linux-kernel - [PATCH v6 54/57] dyndbg: add .gnu.linkonce. & _

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Message-Id: <20220904214134.408619-55-jim.cromie@gmail.com>
Date:   Sun,  4 Sep 2022 15:41:31 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     daniel.vetter@...ll.ch, seanpaul@...omium.org, robdclark@...il.com,
        linux@...musvillemoes.dk, joe@...ches.com,
        Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH v6 54/57] dyndbg: add .gnu.linkonce. & __dyndbg* sections in module.lds.h

For a long time now, loadable modules have tacitly linked the __dyndbg
section into the .ko, as is observable in dmesg by enabling module.c's
pr_debugs and loading a module.  Recently, __dyndbg_sites was added,
following the original model.

But now, we need to explicitly name those (__dyndbg, __dyndbg_sites)
sections in order to place new .gnu.linkonce.dyndbg* sections in front
of them.

This gives us the properties we need for _ddebug_map_site() to drop
the _ddebug.site pointer:

   fixed offset from &__dyndbg[N] to &__dyndbg[0]
   container_of gets &header
   header has ptr to __dyndbg_sites[]
   __dyndbg_sites[_map] gives de-duplicated site recs

NOTE

HEAD~1 took headers off front of descs,sites and saved them into
_ddebug_info, this puts the gnu.linkonce.* records into those vectors.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/asm-generic/module.lds.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/module.lds.h b/include/asm-generic/module.lds.h
index f210d5c1b78b..328c48dfc88c 100644
--- a/include/asm-generic/module.lds.h
+++ b/include/asm-generic/module.lds.h
@@ -4,7 +4,17 @@
 
 /*
  * <asm/module.lds.h> can specify arch-specific sections for linking modules.
- * Empty for the asm-generic header.
+ *
+ * For loadable modules with CONFIG_DYNAMIC_DEBUG, we need to keep the
+ * 2 __dyndbg* ELF sections, which are loaded by module.c
+ *
+ * Pack the 2 __dyndbg* input sections with their respective
+ * .gnu.linkonce. header records into 2 output sections, with those
+ * header records in the 0th element.
  */
+SECTIONS {
+__dyndbg_sites	: ALIGN(8) { *(.gnu.linkonce.dyndbg_site) *(__dyndbg_sites) }
+__dyndbg	: ALIGN(8) { *(.gnu.linkonce.dyndbg)	  *(__dyndbg) }
+}
 
 #endif /* __ASM_GENERIC_MODULE_LDS_H */
-- 
2.37.2