x86: Initialize CPU info via IFUNC relocation [BZ 26203]

Message ID 20200704151859.3317864-1-hjl.tools@gmail.com
State New
Headers show
Series
  • x86: Initialize CPU info via IFUNC relocation [BZ 26203]
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Commit Message

H.J. Lu via Libc-alpha July 4, 2020, 3:18 p.m.
X86 CPU features in ld.so are initialized by init_cpu_features, which is
invoked by DL_PLATFORM_INIT from _dl_sysdep_start.  But when ld.so is
loaded by static executable, DL_PLATFORM_INIT is never called.  Also
x86 cache info in libc.o and libc.a is initialized by a constructor
which may be called too late.  Instead, we should initialize x86 CPU
features and cache info by initializing dummy function pointers via
IFUNC relocation.

Note: _dl_x86_init_cpu_features can be called more than once from
DL_PLATFORM_INIT and during relocation.
---
 sysdeps/i386/dl-machine.h         |  3 +--
 sysdeps/x86/cacheinfo.c           | 10 +++++++++-
 sysdeps/x86/cpu-features.h        |  3 +--
 sysdeps/x86/dl-get-cpu-features.c | 23 ++++++++++++++++++++++-
 sysdeps/x86_64/dl-machine.h       |  3 +--
 5 files changed, 34 insertions(+), 8 deletions(-)

-- 
2.26.2

Patch

diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
index 0f08079e48..5e22e795cc 100644
--- a/sysdeps/i386/dl-machine.h
+++ b/sysdeps/i386/dl-machine.h
@@ -25,7 +25,6 @@ 
 #include <sysdep.h>
 #include <tls.h>
 #include <dl-tlsdesc.h>
-#include <cpu-features.c>
 
 /* Return nonzero iff ELF header is compatible with the running host.  */
 static inline int __attribute__ ((unused))
@@ -250,7 +249,7 @@  dl_platform_init (void)
 #if IS_IN (rtld)
   /* init_cpu_features has been called early from __libc_start_main in
      static executable.  */
-  init_cpu_features (&GLRO(dl_x86_cpu_features));
+  _dl_x86_init_cpu_features ();
 #else
   if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
     /* Avoid an empty string which would disturb us.  */
diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
index 311502dee3..d90126c9fd 100644
--- a/sysdeps/x86/cacheinfo.c
+++ b/sysdeps/x86/cacheinfo.c
@@ -755,7 +755,6 @@  intel_bug_no_cache_info:
 
 
 static void
-__attribute__((constructor))
 init_cacheinfo (void)
 {
   /* Find out what brand of processor.  */
@@ -769,6 +768,8 @@  init_cacheinfo (void)
   unsigned int threads = 0;
   const struct cpu_features *cpu_features = __get_cpu_features ();
 
+  assert (cpu_features->basic.kind != arch_kind_unknown);
+
   if (cpu_features->basic.kind == arch_kind_intel)
     {
       data = handle_intel (_SC_LEVEL1_DCACHE_SIZE, cpu_features);
@@ -874,4 +875,11 @@  init_cacheinfo (void)
        : __x86_shared_cache_size * threads * 3 / 4);
 }
 
+/* NB: Call init_cacheinfo by initializing a dummy function pointer via
+   IFUNC relocation.  */
+extern void __x86_cacheinfo (void) attribute_hidden;
+const void (*__x86_cacheinfo_p) (void) attribute_hidden
+  = __x86_cacheinfo;
+
+__ifunc (__x86_cacheinfo, __x86_cacheinfo, NULL, void, init_cacheinfo);
 #endif
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index d66dc206f7..5ca61b5099 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -844,8 +844,7 @@  extern const struct cpu_features *__get_cpu_features (void)
 /* Unused for x86.  */
 #  define INIT_ARCH()
 #  define __get_cpu_features()	(&GLRO(dl_x86_cpu_features))
-#  define x86_get_cpuid_registers(i) \
-       (&(GLRO(dl_x86_cpu_features).cpuid[i]))
+extern void _dl_x86_init_cpu_features (void) attribute_hidden;
 # endif
 
 #ifdef __x86_64__
diff --git a/sysdeps/x86/dl-get-cpu-features.c b/sysdeps/x86/dl-get-cpu-features.c
index 9d61cd56be..a31c41de5b 100644
--- a/sysdeps/x86/dl-get-cpu-features.c
+++ b/sysdeps/x86/dl-get-cpu-features.c
@@ -1,4 +1,4 @@ 
-/* This file is part of the GNU C Library.
+/* Initialize CPU feature data via IFUNC relocation.
    Copyright (C) 2015-2020 Free Software Foundation, Inc.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -18,6 +18,27 @@ 
 
 #include <ldsodefs.h>
 
+#ifdef SHARED
+# include <cpu-features.c>
+
+/* NB: Call init_cpu_features by initializing a dummy function pointer
+   via IFUNC relocation.  */
+extern void __x86_cpu_features (void) attribute_hidden;
+const void (*__x86_cpu_features_p) (void) attribute_hidden
+  = __x86_cpu_features;
+
+void
+_dl_x86_init_cpu_features (void)
+{
+  struct cpu_features *cpu_features = __get_cpu_features ();
+  if (cpu_features->basic.kind == arch_kind_unknown)
+    init_cpu_features (cpu_features);
+}
+
+__ifunc (__x86_cpu_features, __x86_cpu_features, NULL, void,
+	 _dl_x86_init_cpu_features);
+#endif
+
 #undef __get_cpu_features
 
 const struct cpu_features *
diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index 8e9baffeb4..1105bd7775 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -26,7 +26,6 @@ 
 #include <sysdep.h>
 #include <tls.h>
 #include <dl-tlsdesc.h>
-#include <cpu-features.c>
 
 /* Return nonzero iff ELF header is compatible with the running host.  */
 static inline int __attribute__ ((unused))
@@ -225,7 +224,7 @@  dl_platform_init (void)
 #if IS_IN (rtld)
   /* init_cpu_features has been called early from __libc_start_main in
      static executable.  */
-  init_cpu_features (&GLRO(dl_x86_cpu_features));
+  _dl_x86_init_cpu_features ();
 #else
   if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
     /* Avoid an empty string which would disturb us.  */