NR_close;
+            break;
+        }
+#else
+#if defined(EXPORTED_SYS_CHDIR) && defined(EXPORTED_SYS_CLOSE)
+        if (ptr[0] == (unsigned long)&sys_close &&
+           ptr[__NR_chdir - __NR_close] == (unsigned long)&sys_chdir) {
+           sys_call_table=ptr - __NR_close;
+           break;
+       }
+#else
+       if (ptr[0] == (unsigned long)&sys_exit &&
+           ptr[__NR_open - __NR_exit] == (unsigned long)&sys_open) {
+           sys_call_table=ptr - __NR_exit;
+           break;
+       }
+#endif
+#endif
+#endif
+    }
+#ifdef EXPORTED_KALLSYMS_ADDRESS
+    ret=kallsyms_address_to_symbol((unsigned long)sys_call_table, &mod_name,
+                                  &mod_start, &mod_end, &sec_name, &sec_start, &sec_end,
+                                  &sym_name, &sym_start, &sym_end);
+    if (ret && strcmp(sym_name, "sys_call_table"))
+      sys_call_table=0;
+#endif
+#endif
+    if (!sys_call_table) {
+      printf("Failed to find address of sys_call_table\n");
+      return -EIO;
+    }
+    printf("Found sys_call_table at %x\n", sys_call_table);
+# ifdef AFS_SPARC64_LINUX20_ENV
+    error cant support this yet.
+#endif
+#endif /* EXPORTED_SYS_CALL_TABLE */
+      
+#ifdef AFS_AMD64_LINUX20_ENV
+#ifndef EXPORTED_IA32_SYS_CALL_TABLE
+    ia32_sys_call_table=0;
+#ifdef EXPORTED_KALLSYMS_SYMBOL
+    ret=1;
+    token=0;
+    while (ret) {
+       sym_start=0;
+       ret=kallsyms_symbol_to_address("ia32_sys_call_table", &token, 
+                                      &mod_name, &mod_start, &mod_end, 
+                                      &sec_name, &sec_start, &sec_end,
+                                      &sym_name, &sym_start, &sym_end);
+       if (ret && !strcmp(mod_name, "kernel"))
+               break;
+    }
+    if (ret && sym_start) {
+           ia32_sys_call_table=sym_start;
+    }
+#else /* EXPORTED_KALLSYMS_SYMBOL */
+#ifdef EXPORTED_KALLSYMS_ADDRESS
+    ret=kallsyms_address_to_symbol((unsigned long)&interruptible_sleep_on, 
+                                  &mod_name, &mod_start, &mod_end, &sec_name,
+                                  &sec_start, &sec_end,
+                                  &sym_name, &sym_start, &sym_end);
+    ptr=(unsigned long *)sec_start;
+    datalen=(sec_end-sec_start)/sizeof(unsigned long);
+#else /* EXPORTED_KALLSYMS_ADDRESS */
+#if defined(AFS_AMD64_LINUX20_ENV)
+    ptr=(unsigned long *)&interruptible_sleep_on;
+    datalen=0x180000/sizeof(ptr);
+#else /* AFS_AMD64_LINUX20_ENV */
+    ptr=(unsigned long *)&interruptible_sleep_on;
+    datalen=16384;
+#endif /* AFS_AMD64_LINUX20_ENV */
+#endif /* EXPORTED_KALLSYMS_ADDRESS */
+    for (offset=0;offset <datalen;ptr++,offset++) {
+        if (ptr[0] == (unsigned long)&sys_exit &&
+           ptr[__NR_ia32_open - __NR_ia32_exit] == (unsigned long)&sys_open) {
+               ia32_sys_call_table=ptr - __NR_ia32_exit;
+           break;
+       }
+    }
+#ifdef EXPORTED_KALLSYMS_ADDRESS
+    ret=kallsyms_address_to_symbol((unsigned long)ia32_sys_call_table, 
+                                  &mod_name, &mod_start, &mod_end, &sec_name,
+                                  &sec_start, &sec_end,
+                                  &sym_name, &sym_start, &sym_end);
+    if (ret && strcmp(sym_name, "ia32_sys_call_table"))
+            ia32_sys_call_table=0;
+#endif /* EXPORTED_KALLSYMS_ADDRESS */
+#endif /* EXPORTED_KALLSYMS_SYMBOL */
+    if (!ia32_sys_call_table) {
+         printf("Warning: Failed to find address of ia32_sys_call_table\n");
+    } else {
+        printf("Found ia32_sys_call_table at %x\n", ia32_sys_call_table);
+    }
+#else
+    printf("Found ia32_sys_call_table at %x\n", ia32_sys_call_table);
+#endif /* IA32_SYS_CALL_TABLE */
+#endif
 
     /* Initialize pointers to kernel syscalls. */
 #if defined(AFS_IA64_LINUX20_ENV)
     kernel_gp = ((struct fptr *)printk)->gp;
 
     sys_settimeofdayp = (void *) &sys_settimeofday;
-    sys_killp = (void *) &sys_kill;
 
     ((struct fptr *)sys_settimeofdayp)->ip =
                SYSCALL2POINTER sys_call_table[__NR_settimeofday - 1024];
     ((struct fptr *)sys_settimeofdayp)->gp = kernel_gp;
     
-    ((struct fptr *)sys_killp)->ip =
-               SYSCALL2POINTER sys_call_table[__NR_kill - 1024];
-    ((struct fptr *)sys_killp)->gp = kernel_gp;
 #else /* !AFS_IA64_LINUX20_ENV */
     sys_settimeofdayp = SYSCALL2POINTER sys_call_table[__NR_settimeofday];
-#ifdef __NR_socketcall
-    sys_socketcallp = SYSCALL2POINTER sys_call_table[__NR_socketcall];
-#endif /* no socketcall on alpha */
-    sys_killp = SYSCALL2POINTER sys_call_table[__NR_kill];
 #endif /* AFS_IA64_LINUX20_ENV */
 
     /* setup AFS entry point. */
@@ -247,7 +432,6 @@ int init_module(void)
        return -EBUSY;
     }
 
-
 #if defined(AFS_IA64_LINUX20_ENV)
     afs_ni_syscall = sys_call_table[__NR_afs_syscall - 1024];
     sys_call_table[__NR_afs_syscall - 1024] = POINTER2SYSCALL ((struct fptr *)afs_syscall_stub)->ip;
@@ -259,6 +443,12 @@ int init_module(void)
     sys_call_table32[__NR_afs_syscall] = POINTER2SYSCALL afs_syscall32;
 # endif
 #endif /* AFS_IA64_LINUX20_ENV */
+#ifdef AFS_AMD64_LINUX20_ENV
+    if (ia32_sys_call_table) {
+       ia32_ni_syscall = ia32_sys_call_table[__NR_ia32_afs_syscall];
+       ia32_sys_call_table[__NR_ia32_afs_syscall] = POINTER2SYSCALL afs_syscall;
+    }
+#endif /* AFS_S390_LINUX22_ENV */
 
     osi_Init();
     register_filesystem(&afs_file_system);
@@ -275,18 +465,32 @@ int init_module(void)
 #else /* AFS_IA64_LINUX20_ENV */
     sys_setgroupsp = SYSCALL2POINTER sys_call_table[__NR_setgroups];
     sys_call_table[__NR_setgroups] = POINTER2SYSCALL afs_xsetgroups;
-# ifdef AFS_SPARC64_LINUX20_ENV
+#ifdef AFS_SPARC64_LINUX20_ENV
     sys32_setgroupsp = SYSCALL2POINTER sys_call_table32[__NR_setgroups];
     sys_call_table32[__NR_setgroups] = POINTER2SYSCALL afs32_xsetgroups;
-# endif
-# if defined(__NR_setgroups32)
+#endif /* AFS_SPARC64_LINUX20_ENV */
+#if defined(__NR_setgroups32)
     sys_setgroups32p = SYSCALL2POINTER sys_call_table[__NR_setgroups32];
     sys_call_table[__NR_setgroups32] = POINTER2SYSCALL afs_xsetgroups32;
-# ifdef AFS_SPARC64_LINUX20_ENV
+#ifdef AFS_SPARC64_LINUX20_ENV
     sys32_setgroups32p = SYSCALL2POINTER sys_call_table32[__NR_setgroups32];
     sys_call_table32[__NR_setgroups32] = POINTER2SYSCALL afs32_xsetgroups32;
-# endif
-# endif
+#endif /* AFS_SPARC64_LINUX20_ENV */
+#endif /* __NR_setgroups32 */
+#ifdef AFS_AMD64_LINUX20_ENV 
+    if (ia32_sys_call_table) {
+       sys32_setgroupsp = 
+           SYSCALL2POINTER ia32_sys_call_table[__NR_ia32_setgroups];
+       ia32_sys_call_table[__NR_ia32_setgroups] = 
+           POINTER2SYSCALL afs32_xsetgroups;
+#if defined(__NR_ia32_setgroups32)
+       sys32_setgroups32p = 
+           SYSCALL2POINTER ia32_sys_call_table[__NR_ia32_setgroups32];
+       ia32_sys_call_table[__NR_ia32_setgroups32] = 
+           POINTER2SYSCALL afs32_xsetgroups32;
+#endif /* __NR_ia32_setgroups32 */
+    }
+#endif /* AFS_AMD64_LINUX20_ENV */
 #endif /* AFS_IA64_LINUX20_ENV */
 
     osi_sysctl_init();
@@ -321,6 +525,18 @@ void cleanup_module(void)
 # endif
 # endif
 #endif /* AFS_IA64_LINUX20_ENV */
+#ifdef AFS_AMD64_LINUX20_ENV
+    if (ia32_sys_call_table) {
+       ia32_sys_call_table[__NR_ia32_setgroups] = 
+           POINTER2SYSCALL sys32_setgroupsp;
+       ia32_sys_call_table[__NR_ia32_afs_syscall] = 
+           POINTER2SYSCALL ia32_ni_syscall;
+# if defined(__NR_setgroups32)
+       ia32_sys_call_table[__NR_ia32_setgroups32] = 
+           POINTER2SYSCALL sys32_setgroups32p;
+#endif
+    }
+#endif
     unregister_filesystem(&afs_file_system);
 
     osi_linux_free_inode_pages(); /* Invalidate all pages using AFS inodes. */
@@ -337,16 +553,32 @@ module_exit(afs_cleanup);
 
 static long get_page_offset(void)
 {
-#if defined(AFS_PPC_LINUX22_ENV) || defined(AFS_SPARC64_LINUX20_ENV) || defined(AFS_SPARC_LINUX20_ENV) || defined(AFS_ALPHA_LINUX20_ENV) || defined(AFS_S390_LINUX22_ENV) || defined(AFS_IA64_LINUX20_ENV) || defined(AFS_PARISC_LINUX24_ENV)
+#if defined(AFS_PPC_LINUX22_ENV) || defined(AFS_SPARC64_LINUX20_ENV) || defined(AFS_SPARC_LINUX20_ENV) || defined(AFS_ALPHA_LINUX20_ENV) || defined(AFS_S390_LINUX22_ENV) || defined(AFS_IA64_LINUX20_ENV) || defined(AFS_PARISC_LINUX24_ENV) || defined(AFS_AMD64_LINUX20_ENV)
     return PAGE_OFFSET;
 #else
-    struct task_struct *p;
+    struct task_struct *p, *q;
 
     /* search backward thru the circular list */
-    for(p = current; p; p = p->prev_task)
-       if (p->pid == 1)
-           return p->addr_limit.seg;
-
-    return 0;
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,4,0)
+    read_lock(&tasklist_lock);
+#endif
+    /* search backward thru the circular list */
+#ifdef DEFINED_PREV_TASK
+    for(q = current; p = q; q = prev_task(p)) {
+#else
+    for(p = current; p; p = p->prev_task) {
+#endif
+           if (p->pid == 1) {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,4,0)
+                   read_unlock(&tasklist_lock);
+#endif
+                   return p->addr_limit.seg;
+           }
+    }
+  
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,4,0)
+    read_unlock(&tasklist_lock);
+#endif
+  return 0;
 #endif
 }