Re: [PATCH v5 15/27] compiler: Option to default to hidden symbols
On 06/25/18 15:39, Thomas Garnier wrote: > 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 > --- > diff --git a/init/Kconfig b/init/Kconfig > index 24b60536e26b..d4f90cc38ede 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1718,6 +1718,13 @@ 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 > + I certainly would appreciate a better/more descriptive kconfig symbol name here. > source "arch/Kconfig" > > endmenu # General setup thanks, -- ~Randy
Re: [PATCH v5 15/27] compiler: Option to default to hidden symbols
On 06/25/18 15:39, Thomas Garnier wrote: > 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 > --- > diff --git a/init/Kconfig b/init/Kconfig > index 24b60536e26b..d4f90cc38ede 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1718,6 +1718,13 @@ 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 > + I certainly would appreciate a better/more descriptive kconfig symbol name here. > source "arch/Kconfig" > > endmenu # General setup thanks, -- ~Randy
[PATCH v5 15/27] compiler: Option to default to hidden symbols
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
---
arch/x86/boot/boot.h | 2 +-
arch/x86/include/asm/setup.h | 2 +-
arch/x86/kernel/cpu/microcode/core.c | 4 ++--
drivers/base/firmware_loader/main.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 ae13bc974416..083a6e99b884 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -68,7 +68,7 @@ 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 08286269fd24..3ed2f9d54abb 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -149,8 +149,8 @@ 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_loader/main.c
b/drivers/base/firmware_loader/main.c
index 0943e7065e0e..2ffd019af2d4 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -94,8 +94,8 @@ 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 42506e4d1f53..d9837a58906e 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 24b60536e26b..d4f90cc38ede 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1718,6 +1718,13 @@ 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"
[PATCH v5 15/27] compiler: Option to default to hidden symbols
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
---
arch/x86/boot/boot.h | 2 +-
arch/x86/include/asm/setup.h | 2 +-
arch/x86/kernel/cpu/microcode/core.c | 4 ++--
drivers/base/firmware_loader/main.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 ae13bc974416..083a6e99b884 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -68,7 +68,7 @@ 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 08286269fd24..3ed2f9d54abb 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -149,8 +149,8 @@ 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_loader/main.c
b/drivers/base/firmware_loader/main.c
index 0943e7065e0e..2ffd019af2d4 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -94,8 +94,8 @@ 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 42506e4d1f53..d9837a58906e 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 24b60536e26b..d4f90cc38ede 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1718,6 +1718,13 @@ 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"
