Remove kernel version check

The kernel version check is used to avoid glibc to run on older
kernels where some syscall are not available and fallback code are
not enabled to handle graciously fail.  However, it does not prevent
if the kernel does not correctly advertise its version through
vDSO note, uname or procfs.

Also kernel version checks are sometime not desirable by users,
where they want to deploy on different system with different kernel
version knowing the minimum set of syscall is always presented on
such systems.

The kernel version check has been removed along with the
LD_ASSUME_KERNEL environment variable.  The minimum kernel used to
built glibc is still provided through NT_GNU_ABI_TAG ELF note and
also printed when libc.so is issued.

Checked on x86_64-linux-gnu.

NEWS

@@ -22,6 +22,11 @@ Deprecated and removed features, and other changes affecting compatibility:
   removal of the LD_TRACE_PRELINKING, and LD_USE_LOAD_BIAS, environment
   variables and their functionality in the dynamic loader.
 
+* The Linux kernel version check has been removed along with the
+  LD_ASSUME_KERNEL environment variable.  The minimum kernel used to built
+  glibc is still provided through NT_GNU_ABI_TAG ELF note and also printed
+  when libc.so is issued directly.
+
 Changes to build and runtime requirements:
 
   [Add changes to build and runtime requirements here]

config.h.in

@@ -135,6 +135,9 @@
 /* Linux specific: minimum supported kernel version.  */
 #undef	__LINUX_KERNEL_VERSION
 
+/* Linux specific: __LINUX_KERNEL_VERSION as a string.  */
+#undef  __LINUX_KERNEL_VERSION_STR
+
 /* Override abi-tags ABI version if necessary.  */
 #undef  __ABI_TAG_VERSION
 

csu/libc-start.c

@@ -313,14 +313,6 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
   __stack_chk_guard = stack_chk_guard;
 # endif
 
-# ifdef DL_SYSDEP_OSCHECK
-  {
-    /* This needs to run to initiliaze _dl_osversion before TLS
-       setup might check it.  */
-    DL_SYSDEP_OSCHECK (__libc_fatal);
-  }
-# endif
-
   /* Initialize libpthread if linked in.  */
   if (__pthread_initialize_minimal != NULL)
     __pthread_initialize_minimal ();

csu/version.c

@@ -33,6 +33,9 @@ Compiled by GNU CC version "__VERSION__".\n"
 #ifdef LIBC_ABIS_STRING
 LIBC_ABIS_STRING
 #endif
+#ifdef __LINUX_KERNEL_VERSION_STR
+"Minimum supported kernel: " __LINUX_KERNEL_VERSION_STR "\n"
+#endif
 "For bug reporting instructions, please see:\n\
 "REPORT_BUGS_TO".\n";
 

elf/dl-cache.c

@@ -297,9 +297,6 @@ search_cache (const char *string_table, uint32_t string_table_size,
 
 		      if ((libnew->hwcap & hwcap_exclude) && !named_hwcap)
 			continue;
-		      if (GLRO (dl_osversion)
-			  && libnew->osversion > GLRO (dl_osversion))
-			continue;
 		      if (_DL_PLATFORMS_COUNT
 			  && (libnew->hwcap & _DL_HWCAP_PLATFORM) != 0
 			  && ((libnew->hwcap & _DL_HWCAP_PLATFORM)

elf/dl-diagnostics.c

@@ -231,10 +231,6 @@ print_version (void)
 void
 _dl_print_diagnostics (char **environ)
 {
-#ifdef HAVE_DL_DISCOVER_OSVERSION
-  _dl_diagnostics_print_labeled_value
-    ("dl_discover_osversion", _dl_discover_osversion ());
-#endif
   _dl_diagnostics_print_labeled_string ("dl_dst_lib", DL_DST_LIB);
   _dl_diagnostics_print_labeled_value ("dl_hwcap", GLRO (dl_hwcap));
   _dl_diagnostics_print_labeled_value ("dl_hwcap_important", HWCAP_IMPORTANT);
@@ -243,7 +239,6 @@ _dl_print_diagnostics (char **environ)
     ("dl_hwcaps_subdirs", _dl_hwcaps_subdirs);
   _dl_diagnostics_print_labeled_value
     ("dl_hwcaps_subdirs_active", _dl_hwcaps_subdirs_active ());
-  _dl_diagnostics_print_labeled_value ("dl_osversion", GLRO (dl_osversion));
   _dl_diagnostics_print_labeled_value ("dl_pagesize", GLRO (dl_pagesize));
   _dl_diagnostics_print_labeled_string ("dl_platform", GLRO (dl_platform));
   _dl_diagnostics_print_labeled_string

elf/dl-load.c

@@ -1591,13 +1591,6 @@ open_verify (const char *name, int fd,
     [EI_OSABI] = ELFOSABI_SYSV,
     [EI_ABIVERSION] = 0
   };
-  static const struct
-  {
-    ElfW(Word) vendorlen;
-    ElfW(Word) datalen;
-    ElfW(Word) type;
-    char vendor[4];
-  } expected_note = { 4, 16, 1, "GNU" };
   /* Initialize it to make the compiler happy.  */
   const char *errstring = NULL;
   int errval = 0;
@@ -1628,10 +1621,7 @@ open_verify (const char *name, int fd,
   if (fd != -1)
     {
       ElfW(Ehdr) *ehdr;
-      ElfW(Phdr) *phdr, *ph;
+      ElfW(Phdr) *phdr;
-      ElfW(Word) *abi_note;
-      ElfW(Word) *abi_note_malloced = NULL;
-      unsigned int osversion;
       size_t maplength;
 
       /* We successfully opened the file.  Now verify it is a file
@@ -1695,13 +1685,16 @@ open_verify (const char *name, int fd,
 #endif
 	      )
 	    errstring = N_("invalid ELF header");
+
 	  else if (ehdr->e_ident[EI_CLASS] != ELFW(CLASS))
 	    {
 	      /* This is not a fatal error.  On architectures where
 		 32-bit and 64-bit binaries can be run this might
 		 happen.  */
 	      *found_other_class = true;
-	      goto close_and_out;
+	      __close_nocancel (fd);
+	      __set_errno (ENOENT);
+	      return -1;
 	    }
 	  else if (ehdr->e_ident[EI_DATA] != byteorder)
 	    {
@@ -1736,7 +1729,11 @@ open_verify (const char *name, int fd,
 	  goto lose;
 	}
       if (! __glibc_likely (elf_machine_matches_host (ehdr)))
-	goto close_and_out;
+	{
+	  __close_nocancel (fd);
+	  __set_errno (ENOENT);
+	  return -1;
+	}
       else if (__glibc_unlikely (ehdr->e_type != ET_DYN
 				 && ehdr->e_type != ET_EXEC))
 	{
@@ -1758,7 +1755,6 @@ open_verify (const char *name, int fd,
 	  if ((size_t) __pread64_nocancel (fd, (void *) phdr, maplength,
 					   ehdr->e_phoff) != maplength)
 	    {
-	    read_error:
 	      errval = errno;
 	      errstring = N_("cannot read file data");
 	      goto lose;
@@ -1768,73 +1764,12 @@ open_verify (const char *name, int fd,
       if (__glibc_unlikely (elf_machine_reject_phdr_p
 			    (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
 			     loader, fd)))
-	goto close_and_out;
+	{
+	  __close_nocancel (fd);
+	  __set_errno (ENOENT);
+	  return -1;
+	}
 
-      /* Check .note.ABI-tag if present.  */
-      for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
-	if (ph->p_type == PT_NOTE && ph->p_filesz >= 32
-	    && (ph->p_align == 4 || ph->p_align == 8))
-	  {
-	    ElfW(Addr) size = ph->p_filesz;
-
-	    if (ph->p_offset + size <= (size_t) fbp->len)
-	      abi_note = (void *) (fbp->buf + ph->p_offset);
-	    else
-	      {
-		/* Note: __libc_use_alloca is not usable here, because
-		   thread info may not have been set up yet.  */
-		if (size < __MAX_ALLOCA_CUTOFF)
-		  abi_note = alloca (size);
-		else
-		  {
-		    /* There could be multiple PT_NOTEs.  */
-		    abi_note_malloced = realloc (abi_note_malloced, size);
-		    if (abi_note_malloced == NULL)
-		      goto read_error;
-
-		    abi_note = abi_note_malloced;
-		  }
-		if (__pread64_nocancel (fd, (void *) abi_note, size,
-					ph->p_offset) != size)
-		  {
-		    free (abi_note_malloced);
-		    goto read_error;
-		  }
-	      }
-
-	    while (memcmp (abi_note, &expected_note, sizeof (expected_note)))
-	      {
-		ElfW(Addr) note_size
-		  = ELF_NOTE_NEXT_OFFSET (abi_note[0], abi_note[1],
-					  ph->p_align);
-
-		if (size - 32 < note_size)
-		  {
-		    size = 0;
-		    break;
-		  }
-		size -= note_size;
-		abi_note = (void *) abi_note + note_size;
-	      }
-
-	    if (size == 0)
-	      continue;
-
-	    osversion = (abi_note[5] & 0xff) * 65536
-			+ (abi_note[6] & 0xff) * 256
-			+ (abi_note[7] & 0xff);
-	    if (abi_note[4] != __ABI_TAG_OS
-		|| (GLRO(dl_osversion) && GLRO(dl_osversion) < osversion))
-	      {
-	      close_and_out:
-		__close_nocancel (fd);
-		__set_errno (ENOENT);
-		fd = -1;
-	      }
-
-	    break;
-	  }
-      free (abi_note_malloced);
     }
 
   return fd;

elf/dl-support.c

@@ -145,8 +145,6 @@ size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 
 int _dl_inhibit_cache;
 
-unsigned int _dl_osversion;
-
 /* All known directories in sorted order.  */
 struct r_search_path_elem *_dl_all_dirs;
 
@@ -327,10 +325,6 @@ _dl_non_dynamic_init (void)
   DL_PLATFORM_INIT;
 #endif
 
-#ifdef DL_OSVERSION_INIT
-  DL_OSVERSION_INIT;
-#endif
-
   /* Now determine the length of the platform string.  */
   if (_dl_platform != NULL)
     _dl_platformlen = strlen (_dl_platform);

elf/rtld.c

@@ -384,9 +384,6 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_error_free = _dl_error_free,
     ._dl_tls_get_addr_soft = _dl_tls_get_addr_soft,
     ._dl_libc_freeres = __rtld_libc_freeres,
-#ifdef HAVE_DL_DISCOVER_OSVERSION
-    ._dl_discover_osversion = _dl_discover_osversion
-#endif
   };
 /* If we would use strong_alias here the compiler would see a
    non-hidden definition.  This would undo the effect of the previous
@@ -1710,10 +1707,6 @@ dl_main (const ElfW(Phdr) *phdr,
   /* With vDSO setup we can initialize the function pointers.  */
   setup_vdso_pointers ();
 
-#ifdef DL_SYSDEP_OSCHECK
-  DL_SYSDEP_OSCHECK (_dl_fatal_printf);
-#endif
-
   /* Initialize the data structures for the search paths for shared
      objects.  */
   call_init_paths (&state);
@@ -2638,14 +2631,6 @@ process_envvars (struct dl_main_state *state)
 	    GLRO(dl_dynamic_weak) = 1;
 	  break;
 
-	case 13:
-	  /* We might have some extra environment variable with length 13
-	     to handle.  */
-#ifdef EXTRA_LD_ENVVARS_13
-	  EXTRA_LD_ENVVARS_13
-#endif
-	  break;
-
 	case 14:
 	  /* Where to place the profiling data file.  */
 	  if (!__libc_enable_secure

sysdeps/generic/ldsodefs.h

@@ -552,8 +552,6 @@ struct rtld_global_ro
 /* These two are used only internally.  */
 #define DL_DEBUG_HELP       (1 << 10)
 
-  /* OS version.  */
-  EXTERN unsigned int _dl_osversion;
   /* Platform name.  */
   EXTERN const char *_dl_platform;
   EXTERN size_t _dl_platformlen;
@@ -701,10 +699,6 @@ struct rtld_global_ro
      dlopen.  */
   int (*_dl_find_object) (void *, struct dl_find_object *);
 
-#ifdef HAVE_DL_DISCOVER_OSVERSION
-  int (*_dl_discover_osversion) (void);
-#endif
-
   /* Dynamic linker operations used after static dlopen.  */
   const struct dlfcn_hook *_dl_dlfcn_hook;
 

sysdeps/unix/sysv/linux/configure

@@ -70,6 +70,7 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for kernel header at least $minimum_kernel" >&5
 $as_echo_n "checking for kernel header at least $minimum_kernel... " >&6; }
 decnum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/(\1 * 65536 + \2 * 256 + \3)/'`;
+abinumstr=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1.\2.\3/'`;
 abinum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -96,6 +97,10 @@ $as_echo "$libc_minimum_kernel" >&6; }
 if test "$libc_minimum_kernel" = ok; then
   cat >>confdefs.h <<_ACEOF
 #define __LINUX_KERNEL_VERSION $decnum
+_ACEOF
+
+  cat >>confdefs.h <<_ACEOF
+#define __LINUX_KERNEL_VERSION_STR "$abinumstr"
 _ACEOF
 
   cat >>confdefs.h <<_ACEOF

sysdeps/unix/sysv/linux/configure.ac

@@ -50,6 +50,7 @@ fi
 AC_MSG_CHECKING(for kernel header at least $minimum_kernel)
 changequote(,)dnl
 decnum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/(\1 * 65536 + \2 * 256 + \3)/'`;
+abinumstr=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1.\2.\3/'`;
 abinum=`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1,\2,\3/'`;
 changequote([,])dnl
 AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[#include <linux/version.h>
@@ -59,6 +60,7 @@ AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[#include <linux/version.h>
 AC_MSG_RESULT($libc_minimum_kernel)
 if test "$libc_minimum_kernel" = ok; then
   AC_DEFINE_UNQUOTED(__LINUX_KERNEL_VERSION, $decnum)
+  AC_DEFINE_UNQUOTED(__LINUX_KERNEL_VERSION_STR, "$abinumstr")
   AC_DEFINE_UNQUOTED(__ABI_TAG_VERSION, $abinum)
 else
   AC_MSG_ERROR([*** The available kernel headers are older than the requested

sysdeps/unix/sysv/linux/dl-librecon.h

@@ -1,59 +0,0 @@
-/* Optional code to distinguish library flavours.
-   Copyright (C) 2001-2022 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <https://www.gnu.org/licenses/>.  */
-
-#ifndef _DL_LIBRECON_H
-#define _DL_LIBRECON_H	1
-
-static inline void __attribute__ ((unused, always_inline))
-_dl_osversion_init (char *assume_kernel)
-{
-  unsigned long int i, j, osversion = 0;
-  char *p = assume_kernel, *q;
-
-  for (i = 0; i < 3; i++, p = q + 1)
-    {
-      j = _dl_strtoul (p, &q);
-      if (j >= 255 || p == q || (i < 2 && *q && *q != '.'))
-	{
-	  osversion = 0;
-	  break;
-	}
-      osversion |= j << (16 - 8 * i);
-      if (!*q)
-	break;
-    }
-  if (osversion)
-    GLRO(dl_osversion) = osversion;
-}
-
-/* Recognizing extra environment variables.  */
-#define EXTRA_LD_ENVVARS_13 \
-    if (memcmp (envline, "ASSUME_KERNEL", 13) == 0)			      \
-      {									      \
-	_dl_osversion_init (&envline[14]);				      \
-	break;								      \
-      }
-
-#define DL_OSVERSION_INIT \
-  do {									      \
-    char *assume_kernel = getenv ("LD_ASSUME_KERNEL");			      \
-    if (assume_kernel)							      \
-      _dl_osversion_init (assume_kernel);				      \
-  } while (0)
-
-#endif /* dl-librecon.h */

sysdeps/unix/sysv/linux/dl-osinfo.h

@@ -22,31 +22,6 @@
 #include <stdint.h>
 #include <not-cancel.h>
 
-#ifndef MIN
-# define MIN(a,b) (((a)<(b))?(a):(b))
-#endif
-
-#define DL_SYSDEP_OSCHECK(FATAL)					      \
-  do {									      \
-    /* Test whether the kernel is new enough.  This test is only performed    \
-       if the library is not compiled to run on all kernels.  */	      \
-									      \
-    int version = _dl_discover_osversion ();				      \
-    if (__glibc_likely (version >= 0))					      \
-      {									      \
-	if (__builtin_expect (GLRO(dl_osversion) == 0, 1)		      \
-	    || GLRO(dl_osversion) > version)				      \
-	  GLRO(dl_osversion) = version;					      \
-									      \
-	/* Now we can test with the required version.  */		      \
-	if (__LINUX_KERNEL_VERSION > 0 && version < __LINUX_KERNEL_VERSION)   \
-	  /* Not sufficent.  */						      \
-	  FATAL ("FATAL: kernel too old\n");				      \
-      }									      \
-    else if (__LINUX_KERNEL_VERSION > 0)				      \
-      FATAL ("FATAL: cannot determine kernel version\n");		      \
-  } while (0)
-
 static inline uintptr_t __attribute__ ((always_inline))
 _dl_setup_stack_chk_guard (void *dl_random)
 {

sysdeps/unix/sysv/linux/dl-sysdep.c

@@ -250,96 +250,3 @@ _dl_show_auxv (void)
 }
 
 #endif /* SHARED */
-
-
-int
-attribute_hidden
-_dl_discover_osversion (void)
-{
-#ifdef SHARED
-  if (GLRO(dl_sysinfo_map) != NULL)
-    {
-      /* If the kernel-supplied DSO contains a note indicating the kernel's
-	 version, we don't need to call uname or parse any strings.  */
-
-      static const struct
-      {
-	ElfW(Nhdr) hdr;
-	char vendor[8];
-      } expected_note = { { sizeof "Linux", sizeof (ElfW(Word)), 0 }, "Linux" };
-      const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
-      const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
-      for (unsigned int i = 0; i < phnum; ++i)
-	if (phdr[i].p_type == PT_NOTE)
-	  {
-	    const ElfW(Addr) start = (phdr[i].p_vaddr
-				      + GLRO(dl_sysinfo_map)->l_addr);
-	    const ElfW(Nhdr) *note = (const void *) start;
-	    while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
-	      {
-		if (!memcmp (note, &expected_note, sizeof expected_note))
-		  return *(const ElfW(Word) *) ((const void *) note
-						+ sizeof expected_note);
-#define ROUND(len) (((len) + sizeof note->n_type - 1) & -sizeof note->n_type)
-		note = ((const void *) (note + 1)
-			+ ROUND (note->n_namesz) + ROUND (note->n_descsz));
-#undef ROUND
-	      }
-	  }
-    }
-#endif /* SHARED */
-
-  char bufmem[64];
-  char *buf = bufmem;
-  unsigned int version;
-  int parts;
-  char *cp;
-  struct utsname uts;
-
-  /* Try the uname system call.  */
-  if (__uname (&uts))
-    {
-      /* This was not successful.  Now try reading the /proc filesystem.  */
-      int fd = __open64_nocancel ("/proc/sys/kernel/osrelease", O_RDONLY);
-      if (fd < 0)
-	return -1;
-      ssize_t reslen = __read_nocancel (fd, bufmem, sizeof (bufmem));
-      __close_nocancel (fd);
-      if (reslen <= 0)
-	/* This also didn't work.  We give up since we cannot
-	   make sure the library can actually work.  */
-	return -1;
-      buf[MIN (reslen, (ssize_t) sizeof (bufmem) - 1)] = '\0';
-    }
-  else
-    buf = uts.release;
-
-  /* Now convert it into a number.  The string consists of at most
-     three parts.  */
-  version = 0;
-  parts = 0;
-  cp = buf;
-  while ((*cp >= '0') && (*cp <= '9'))
-    {
-      unsigned int here = *cp++ - '0';
-
-      while ((*cp >= '0') && (*cp <= '9'))
-	{
-	  here *= 10;
-	  here += *cp++ - '0';
-	}
-
-      ++parts;
-      version <<= 8;
-      version |= here;
-
-      if (*cp++ != '.' || parts == 3)
-	/* Another part following?  */
-	break;
-    }
-
-  if (parts < 3)
-    version <<= 8 * (3 - parts);
-
-  return version;
-}

sysdeps/unix/sysv/linux/dl-sysdep.h

@@ -24,10 +24,3 @@
    we aren't making direct use of it.  So enable this across the board.  */
 
 #define NEED_DL_SYSINFO_DSO	1
-
-
-#ifndef __ASSEMBLER__
-/* Get version of the OS.  */
-extern int _dl_discover_osversion (void) attribute_hidden;
-# define HAVE_DL_DISCOVER_OSVERSION	1
-#endif

sysdeps/unix/sysv/linux/i386/dl-librecon.h

@@ -18,8 +18,6 @@
 
 #ifndef _DL_LIBRECON_H
 
-#include <sysdeps/unix/sysv/linux/dl-librecon.h>
-
 #define DISTINGUISH_LIB_VERSIONS \
   do									      \
     {									      \