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Subject[PATCH v2 22/23] x86_64: use relative pointers with dynamic debug
Date
Similar to how x86_64 uses bug_entry-relative pointers to reduce
sizeof(struct bug_entry), the same thing can now be done for struct
_ddebug, saving 16 bytes for each of those (i.e., each pr_debug, dev_dbg
etc. in a CONFIG_DYNAMIC_DEBUG kernel).

Note the use of .ifndef/.endif in asm to avoid

fs/aio.c:1382: Error: symbol `__UNIQUE_ID_ddebug112' is already defined

This is due to uses of pr_debug et al in functions that get inlined. In
such a case, __COUNTER__ is obviously only expanded once, but the asm()
is repeated once for every inlined instance. Letting all instances share
the same descriptor object is the right thing to do; that is also what
happens when it is the compiler that defines a static object inside an
inline(d) function.

Cc: x86@kernel.org
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/dynamic_debug.h | 35 ++++++++++++++++++++++++++++
2 files changed, 36 insertions(+)
create mode 100644 arch/x86/include/asm/dynamic_debug.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1a0be022f91d..a44168930e52 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -90,6 +90,7 @@ config X86
select CLOCKSOURCE_WATCHDOG
select DCACHE_WORD_ACCESS
select DMA_DIRECT_OPS
+ select DYNAMIC_DEBUG_RELATIVE_POINTERS if X86_64
select EDAC_ATOMIC_SCRUB
select EDAC_SUPPORT
select GENERIC_CLOCKEVENTS
diff --git a/arch/x86/include/asm/dynamic_debug.h b/arch/x86/include/asm/dynamic_debug.h
new file mode 100644
index 000000000000..350ef6e2feff
--- /dev/null
+++ b/arch/x86/include/asm/dynamic_debug.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_DYNAMIC_DEBUG_H
+#define _ASM_X86_DYNAMIC_DEBUG_H
+
+#ifdef HAVE_JUMP_LABEL
+# ifdef DEBUG
+# define _DPRINTK_ASM_KEY_INIT ASM_STATIC_KEY_INIT_TRUE
+# else
+# define _DPRINTK_ASM_KEY_INIT ASM_STATIC_KEY_INIT_FALSE
+# endif
+#else
+# define _DPRINTK_ASM_KEY_INIT ""
+#endif
+
+#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
+ extern struct _ddebug name; \
+ asm volatile(".ifndef " __stringify(name) "\n" \
+ ".pushsection __verbose,\"aw\"\n" \
+ "1:\n" \
+ __stringify(name) ":\n" \
+ "\t.long %c0 - 1b \t# _ddebug::modname_disp\n" \
+ "\t.long %c1 - 1b \t# _ddebug::function_disp\n" \
+ "\t.long %c2 - 1b \t# _ddebug::filename_disp\n" \
+ "\t.long %c3 - 1b \t# _ddebug::format_disp\n" \
+ "\t.long %c4 \t# _ddebug::flags_lineno\n" \
+ "\t.long 0 \t# <padding>\n" \
+ _DPRINTK_ASM_KEY_INIT \
+ ".popsection\n" \
+ ".endif\n" \
+ : : "i" (KBUILD_MODNAME), "i" (__func__), \
+ "i" (__FILE__), "i" (fmt), \
+ "i" (_DPRINTK_FLAGS_LINENO_INIT))
+
+#endif /* _ASM_X86_DYNAMIC_DEBUG_H */
+
--
2.19.1.3.g1d92a00e68
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