[PATCH 1/4] x86: Initialize CPU info via IFUNC relocation [BZ 26203]
H.J. Lu
hjl.tools@gmail.com
Fri Sep 18 16:07:06 GMT 2020
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. Since _rtld_global_ro in ld.so is
initialized by dynamic relocation, we can also initialize x86 CPU
features in _rtld_global_ro in ld.so and cache info in libc.so by
initializing dummy function pointers in ld.so and libc.so via IFUNC
relocation.
Note: _dl_x86_init_cpu_features can be called more than once from
DL_PLATFORM_INIT and during relocation in ld.so.
---
sysdeps/i386/dl-machine.h | 3 +--
sysdeps/x86/cacheinfo.c | 10 +++++++++-
sysdeps/x86/dl-get-cpu-features.c | 25 ++++++++++++++++++++++++-
sysdeps/x86/include/cpu-features.h | 1 +
sysdeps/x86_64/dl-machine.h | 3 +--
5 files changed, 36 insertions(+), 6 deletions(-)
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 217c21c34f..7a325ab70e 100644
--- a/sysdeps/x86/cacheinfo.c
+++ b/sysdeps/x86/cacheinfo.c
@@ -756,7 +756,6 @@ intel_bug_no_cache_info:
static void
-__attribute__((constructor))
init_cacheinfo (void)
{
/* Find out what brand of processor. */
@@ -770,6 +769,8 @@ 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);
@@ -894,4 +895,11 @@ init_cacheinfo (void)
# endif
}
+/* 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/dl-get-cpu-features.c b/sysdeps/x86/dl-get-cpu-features.c
index 5f9e46b0c6..da4697b895 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 +18,29 @@
#include <ldsodefs.h>
+#ifdef SHARED
+# include <cpu-features.c>
+
+/* NB: Normally, DL_PLATFORM_INIT calls init_cpu_features to initialize
+ CPU features. But when loading ld.so inside of static executable,
+ DL_PLATFORM_INIT isn't called. Call init_cpu_features by initializing
+ a dummy function pointer via IFUNC relocation for ld.so. */
+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 __x86_get_cpu_features
const struct cpu_features *
diff --git a/sysdeps/x86/include/cpu-features.h b/sysdeps/x86/include/cpu-features.h
index dcf29b6fe8..f62be0b9b3 100644
--- a/sysdeps/x86/include/cpu-features.h
+++ b/sysdeps/x86/include/cpu-features.h
@@ -159,6 +159,7 @@ struct cpu_features
/* Unused for x86. */
# define INIT_ARCH()
# define __x86_get_cpu_features(max) (&GLRO(dl_x86_cpu_features))
+extern void _dl_x86_init_cpu_features (void) attribute_hidden;
# endif
# ifdef __x86_64__
diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index ca73d8fef9..773e94c8bb 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. */
--
2.26.2
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