[PATCH v2 01/10] linkage: new macros for assembler symbols

Jiri Slaby
2017-03-20T12:32:13Z

Introduce new C macros for annotations of functions and data in
assembly. There is a long-term mess in macros like ENTRY, END, ENDPROC
and similar. They are used in different manners and sometimes
incorrectly.

So introduce macros with clear use to annotate assembly as follows:

a) Support macros
SYM_T_FUNC -- type used by assembler to mark functions
SYM_T_OBJECT -- type used by assembler to mark data

They are defined as STT_FUNC and STT_OBJECT respectively. According
to the gas manual, this is the most portable way. I am not sure about
other assemblers, so we can switch this back to %function and %object
if this turns into a problem. Architectures can also override them by
something like ", @function" if need be.

SYM_A_ALIGN, SYM_A_NOALIGN -- should we align the symbol?
SYM_V_GLOBAL, SYM_V_WEAK, SYM_V_LOCAL -- visibility of symbols
b) Mostly internal annotations, used by the ones below
SYM_START -- use only if you have to
SYM_END -- use only if you have to
c) Generic annotations
d) Annotations for code
SYM_FUNC_START_LOCAL_ALIAS -- use where there are two local names for
one code
SYM_FUNC_START_ALIAS -- use where there are two global names for one
code
SYM_FUNC_END_ALIAS -- the end of LOCAL_ALIASed or ALIASed code

SYM_FUNC_START -- use for global functions
SYM_FUNC_START_LOCAL -- use for local functions
SYM_FUNC_START_WEAK -- use for weak functions
SYM_FUNC_END -- the end of SYM_FUNC_START_LOCAL, SYM_FUNC_START,
SYM_FUNC_START_WEAK, ...

SYM_FUNC_INNER_LABEL -- only for global labels in the middle of
functions
d) For data
SYM_DATA_START -- global data symbol
SYM_DATA_END -- the end of SYM_DATA_START symbol

==========

Note that SYM_FUNC_START_WEAK aligns symbols now too.

The macros allow to pair starts and ends of functions and mark function
correctly in the output ELF objects. This will also help a lot to
generate DWARF information automatically during build of asm.

Finally, all users of the old macros will be converted to use these
later.

[v2]
* use SYM_ prefix and sane names
* add SYM_START and SYM_END and parametrize all the macros

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: hpa@zytor.com
Cc: Ingo Molnar <mingo@kernel.org>
Cc: jpoimboe@redhat.com
Cc: Juergen Gross <jgross@suse.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: mingo@redhat.com
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Cc: x86@kernel.org
---
arch/x86/include/asm/linkage.h | 5 +-
include/linux/linkage.h | 131 ++++++++++++++++++++++++++++++++++++++---
2 files changed, 126 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 0ccb26dda126..a96f6fc36011 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -12,9 +12,8 @@

#ifdef __ASSEMBLY__

-#define GLOBAL(name) \
- .globl name; \
- name:
+/* deprecated, use SYM_DATA_START, SYM_FUNC_START, or SYM_FUNC_INNER_LABEL */
+#define GLOBAL(name) SYM_DATA_START(name)

#if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
#define __ALIGN .p2align 4, 0x90
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index a6a42dd02466..c1dc824d2bc6 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -74,25 +74,46 @@

#ifdef __ASSEMBLY__

+/* SYM_T_FUNC -- type used by assembler to mark functions */
+#ifndef SYM_T_FUNC
+#define SYM_T_FUNC STT_FUNC
+#endif
+
+/* SYM_T_OBJECT -- type used by assembler to mark data */
+#ifndef SYM_T_OBJECT
+#define SYM_T_OBJECT STT_OBJECT
+#endif
+
+/* SYM_A_* -- should we align the symbol? */
+#define SYM_A_ALIGN ALIGN
+#define SYM_A_NOALIGN /* nothing */
+
+/* SYM_V_* -- visibility of symbols */
+#define SYM_V_GLOBAL(name) .globl name
+#define SYM_V_WEAK(name) .weak name
+#define SYM_V_LOCAL(name) /* nothing */
+
#ifndef LINKER_SCRIPT
#define ALIGN __ALIGN
#define ALIGN_STR __ALIGN_STR

+/* === DEPRECATED annotations === */
+
#ifndef ENTRY
+/* deprecated, use SYM_FUNC_START */
#define ENTRY(name) \
- .globl name ASM_NL \
- ALIGN ASM_NL \
- name:
+ SYM_FUNC_START(name)
#endif
#endif /* LINKER_SCRIPT */

#ifndef WEAK
+/* deprecated, use SYM_FUNC_START_WEAK */
#define WEAK(name) \
- .weak name ASM_NL \
- name:
+ SYM_FUNC_START_WEAK(name)
#endif

#ifndef END
+/* deprecated, use SYM_FUNC_END, SYM_DATA_END, or SYM_END */
#define END(name) \
.size name, .-name
#endif
@@ -102,9 +123,105 @@
* static analysis tools such as stack depth analyzer.
*/
#ifndef ENDPROC
+/* deprecated, use SYM_FUNC_END */
#define ENDPROC(name) \
- .type name, @function ASM_NL \
- END(name)
+ SYM_FUNC_END(name)
+#endif
+
+/* === generic annotations === */
+
+/* SYM_START -- use only if you have to */
+#ifndef SYM_START
+#define SYM_START(name, align, visibility) \
+ visibility(name) ASM_NL \
+ align ASM_NL \
+ name:
+#endif
+
+/* SYM_END -- use only if you have to */
+#ifndef SYM_END
+#define SYM_END(name, sym_type) \
+ .type name sym_type ASM_NL \
+ .size name, .-name
+#endif
+
+/* === code annotations === */
+
+/* SYM_FUNC_START_LOCAL_ALIAS -- use where there are two local names for one code */
+#ifndef SYM_FUNC_START_LOCAL_ALIAS
+#define SYM_FUNC_START_LOCAL_ALIAS(name) \
+ SYM_START(name, SYM_A_ALIGN, SYM_V_LOCAL)
+#endif
+
+/* SYM_FUNC_START_ALIAS -- use where there are two global names for one code */
+#ifndef SYM_FUNC_START_ALIAS
+#define SYM_FUNC_START_ALIAS(name) \
+ SYM_START(name, SYM_A_ALIGN, SYM_V_GLOBAL)
+#endif
+
+/* SYM_FUNC_START -- use for global functions */
+#ifndef SYM_FUNC_START
+/*
+ * The same as SYM_FUNC_START_ALIAS, but we will need to distinguish these two
+ * later.
+ */
+#define SYM_FUNC_START(name) \
+ SYM_START(name, SYM_A_ALIGN, SYM_V_GLOBAL)
+#endif
+
+/* SYM_FUNC_START_LOCAL -- use for local functions */
+#ifndef SYM_FUNC_START_LOCAL
+/* the same as SYM_FUNC_START_LOCAL_ALIAS, see comment near SYM_FUNC_START */
+#define SYM_FUNC_START_LOCAL(name) \
+ SYM_START(name, SYM_A_ALIGN, SYM_V_LOCAL)
+#endif
+
+/* SYM_FUNC_START_WEAK -- use for weak functions */
+#ifndef SYM_FUNC_START_WEAK
+#define SYM_FUNC_START_WEAK(name) \
+ SYM_START(name, SYM_A_ALIGN, SYM_V_WEAK)
+#endif
+
+/* SYM_FUNC_END_ALIAS -- the end of LOCAL_ALIASed or ALIASed code */
+#ifndef SYM_FUNC_END_ALIAS
+#define SYM_FUNC_END_ALIAS(name) \
+ SYM_END(name, SYM_T_FUNC)
+#endif
+
+/*
+ * SYM_FUNC_END -- the end of SYM_FUNC_START_LOCAL, SYM_FUNC_START,
+ * SYM_FUNC_START_WEAK, ...
+ */
+#ifndef SYM_FUNC_END
+/* the same as SYM_FUNC_END_ALIAS, see comment near SYM_FUNC_START */
+#define SYM_FUNC_END(name) \
+ SYM_END(name, SYM_T_FUNC)
+#endif
+
+/* SYM_FUNC_INNER_LABEL -- only for global labels to the middle of functions */
+#ifndef SYM_FUNC_INNER_LABEL
+#define SYM_FUNC_INNER_LABEL(name) \
+ SYM_START(name, SYM_A_NOALIGN, SYM_V_GLOBAL)
+#endif
+
+/* === data annotations === */
+
+/* SYM_DATA_START -- global data symbol */
+#ifndef SYM_DATA_START
+#define SYM_DATA_START(name) \
+ SYM_START(name, SYM_A_NOALIGN, SYM_V_GLOBAL)
+#endif
+
+/* SYM_DATA_START -- local data symbol */
+#ifndef SYM_DATA_START_LOCAL
+#define SYM_DATA_START_LOCAL(name) \
+ SYM_START(name, SYM_A_NOALIGN, SYM_V_LOCAL)
+#endif
+
+/* SYM_DATA_END -- the end of SYM_DATA_START symbol */
+#ifndef SYM_DATA_END
+#define SYM_DATA_END(name) \
+ SYM_END(name, SYM_T_OBJECT)
#endif

#endif
--
2.12.0