[RFC 17/22] compiler: Option to default to hidden symbols
From: Thomas Garnier <hidden>
Date: 2017-07-18 22:33:28
Also in:
kvm, linux-arch, linux-crypto, xen-devel
Subsystem:
generic include/asm header files, sparse checker, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Arnd Bergmann, Chris Li, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
Provide an option to default visibility to hidden except for key symbols. This option is disabled by default and will be used by x86_64 PIE support to remove errors between compilation units. Signed-off-by: Thomas Garnier <redacted> --- arch/x86/boot/boot.h | 2 +- arch/x86/include/asm/setup.h | 2 +- include/asm-generic/sections.h | 6 ++++++ include/linux/compiler.h | 8 ++++++++ init/Kconfig | 7 +++++++ kernel/kallsyms.c | 16 ++++++++-------- 6 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index ef5a9cc66fb8..d726c35bdd96 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h@@ -193,7 +193,7 @@ static inline bool memcmp_gs(const void *s1, addr_t s2, size_t len) } /* Heap -- available for dynamic lists. */ -extern char _end[]; +extern char _end[] __default_visibility; extern char *HEAP; extern char *heap_end; #define RESET_HEAP() ((void *)( HEAP = _end ))
diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index e4585a393965..f3ffad82bdc0 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h@@ -66,7 +66,7 @@ static inline void x86_ce4100_early_setup(void) { } * This is set up by the setup-routine at boot-time */ extern struct boot_params boot_params; -extern char _text[]; +extern char _text[] __default_visibility; static inline bool kaslr_enabled(void) {
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 532372c6cf15..27c12f6dd6e2 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h@@ -28,6 +28,9 @@ * __entry_text_start, __entry_text_end * __ctors_start, __ctors_end */ +#ifdef CONFIG_DEFAULT_HIDDEN +#pragma GCC visibility push(default) +#endif extern char _text[], _stext[], _etext[]; extern char _data[], _sdata[], _edata[]; extern char __bss_start[], __bss_stop[];
@@ -42,6 +45,9 @@ extern char __start_rodata[], __end_rodata[]; /* Start and end of .ctors section - used for constructor calls. */ extern char __ctors_start[], __ctors_end[]; +#ifdef CONFIG_DEFAULT_HIDDEN +#pragma GCC visibility pop +#endif extern __visible const void __nosave_begin, __nosave_end;
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index eca8ad75e28b..876b827fe4a7 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h@@ -78,6 +78,14 @@ extern void __chk_io_ptr(const volatile void __iomem *); #include <linux/compiler-clang.h> #endif +/* Useful for Position Independent Code to reduce global references */ +#ifdef CONFIG_DEFAULT_HIDDEN +#pragma GCC visibility push(hidden) +#define __default_visibility __attribute__((visibility ("default"))) +#else +#define __default_visibility +#endif + /* * Generic compiler-dependent macros required for kernel * build go below this comment. Actual compiler/compiler version
diff --git a/init/Kconfig b/init/Kconfig
index 4fb5d6fc2c4f..a93626d40355 100644
--- a/init/Kconfig
+++ b/init/Kconfig@@ -1635,6 +1635,13 @@ config PROFILING config TRACEPOINTS bool +# +# Default to hidden visibility for all symbols. +# Useful for Position Independent Code to reduce global references. +# +config DEFAULT_HIDDEN + bool + source "arch/Kconfig" endmenu # General setup
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 127e7cfafa55..252019c8c3a9 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c@@ -32,24 +32,24 @@ * These will be re-linked against their real values * during the second link stage. */ -extern const unsigned long kallsyms_addresses[] __weak; -extern const int kallsyms_offsets[] __weak; -extern const u8 kallsyms_names[] __weak; +extern const unsigned long kallsyms_addresses[] __weak __default_visibility; +extern const int kallsyms_offsets[] __weak __default_visibility; +extern const u8 kallsyms_names[] __weak __default_visibility; /* * Tell the compiler that the count isn't in the small data section if the arch * has one (eg: FRV). */ extern const unsigned long kallsyms_num_syms -__attribute__((weak, section(".rodata"))); +__attribute__((weak, section(".rodata"))) __default_visibility; extern const unsigned long kallsyms_relative_base -__attribute__((weak, section(".rodata"))); +__attribute__((weak, section(".rodata"))) __default_visibility; -extern const u8 kallsyms_token_table[] __weak; -extern const u16 kallsyms_token_index[] __weak; +extern const u8 kallsyms_token_table[] __weak __default_visibility; +extern const u16 kallsyms_token_index[] __weak __default_visibility; -extern const unsigned long kallsyms_markers[] __weak; +extern const unsigned long kallsyms_markers[] __weak __default_visibility; static inline int is_kernel_inittext(unsigned long addr) {
--
2.13.2.932.g7449e964c-goog
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