[PATCH 16/24] objtool: Implement jump_assert for _static_cpu_has()

[Peter Zijlstra]

Unlike the jump_label bits, static_cpu_has is implemented with
alternatives. We use the new type field to distinguish them from any
other alternatives

Like jump_labels, make static_cpu_has set static_jump_dest on the
instructions after the static branch such that we can assert on it.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 tools/objtool/check.c   |   21 +++++++++++++++++++++
 tools/objtool/special.c |   26 +++++++++++++++-----------
 tools/objtool/special.h |    1 +
 3 files changed, 37 insertions(+), 11 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -636,6 +636,12 @@ static int handle_group_alt(struct objto
 	fake_jump->ignore = true;
 
 	if (!special_alt->new_len) {
+		/*
+		 * The NOP case for _static_cpu_has()
+		 */
+		if (special_alt->static_cpu_has)
+			fake_jump->jump_dest->static_jump_dest = true;
+
 		*new_insn = fake_jump;
 		return 0;
 	}
@@ -664,6 +670,21 @@ static int handle_group_alt(struct objto
 				  insn->sec, insn->offset);
 			return -1;
 		}
+
+		if (special_alt->static_cpu_has) {
+			if (insn->type != INSN_JUMP_UNCONDITIONAL) {
+				WARN_FUNC("not an unconditional jump in _static_cpu_has()",
+					  insn->sec, insn->offset);
+			}
+			if (insn->jump_dest == fake_jump) {
+				WARN_FUNC("jump inside alternative for _static_cpu_has()",
+					  insn->sec, insn->offset);
+			}
+			/*
+			 * The JMP+disp case for _static_cpu_has()
+			 */
+			insn->jump_dest->static_jump_dest = true;
+		}
 	}
 
 	if (!last_new_insn) {
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -40,6 +40,10 @@
 #define ALT_FEATURE_OFFSET	8
 #define ALT_ORIG_LEN_OFFSET	10
 #define ALT_NEW_LEN_OFFSET	11
+#define ALT_TYPE_OFFSET		13
+
+#define ALT_TYPE_DEFAULT	0
+#define ALT_TYPE_STATIC_CPU_HAS	1
 
 #define X86_FEATURE_POPCNT (4*32+23)
 
@@ -48,7 +52,6 @@ struct special_entry {
 	bool group, jump_or_nop;
 	unsigned char size, orig, new;
 	unsigned char orig_len, new_len; /* group only */
-	unsigned char feature; /* ALTERNATIVE macro CPU feature */
 };
 
 struct special_entry entries[] = {
@@ -60,7 +63,6 @@ struct special_entry entries[] = {
 		.orig_len = ALT_ORIG_LEN_OFFSET,
 		.new = ALT_NEW_OFFSET,
 		.new_len = ALT_NEW_LEN_OFFSET,
-		.feature = ALT_FEATURE_OFFSET,
 	},
 	{
 		.sec = "__jump_table",
@@ -84,24 +86,23 @@ static int get_alt_entry(struct elf *elf
 {
 	struct rela *orig_rela, *new_rela;
 	unsigned long offset;
+	void *data;
 
 	offset = idx * entry->size;
+	data = sec->data->d_buf + offset;
 
 	alt->group = entry->group;
 	alt->jump_or_nop = entry->jump_or_nop;
 
 	if (alt->group) {
-		alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset +
-						   entry->orig_len);
-		alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
-						  entry->new_len);
-	}
-
-	if (entry->feature) {
 		unsigned short feature;
+		unsigned char type;
 
-		feature = *(unsigned short *)(sec->data->d_buf + offset +
-					      entry->feature);
+		alt->orig_len = *(unsigned char *)(data + entry->orig_len);
+		alt->new_len = *(unsigned char *)(data + entry->new_len);
+
+		feature = *(unsigned short *)(data + ALT_FEATURE_OFFSET);
+		type = *(unsigned char *)(data + ALT_TYPE_OFFSET);
 
 		/*
 		 * It has been requested that we don't validate the !POPCNT
@@ -110,6 +111,9 @@ static int get_alt_entry(struct elf *elf
 		 */
 		if (feature == X86_FEATURE_POPCNT)
 			alt->skip_orig = true;
+
+		if (type == ALT_TYPE_STATIC_CPU_HAS)
+			alt->static_cpu_has = true;
 	}
 
 	orig_rela = find_rela_by_dest(sec, offset + entry->orig);
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -27,6 +27,7 @@ struct special_alt {
 	bool group;
 	bool skip_orig;
 	bool jump_or_nop;
+	bool static_cpu_has;
 
 	struct section *orig_sec;
 	unsigned long orig_off;