linux-kernel - [RFC PATCH v4 19/19] dyndbg: RFC add linker rules to module.lds.h

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Message-Id: <20210317065412.2890414-20-jim.cromie@gmail.com>
Date:   Wed, 17 Mar 2021 00:54:12 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Cc:     Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH v4 19/19] dyndbg: RFC add linker rules to module.lds.h

Copy the DYNAMIC_DEBUG_DATA macro, that works in vmlinux.lds.h,
into module.lds.h  This does not work here

The point of the KEEPS is to pack section pairs into consecutive
memory, a property we need in order to drop the _ddebug.site pointer.

The problem (ISTM) is that for linking vmlinux, the data is linked
into .data (and the sections are subsumed), and it is is accessed by
iterating beteween __(fstart|stop)___dyndbg(_sites)? symbols.  That
breaks down here cuz kernel/module.c specifically grabs the __dyndb*
sections by name.

I lack the linker-fu to sort this, so I left my commented out
attempts, to show my errors.

no-bisect: expect linker error
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/asm-generic/module.lds.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/asm-generic/module.lds.h b/include/asm-generic/module.lds.h
index f210d5c1b78b..0074c5f2421b 100644
--- a/include/asm-generic/module.lds.h
+++ b/include/asm-generic/module.lds.h
@@ -7,4 +7,25 @@
  * Empty for the asm-generic header.
  */
 
+/* implement dynamic printk debug section packing */
+#if defined(CONFIG_DYNAMIC_DEBUG) ||					\
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE)				\
+	 && defined(DYNAMIC_DEBUG_MODULE))
+#define DYNAMIC_DEBUG_DATA()						\
+	. = ALIGN(8);							\
+	KEEP(*(__dyndbg_sites .gnu.linkonce.dyndbg_site))		\
+	KEEP(*(__dyndbg .gnu.linkonce.dyndbg))
+#else
+#define DYNAMIC_DEBUG_DATA()
+#endif
+
+SECTIONS {
+__dyndbg	: { (*(__dyndbg .gnu.linkonce.dyndbg)) }
+__dyndbg_sites	: { (*(__dyndbg_sites .gnu.linkonce.dyndbg_site)) }
+
+	//.data.dyndbg : { DYNAMIC_DEBUG_DATA() } // syntax ok
+	//: { DYNAMIC_DEBUG_DATA() }
+	//DYNAMIC_DEBUG_DATA()
+}
+
 #endif /* __ASM_GENERIC_MODULE_LDS_H */
-- 
2.29.2