[PATCH v3 04/10] objtool: Abstract alternative special case handling

[Julien Thierry]

Some alternatives associated with a specific feature need to be treated
in a special way. Since the features and how to treat them vary from one
architecture to another, move the special case handling to arch specific
code.

Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/x86/Build     |  1 +
 tools/objtool/arch/x86/special.c | 37 ++++++++++++++++++++++++++++++++
 tools/objtool/objtool.h          |  2 ++
 tools/objtool/special.c          | 32 +++++----------------------
 tools/objtool/special.h          |  2 ++
 tools/objtool/weak.c             |  2 --
 6 files changed, 47 insertions(+), 29 deletions(-)
 create mode 100644 tools/objtool/arch/x86/special.c

diff --git a/tools/objtool/arch/x86/Build b/tools/objtool/arch/x86/Build
index 7c5004008e97..9f7869b5c5e0 100644
--- a/tools/objtool/arch/x86/Build
+++ b/tools/objtool/arch/x86/Build
@@ -1,3 +1,4 @@
+objtool-y += special.o
 objtool-y += decode.o
 
 inat_tables_script = ../arch/x86/tools/gen-insn-attr-x86.awk
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
new file mode 100644
index 000000000000..823561e4015c
--- /dev/null
+++ b/tools/objtool/arch/x86/special.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "../../special.h"
+#include "../../builtin.h"
+
+#define X86_FEATURE_POPCNT (4 * 32 + 23)
+#define X86_FEATURE_SMAP   (9 * 32 + 20)
+
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
+{
+	switch (feature) {
+	case X86_FEATURE_SMAP:
+		/*
+		 * If UACCESS validation is enabled; force that alternative;
+		 * otherwise force it the other way.
+		 *
+		 * What we want to avoid is having both the original and the
+		 * alternative code flow at the same time, in that case we can
+		 * find paths that see the STAC but take the NOP instead of
+		 * CLAC and the other way around.
+		 */
+		if (uaccess)
+			alt->skip_orig = true;
+		else
+			alt->skip_alt = true;
+		break;
+	case X86_FEATURE_POPCNT:
+		/*
+		 * It has been requested that we don't validate the !POPCNT
+		 * feature path which is a "very very small percentage of
+		 * machines".
+		 */
+		alt->skip_orig = true;
+		break;
+	default:
+		break;
+	}
+}
diff --git a/tools/objtool/objtool.h b/tools/objtool/objtool.h
index 46240098f08d..79716f4158e8 100644
--- a/tools/objtool/objtool.h
+++ b/tools/objtool/objtool.h
@@ -12,6 +12,8 @@
 
 #include "elf.h"
 
+#define __weak __attribute__((weak))
+
 struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index b04f395de5de..1a2420febd08 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -16,9 +16,6 @@
 #include "warn.h"
 #include "arch_special.h"
 
-#define X86_FEATURE_POPCNT (4*32+23)
-#define X86_FEATURE_SMAP   (9*32+20)
-
 struct special_entry {
 	const char *sec;
 	bool group, jump_or_nop;
@@ -54,6 +51,10 @@ struct special_entry entries[] = {
 	{},
 };
 
+void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)
+{
+}
+
 static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 			 struct section *sec, int idx,
 			 struct special_alt *alt)
@@ -78,30 +79,7 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 
 		feature = *(unsigned short *)(sec->data->d_buf + offset +
 					      entry->feature);
-
-		/*
-		 * It has been requested that we don't validate the !POPCNT
-		 * feature path which is a "very very small percentage of
-		 * machines".
-		 */
-		if (feature == X86_FEATURE_POPCNT)
-			alt->skip_orig = true;
-
-		/*
-		 * If UACCESS validation is enabled; force that alternative;
-		 * otherwise force it the other way.
-		 *
-		 * What we want to avoid is having both the original and the
-		 * alternative code flow at the same time, in that case we can
-		 * find paths that see the STAC but take the NOP instead of
-		 * CLAC and the other way around.
-		 */
-		if (feature == X86_FEATURE_SMAP) {
-			if (uaccess)
-				alt->skip_orig = true;
-			else
-				alt->skip_alt = true;
-		}
+		arch_handle_alternative(feature, alt);
 	}
 
 	orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);
diff --git a/tools/objtool/special.h b/tools/objtool/special.h
index 35061530e46e..44da89afeda2 100644
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -28,4 +28,6 @@ struct special_alt {
 
 int special_get_alts(struct elf *elf, struct list_head *alts);
 
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt);
+
 #endif /* _SPECIAL_H */
diff --git a/tools/objtool/weak.c b/tools/objtool/weak.c
index 29180d599b08..7843e9a7a72f 100644
--- a/tools/objtool/weak.c
+++ b/tools/objtool/weak.c
@@ -9,8 +9,6 @@
 #include <errno.h>
 #include "objtool.h"
 
-#define __weak __attribute__((weak))
-
 #define UNSUPPORTED(name)						\
 ({									\
 	fprintf(stderr, "error: objtool: " name " not implemented\n");	\
-- 
2.21.3