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SubjectRe: [PATCH 22/22] x86_64: use relative pointers with dynamic debug

* Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:

> 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
> 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 */
> +

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

Ingo

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