[PATCH v2 15/27] compiler: Option to default to hidden symbols
From: Thomas Garnier <hidden>
Date: 2018-03-13 20:59:33
Also in:
kvm, linux-arch, linux-pm, lkml, xen-devel
Subsystem:
driver core, kobjects, debugfs and sysfs, dynamic debug, generic include/asm header files, library code, sparse checker, the rest, tracing, x86 architecture (32-bit and 64-bit), x86 microcode update support · Maintainers:
Greg Kroah-Hartman, "Rafael J. Wysocki", Danilo Krummrich, Jason Baron, Jim Cromie, Arnd Bergmann, Andrew Morton, Chris Li, Linus Torvalds, Steven Rostedt, Masami Hiramatsu, 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. The default visibility is also enabled for external symbols that are compared as they maybe equals (start/end of sections). In this case, older versions of GCC will remove the comparison if the symbols are hidden. This issue exists at least on gcc 4.9 and before. Signed-off-by: Thomas Garnier <redacted> --- arch/x86/boot/boot.h | 2 +- arch/x86/include/asm/setup.h | 2 +- arch/x86/kernel/cpu/microcode/core.c | 4 ++-- drivers/base/firmware_class.c | 4 ++-- include/asm-generic/sections.h | 6 ++++++ include/linux/compiler.h | 7 +++++++ init/Kconfig | 7 +++++++ kernel/kallsyms.c | 16 ++++++++-------- kernel/trace/trace.h | 4 ++-- lib/dynamic_debug.c | 4 ++-- 10 files changed, 38 insertions(+), 18 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 3108e297d87d..dfba64fe1c7e 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h@@ -70,7 +70,7 @@ 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/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index aa1b9a422f2b..ed5675db6e82 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c@@ -141,8 +141,8 @@ static bool __init check_loader_disabled_bsp(void) return *res; } -extern struct builtin_fw __start_builtin_fw[]; -extern struct builtin_fw __end_builtin_fw[]; +extern struct builtin_fw __start_builtin_fw[] __default_visibility; +extern struct builtin_fw __end_builtin_fw[] __default_visibility; bool get_builtin_firmware(struct cpio_data *cd, const char *name) {
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 7dd36ace6152..939a1952d0ab 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c@@ -136,8 +136,8 @@ static struct firmware_cache fw_cache; #ifdef CONFIG_FW_LOADER -extern struct builtin_fw __start_builtin_fw[]; -extern struct builtin_fw __end_builtin_fw[]; +extern struct builtin_fw __start_builtin_fw[] __default_visibility; +extern struct builtin_fw __end_builtin_fw[] __default_visibility; static void fw_copy_to_prealloc_buf(struct firmware *fw, void *buf, size_t size)
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 849cd8eb5ca0..0a0e23405ddd 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h@@ -32,6 +32,9 @@ * __softirqentry_text_start, __softirqentry_text_end * __start_opd, __end_opd */ +#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[];
@@ -49,6 +52,9 @@ extern char __start_once[], __end_once[]; /* 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 /* Start and end of .opd section - used for function descriptors. */ extern char __start_opd[], __end_opd[];
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ab4711c63601..a9ac84e37af9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h@@ -278,6 +278,13 @@ unsigned long read_word_at_a_time(const void *addr) __u.__val; \ }) +#ifdef CONFIG_DEFAULT_HIDDEN +#pragma GCC visibility push(hidden) +#define __default_visibility __attribute__((visibility ("default"))) +#else +#define __default_visibility +#endif + #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */
diff --git a/init/Kconfig b/init/Kconfig
index acc9087546ac..c924babc6d47 100644
--- a/init/Kconfig
+++ b/init/Kconfig@@ -1667,6 +1667,13 @@ 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 a23e21ada81b..f4e58b7a6daf 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c@@ -29,24 +29,24 @@ * 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; /* * Expand a compressed symbol data into the resulting uncompressed string,
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2a6d0325a761..5aebb0dcecba 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h@@ -1741,8 +1741,8 @@ extern int trace_event_enable_disable(struct trace_event_file *file, int enable, int soft_disable); extern int tracing_alloc_snapshot(void); -extern const char *__start___trace_bprintk_fmt[]; -extern const char *__stop___trace_bprintk_fmt[]; +extern const char *__start___trace_bprintk_fmt[] __default_visibility; +extern const char *__stop___trace_bprintk_fmt[] __default_visibility; extern const char *__start___tracepoint_str[]; extern const char *__stop___tracepoint_str[];
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c7c96bc7654a..40b752b53627 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c@@ -37,8 +37,8 @@ #include <linux/device.h> #include <linux/netdevice.h> -extern struct _ddebug __start___verbose[]; -extern struct _ddebug __stop___verbose[]; +extern struct _ddebug __start___verbose[] __default_visibility; +extern struct _ddebug __stop___verbose[] __default_visibility; struct ddebug_table { struct list_head link;
--
2.16.2.660.g709887971b-goog
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel