[PATCH 20/24] objtool: Another static block fail

[Peter Zijlstra]

I've observed GCC generate:

  sym:
     NOP/JMP 1f	(static_branch)
     JMP 2f
  1: /* crud */
     JMP 3f
  2: /* other crud */

  3: RETQ


This means we need to follow unconditional jumps; be conservative and
only follow if its a unique jump.

(I've not yet figured out which CONFIG option is responsible for this,
 a normal defconfig build does not generate crap like this)

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 tools/objtool/check.c |   53 +++++++++++++++++++++++++++++++++++++++++++++++---
 tools/objtool/elf.h   |    2 -
 2 files changed, 51 insertions(+), 4 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1207,6 +1207,8 @@ static int assert_static_jumps(struct ob
 	return 0;
 }
 
+static void jmp_grow_static_block(struct objtool_file *file, struct instruction *insn);
+
 static bool __grow_static_block(struct objtool_file *file,
 				struct instruction *insn)
 {
@@ -1216,7 +1218,8 @@ static bool __grow_static_block(struct o
 
 	switch (insn->type) {
 	case INSN_JUMP_UNCONDITIONAL:
-		/* mark this instruction, terminate this section */
+		/* follow the jump, mark this instruction, terminate this section */
+		jmp_grow_static_block(file, insn);
 		insn->static_jump_dest = true;
 		return false;
 
@@ -1238,6 +1241,50 @@ static bool __grow_static_block(struct o
 	return true;
 }
 
+static void jmp_grow_static_block(struct objtool_file *file, struct instruction *insn)
+{
+	struct instruction *dest = insn->jump_dest;
+	bool old_sjd, static_block;
+
+	if (!dest)
+		return;
+
+	/* more than a single site jumps here, can't be certain */
+	if (dest->branch_target > 1)
+		return;
+
+	/* mark the destination, so we can continue there */
+	old_sjd = dest->static_jump_dest;
+	dest->static_jump_dest = true;
+
+	if (dest->offset > insn->offset) {
+		/* fwd jump, the main iteration will still get there. */
+		return;
+	}
+
+	/* backwards jump, we need to revisit the instructions */
+	do {
+		static_block = __grow_static_block(file, dest);
+
+		if (insn->type == INSN_CALL && !old_sjd && dest->static_jump_dest) {
+			struct symbol *func = insn->call_dest;
+			if (!func || func->bind != STB_LOCAL)
+				goto next;
+
+			/*
+			 * we flipped the call to static, update the stats.
+			 */
+			if (insn->static_jump_dest) {
+				func->non_static_call--;
+				func->static_call++;
+			}
+		}
+next:
+		dest = list_next_entry(dest, list);
+		old_sjd = dest->static_jump_dest;
+	} while (static_block && dest != insn);
+}
+
 static int grow_static_blocks(struct objtool_file *file)
 {
 	bool static_block = false;
@@ -1255,9 +1302,9 @@ static int grow_static_blocks(struct obj
 				continue;
 
 			if (static_block)
-				func->static_call = true;
+				func->static_call++;
 			else
-				func->non_static_call = true;
+				func->non_static_call++;
 		}
 	}
 
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -61,7 +61,7 @@ struct symbol {
 	unsigned char bind, type;
 	unsigned long offset;
 	unsigned int len;
-	bool static_call, non_static_call;
+	unsigned int static_call, non_static_call;
 };
 
 struct rela {