Messages in this thread Patch in this message | | | From | Rasmus Villemoes <> | Subject | [PATCH v3 23/23] x86_64: use relative pointers with dynamic debug | Date | Sat, 10 Nov 2018 00:10:21 +0100 |
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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.
That, however, leads to another problem if the same identifier is used in two different DEFINE_DYNAMIC_DEBUG_METADATA() in the same translation unit: They would both end up referring to the same (first occuring) instance. So the second one would end up using the wrong file, line, function etc. information. All current in-tree macro users of DEFINE_DYNAMIC_DEBUG_METADATA() have been updated to ensure they use UNIQUE_ID to generate the identifier.
To prevent such a problem from going unnoticed, we use a guard symbol in assembly whose value is unique per DEFINE_DYNAMIC_DEBUG_METADATA invocation.
Cc: x86@kernel.org Cc: Ingo Molnar <mingo@kernel.org> Cc: Jason Baron <jbaron@akamai.com> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- arch/x86/Kconfig | 1 + arch/x86/include/asm/dynamic_debug.h | 58 ++++++++++++++++++++++++++++ arch/x86/kernel/macros.S | 1 + 3 files changed, 60 insertions(+) create mode 100644 arch/x86/include/asm/dynamic_debug.h
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index ba7e3464ee92..c7cb31f39e5a 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -91,6 +91,7 @@ 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..80730409183f --- /dev/null +++ b/arch/x86/include/asm/dynamic_debug.h @@ -0,0 +1,58 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_X86_DYNAMIC_DEBUG_H +#define _ASM_X86_DYNAMIC_DEBUG_H + +#ifndef __ASSEMBLY__ + +#ifdef DEBUG +#define _DPRINTK_INIT_TRUE 1 +#else +#define _DPRINTK_INIT_TRUE 0 +#endif + +#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \ + extern struct _ddebug name; \ + asm volatile("DYNAMIC_DEBUG_METADATA" \ + " ident="__stringify(name) \ + " modname=%c0" \ + " func=%c1" \ + " file=%c2" \ + " fmt=%c3" \ + " flag_line=%c4" \ + " init_true=%c5" \ + " cnt=%c6" \ + : : "i" (KBUILD_MODNAME), "i" (__func__), \ + "i" (__FILE__), "i" (fmt), \ + "i" (_DPRINTK_FLAGS_LINENO_INIT), \ + "i" (_DPRINTK_INIT_TRUE), \ + "i" (__COUNTER__) \ + ) + +#else /* __ASSEMBLY__ */ + +.macro DYNAMIC_DEBUG_METADATA ident modname func file fmt flag_line init_true cnt +.ifndef \ident + .pushsection __verbose,"aw" +\ident : + .long \modname - \ident + .long \func - \ident + .long \file - \ident + .long \fmt - \ident + .long \flag_line + .long 0 + .if \init_true + STATIC_KEY_INIT_TRUE + .else + STATIC_KEY_INIT_FALSE + .endif + .popsection + .set \ident\().ddebug.once, \cnt +.elseif \ident\().ddebug.once - \cnt + .error "'\ident' used as _ddebug identifier more than once" +.endif +.endm + +#endif /* __ASSEMBLY__ */ + +#endif /* _ASM_X86_DYNAMIC_DEBUG_H */ + diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S index 161c95059044..2c2b8e5229a9 100644 --- a/arch/x86/kernel/macros.S +++ b/arch/x86/kernel/macros.S @@ -14,3 +14,4 @@ #include <asm/asm.h> #include <asm/cpufeature.h> #include <asm/jump_label.h> +#include <asm/dynamic_debug.h> -- 2.19.1.6.gbde171bbf5
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