Merge patch series "Cleanup some linker list usage issues"

Tom Rini <[email protected]> says:

In looking at some other issues, I saw the comment in include/event.h
about LTO discarding linker lists sometimes. Upon further investigation,
this was a sandbox-specific problem for which this problem was a
symptom. Also, the linker list code has always marked itself as "unused"
and while Marek thinks this might have been due to warnings at the time,
that is no longer the case. This series corrects sandbox to not have an
issue with linker lists in two files, stops marking linker lists as
unused and removes a now obsolete comment.

Link: https://lore.kernel.org/r/[email protected]

2 files changed, 5 insertions, 39 deletions

diff --git a/include/event.h b/include/event.h
index 3ce5f992b04..450281f666a 100644
--- a/include/event.h
+++ b/include/event.h
@@ -308,44 +308,13 @@ static inline const char *event_spy_id(struct evspy_info *spy)
 #endif
 }
 
-/*
- * It seems that LTO will drop list entries if it decides they are not used,
- * although the conditions that cause this are unclear.
- *
- * The example found is the following:
- *
- * static int sandbox_misc_init_f(void *ctx, struct event *event)
- * {
- *    return sandbox_early_getopt_check();
- * }
- * EVENT_SPY_FULL(EVT_MISC_INIT_F, sandbox_misc_init_f);
- *
- * where EVENT_SPY_FULL uses ll_entry_declare()
- *
- * In this case, LTO decides to drop the sandbox_misc_init_f() function
- * (which is fine) but then drops the linker-list entry too. This means
- * that the code no longer works, in this case sandbox no-longer checks its
- * command-line arguments properly.
- *
- * Without LTO, the KEEP() command in the .lds file is enough to keep the
- * entry around. But with LTO it seems that the entry has already been
- * dropped before the link script is considered.
- *
- * The only solution I can think of is to mark linker-list entries as 'used'
- * using an attribute. This should be safe, since we don't actually want to drop
- * any of these. However this does slightly limit LTO's optimisation choices.
- *
- * Another issue has come up, only with clang: using 'static' makes it throw
- * away the linker-list entry sometimes, e.g. with the EVT_FT_FIXUP entry in
- * vbe_simple.c - so for now, make it global.
- */
 #define EVENT_SPY_FULL(_type, _func) \
-	__used ll_entry_declare(struct evspy_info, _type ## _3_ ## _func, \
+	ll_entry_declare(struct evspy_info, _type ## _3_ ## _func, \
 		evspy_info) = _ESPY_REC(_type, _func)
 
 /* Simple spy with no function arguments */
 #define EVENT_SPY_SIMPLE(_type, _func) \
-	__used ll_entry_declare(struct evspy_info_simple, \
+	ll_entry_declare(struct evspy_info_simple, \
 		_type ## _3_ ## _func, \
 		evspy_info) = _ESPY_REC_SIMPLE(_type, _func)
 
diff --git a/include/linker_lists.h b/include/linker_lists.h
index 4425fcb6785..a8b7e2c9f2b 100644
--- a/include/linker_lists.h
+++ b/include/linker_lists.h
@@ -69,7 +69,6 @@
  */
 #define ll_entry_declare(_type, _name, _list)				\
 	_type _u_boot_list_2_##_list##_2_##_name __aligned(4)		\
-			__attribute__((unused))				\
 			__section("__u_boot_list_2_"#_list"_2_"#_name)
 
 /**
@@ -92,7 +91,6 @@
  */
 #define ll_entry_declare_list(_type, _name, _list)			\
 	_type _u_boot_list_2_##_list##_2_##_name[] __aligned(4)		\
-			__attribute__((unused))				\
 			__section("__u_boot_list_2_"#_list"_2_"#_name)
 
 /*
@@ -125,7 +123,6 @@
 #define ll_entry_start(_type, _list)					\
 ({									\
 	static char start[0] __aligned(CONFIG_LINKER_LIST_ALIGN)	\
-		__attribute__((unused))					\
 		__section("__u_boot_list_2_"#_list"_1");			\
 	_type * tmp = (_type *)&start;					\
 	asm("":"+r"(tmp));						\
@@ -167,7 +164,7 @@
  */
 #define ll_entry_end(_type, _list)					\
 ({									\
-	static char end[0] __aligned(1) __attribute__((unused))		\
+	static char end[0] __aligned(1)					\
 		__section("__u_boot_list_2_"#_list"_3");			\
 	_type * tmp = (_type *)&end;					\
 	asm("":"+r"(tmp));						\
@@ -251,7 +248,7 @@
  */
 #define ll_start_decl(_sym, _type, _list)					\
 	static _type _sym[0] __aligned(CONFIG_LINKER_LIST_ALIGN)	\
-		__maybe_unused __section("__u_boot_list_2_" #_list "_1")
+		__section("__u_boot_list_2_" #_list "_1")
 
 /*
  * ll_end_decl uses __aligned(1) to avoid padding before the end marker.
@@ -259,7 +256,7 @@
  */
 #define ll_end_decl(_sym, _type, _list)					\
 	static _type _sym[0] __aligned(1)				\
-		__maybe_unused __section("__u_boot_list_2_" #_list "_3")
+		__section("__u_boot_list_2_" #_list "_3")
 
 /**
  * ll_entry_get() - Retrieve entry from linker-generated array by name