Linux: Consolidate auxiliary vector parsing (redo)

And optimize it slightly.

This is commit 8c8510ab27 revised.

In _dl_aux_init in elf/dl-support.c, use an explicit loop
and -fno-tree-loop-distribute-patterns to avoid memset.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

elf/Makefile

@@ -160,6 +160,11 @@ ifeq (yes,$(have-loop-to-function))
 CFLAGS-rtld.c += -fno-tree-loop-distribute-patterns
 endif
 
+ifeq (yes,$(have-loop-to-function))
+# Likewise, during static library startup, memset is not yet available.
+CFLAGS-dl-support.c = -fno-tree-loop-distribute-patterns
+endif
+
 # Compile rtld itself without stack protection.
 # Also compile all routines in the static library that are elided from
 # the shared libc because they are in libc.a in the same way.

elf/dl-support.c

@@ -44,6 +44,7 @@
 #include <dl-vdso-setup.h>
 #include <dl-auxv.h>
 #include <dl-find_object.h>
+#include <array_length.h>
 
 extern char *__progname;
 char **_dl_argv = &__progname;	/* This is checked for some error messages.  */
@@ -240,93 +241,25 @@ __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 
 
 #ifdef HAVE_AUX_VECTOR
+#include <dl-parse_auxv.h>
+
 int _dl_clktck;
 
 void
 _dl_aux_init (ElfW(auxv_t) *av)
 {
-  int seen = 0;
-  uid_t uid = 0;
-  gid_t gid = 0;
-
 #ifdef NEED_DL_SYSINFO
   /* NB: Avoid RELATIVE relocation in static PIE.  */
   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 #endif
 
   _dl_auxv = av;
-  for (; av->a_type != AT_NULL; ++av)
-    switch (av->a_type)
-      {
-      case AT_PAGESZ:
-	if (av->a_un.a_val != 0)
-	  GLRO(dl_pagesize) = av->a_un.a_val;
-	break;
-      case AT_CLKTCK:
-	GLRO(dl_clktck) = av->a_un.a_val;
-	break;
-      case AT_PHDR:
-	GL(dl_phdr) = (const void *) av->a_un.a_val;
-	break;
-      case AT_PHNUM:
-	GL(dl_phnum) = av->a_un.a_val;
-	break;
-      case AT_PLATFORM:
-	GLRO(dl_platform) = (void *) av->a_un.a_val;
-	break;
-      case AT_HWCAP:
-	GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
-	break;
-      case AT_HWCAP2:
-	GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
-	break;
-      case AT_FPUCW:
-	GLRO(dl_fpu_control) = av->a_un.a_val;
-	break;
-#ifdef NEED_DL_SYSINFO
-      case AT_SYSINFO:
-	GL(dl_sysinfo) = av->a_un.a_val;
-	break;
-#endif
-#ifdef NEED_DL_SYSINFO_DSO
-      case AT_SYSINFO_EHDR:
-	GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
-	break;
-#endif
-      case AT_UID:
-	uid ^= av->a_un.a_val;
-	seen |= 1;
-	break;
-      case AT_EUID:
-	uid ^= av->a_un.a_val;
-	seen |= 2;
-	break;
-      case AT_GID:
-	gid ^= av->a_un.a_val;
-	seen |= 4;
-	break;
-      case AT_EGID:
-	gid ^= av->a_un.a_val;
-	seen |= 8;
-	break;
-      case AT_SECURE:
-	seen = -1;
-	__libc_enable_secure = av->a_un.a_val;
-	__libc_enable_secure_decided = 1;
-	break;
-      case AT_RANDOM:
-	_dl_random = (void *) av->a_un.a_val;
-	break;
-      case AT_MINSIGSTKSZ:
-	_dl_minsigstacksize = av->a_un.a_val;
-	break;
-      DL_PLATFORM_AUXV
-      }
-  if (seen == 0xf)
-    {
-      __libc_enable_secure = uid != 0 || gid != 0;
-      __libc_enable_secure_decided = 1;
-    }
+  dl_parse_auxv_t auxv_values;
+  /* Use an explicit initialization loop here because memset may not
+     be available yet.  */
+  for (int i = 0; i < array_length (auxv_values); ++i)
+    auxv_values[i] = 0;
+  _dl_parse_auxv (av, auxv_values);
 }
 #endif
 

sysdeps/unix/sysv/linux/alpha/dl-auxv.h

@@ -20,16 +20,8 @@
 
 extern long __libc_alpha_cache_shape[4];
 
-#define DL_PLATFORM_AUXV				\
-      case AT_L1I_CACHESHAPE:				\
-	__libc_alpha_cache_shape[0] = av->a_un.a_val;	\
-	break;						\
-      case AT_L1D_CACHESHAPE:				\
-	__libc_alpha_cache_shape[1] = av->a_un.a_val;	\
-	break;						\
-      case AT_L2_CACHESHAPE:				\
-	__libc_alpha_cache_shape[2] = av->a_un.a_val;	\
-	break;						\
-      case AT_L3_CACHESHAPE:				\
-	__libc_alpha_cache_shape[3] = av->a_un.a_val;	\
-	break;
+#define DL_PLATFORM_AUXV					\
+  __libc_alpha_cache_shape[0] = auxv_values[AT_L1I_CACHESHAPE]; \
+  __libc_alpha_cache_shape[1] = auxv_values[AT_L1D_CACHESHAPE]; \
+  __libc_alpha_cache_shape[2] = auxv_values[AT_L2_CACHESHAPE];	\
+  __libc_alpha_cache_shape[3] = auxv_values[AT_L3_CACHESHAPE];

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

@@ -0,0 +1,61 @@
+/* Parse the Linux auxiliary vector.
+   Copyright (C) 1995-2022 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/>.  */
+
+#include <elf.h>
+#include <entry.h>
+#include <fpu_control.h>
+#include <ldsodefs.h>
+#include <link.h>
+
+typedef ElfW(Addr) dl_parse_auxv_t[AT_MINSIGSTKSZ + 1];
+
+/* Copy the auxiliary vector into AUXV_VALUES and set up GLRO
+   variables.  */
+static inline
+void _dl_parse_auxv (ElfW(auxv_t) *av, dl_parse_auxv_t auxv_values)
+{
+  auxv_values[AT_ENTRY] = (ElfW(Addr)) ENTRY_POINT;
+  auxv_values[AT_PAGESZ] = EXEC_PAGESIZE;
+  auxv_values[AT_FPUCW] = _FPU_DEFAULT;
+
+  /* NB: Default to a constant CONSTANT_MINSIGSTKSZ.  */
+  _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
+                  "CONSTANT_MINSIGSTKSZ is constant");
+  auxv_values[AT_MINSIGSTKSZ] = CONSTANT_MINSIGSTKSZ;
+
+  for (; av->a_type != AT_NULL; av++)
+    if (av->a_type <= AT_MINSIGSTKSZ)
+      auxv_values[av->a_type] = av->a_un.a_val;
+
+  GLRO(dl_pagesize) = auxv_values[AT_PAGESZ];
+  __libc_enable_secure = auxv_values[AT_SECURE];
+  GLRO(dl_platform) = (void *) auxv_values[AT_PLATFORM];
+  GLRO(dl_hwcap) = auxv_values[AT_HWCAP];
+  GLRO(dl_hwcap2) = auxv_values[AT_HWCAP2];
+  GLRO(dl_clktck) = auxv_values[AT_CLKTCK];
+  GLRO(dl_fpu_control) = auxv_values[AT_FPUCW];
+  _dl_random = (void *) auxv_values[AT_RANDOM];
+  GLRO(dl_minsigstacksize) = auxv_values[AT_MINSIGSTKSZ];
+  GLRO(dl_sysinfo_dso) = (void *) auxv_values[AT_SYSINFO_EHDR];
+#ifdef NEED_DL_SYSINFO
+  if (GLRO(dl_sysinfo_dso) != NULL)
+    GLRO(dl_sysinfo) = auxv_values[AT_SYSINFO];
+#endif
+
+  DL_PLATFORM_AUXV
+}

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

@@ -18,15 +18,14 @@
 
 #include <_itoa.h>
 #include <assert.h>
-#include <dl-hwcap-check.h>
+#include <dl-auxv.h>
 #include <dl-osinfo.h>
+#include <dl-parse_auxv.h>
 #include <dl-procinfo.h>
 #include <dl-tunables.h>
 #include <elf.h>
-#include <entry.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <fpu_control.h>
 #include <ldsodefs.h>
 #include <libc-internal.h>
 #include <libintl.h>
@@ -43,10 +42,9 @@
 #include <unistd.h>
 
 #include <dl-machine.h>
+#include <dl-hwcap-check.h>
 
 #ifdef SHARED
-# include <dl-auxv.h>
-
 extern char **_environ attribute_hidden;
 extern char _end[] attribute_hidden;
 
@@ -64,20 +62,20 @@ void *_dl_random attribute_relro = NULL;
 # define DL_STACK_END(cookie) ((void *) (cookie))
 #endif
 
-ElfW(Addr)
-_dl_sysdep_start (void **start_argptr,
-		  void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
-				   ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
+/* Arguments passed to dl_main.  */
+struct dl_main_arguments
 {
-  const ElfW(Phdr) *phdr = NULL;
-  ElfW(Word) phnum = 0;
+  const ElfW(Phdr) *phdr;
+  ElfW(Word) phnum;
   ElfW(Addr) user_entry;
-  ElfW(auxv_t) *av;
-#ifdef NEED_DL_SYSINFO
-  uintptr_t new_sysinfo = 0;
-#endif
+};
 
-  __libc_stack_end = DL_STACK_END (start_argptr);
+/* Separate function, so that dl_main can be called without the large
+   array on the stack.  */
+static void
+_dl_sysdep_parse_arguments (void **start_argptr,
+			    struct dl_main_arguments *args)
+{
   _dl_argc = (intptr_t) *start_argptr;
   _dl_argv = (char **) (start_argptr + 1); /* Necessary aliasing violation.  */
   _environ = _dl_argv + _dl_argc + 1;
@@ -89,74 +87,25 @@ _dl_sysdep_start (void **start_argptr,
 	break;
       }
 
-  user_entry = (ElfW(Addr)) ENTRY_POINT;
-  GLRO(dl_platform) = NULL; /* Default to nothing known about the platform.  */
+  dl_parse_auxv_t auxv_values = { 0, };
+  _dl_parse_auxv (GLRO(dl_auxv), auxv_values);
 
-  /* NB: Default to a constant CONSTANT_MINSIGSTKSZ.  */
-  _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
-		  "CONSTANT_MINSIGSTKSZ is constant");
-  GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;
+  args->phdr = (const ElfW(Phdr) *) auxv_values[AT_PHDR];
+  args->phnum = auxv_values[AT_PHNUM];
+  args->user_entry = auxv_values[AT_ENTRY];
+}
 
-  for (av = GLRO(dl_auxv); av->a_type != AT_NULL; av++)
-    switch (av->a_type)
-      {
-      case AT_PHDR:
-	phdr = (void *) av->a_un.a_val;
-	break;
-      case AT_PHNUM:
-	phnum = av->a_un.a_val;
-	break;
-      case AT_PAGESZ:
-	GLRO(dl_pagesize) = av->a_un.a_val;
-	break;
-      case AT_ENTRY:
-	user_entry = av->a_un.a_val;
-	break;
-      case AT_SECURE:
-	__libc_enable_secure = av->a_un.a_val;
-	break;
-      case AT_PLATFORM:
-	GLRO(dl_platform) = (void *) av->a_un.a_val;
-	break;
-      case AT_HWCAP:
-	GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
-	break;
-      case AT_HWCAP2:
-	GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
-	break;
-      case AT_CLKTCK:
-	GLRO(dl_clktck) = av->a_un.a_val;
-	break;
-      case AT_FPUCW:
-	GLRO(dl_fpu_control) = av->a_un.a_val;
-	break;
-#ifdef NEED_DL_SYSINFO
-      case AT_SYSINFO:
-	new_sysinfo = av->a_un.a_val;
-	break;
-#endif
-      case AT_SYSINFO_EHDR:
-	GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
-	break;
-      case AT_RANDOM:
-	_dl_random = (void *) av->a_un.a_val;
-	break;
-      case AT_MINSIGSTKSZ:
-	GLRO(dl_minsigstacksize) = av->a_un.a_val;
-	break;
-      DL_PLATFORM_AUXV
-      }
+ElfW(Addr)
+_dl_sysdep_start (void **start_argptr,
+		  void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
+				   ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
+{
+  __libc_stack_end = DL_STACK_END (start_argptr);
 
-  dl_hwcap_check ();
+  struct dl_main_arguments dl_main_args;
+  _dl_sysdep_parse_arguments (start_argptr, &dl_main_args);
 
-#ifdef NEED_DL_SYSINFO
-  if (new_sysinfo != 0)
-    {
-      /* Only set the sysinfo value if we also have the vsyscall DSO.  */
-      if (GLRO(dl_sysinfo_dso) != 0)
-        GLRO(dl_sysinfo) = new_sysinfo;
-    }
-#endif
+  dl_hwcap_check ();
 
   __tunables_init (_environ);
 
@@ -188,8 +137,9 @@ _dl_sysdep_start (void **start_argptr,
   if (__builtin_expect (__libc_enable_secure, 0))
     __libc_check_standard_fds ();
 
-  (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
-  return user_entry;
+  (*dl_main) (dl_main_args.phdr, dl_main_args.phnum,
+              &dl_main_args.user_entry, GLRO(dl_auxv));
+  return dl_main_args.user_entry;
 }
 
 void

sysdeps/unix/sysv/linux/powerpc/dl-auxv.h

@@ -16,15 +16,5 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <ldsodefs.h>
-
-#if IS_IN (libc) && !defined SHARED
-int GLRO(dl_cache_line_size);
-#endif
-
-/* Scan the Aux Vector for the "Data Cache Block Size" entry and assign it
-   to dl_cache_line_size.  */
-#define DL_PLATFORM_AUXV						      \
-      case AT_DCACHEBSIZE:						      \
-	GLRO(dl_cache_line_size) = av->a_un.a_val;			      \
-	break;
+#define DL_PLATFORM_AUXV \
+  GLRO(dl_cache_line_size) = auxv_values[AT_DCACHEBSIZE];

sysdeps/unix/sysv/linux/powerpc/dl-support.c

@@ -0,0 +1,4 @@
+#include <elf/dl-support.c>
+
+/* Populated from the auxiliary vector.  */
+int _dl_cache_line_size;