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Subject[RFC v5 11/57] objtool: Abstract alternative special case handling
Date
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.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
---
tools/objtool/arch/x86/Build | 1 +
tools/objtool/arch/x86/arch_special.c | 34 +++++++++++++++++++
tools/objtool/arch/x86/include/arch_special.h | 5 +++
tools/objtool/special.c | 25 +-------------
tools/objtool/special.h | 8 +++++
5 files changed, 49 insertions(+), 24 deletions(-)
create mode 100644 tools/objtool/arch/x86/arch_special.c

diff --git a/tools/objtool/arch/x86/Build b/tools/objtool/arch/x86/Build
index e43fd6fa0ee1..971f9fa90a3c 100644
--- a/tools/objtool/arch/x86/Build
+++ b/tools/objtool/arch/x86/Build
@@ -1,3 +1,4 @@
+objtool-y += arch_special.o
objtool-y += decode.o
objtool-y += orc_dump.o
objtool-y += orc_gen.o
diff --git a/tools/objtool/arch/x86/arch_special.c b/tools/objtool/arch/x86/arch_special.c
new file mode 100644
index 000000000000..6dba31f419d0
--- /dev/null
+++ b/tools/objtool/arch/x86/arch_special.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "../../special.h"
+#include "../../builtin.h"
+
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
+{
+ /*
+ * 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.
+ */
+ switch (feature) {
+ case X86_FEATURE_SMAP:
+ 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/arch/x86/include/arch_special.h b/tools/objtool/arch/x86/include/arch_special.h
index 426178d504a8..3ab2dc32424b 100644
--- a/tools/objtool/arch/x86/include/arch_special.h
+++ b/tools/objtool/arch/x86/include/arch_special.h
@@ -20,4 +20,9 @@
#define X86_FEATURE_POPCNT (4 * 32 + 23)
#define X86_FEATURE_SMAP (9 * 32 + 20)

+struct special_alt;
+
+#define arch_handle_alternative arch_handle_alternative
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt);
+
#endif /* _X86_ARCH_SPECIAL_H */
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index b8ccee1b5382..67461b25e649 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -75,30 +75,7 @@ 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_rela = find_rela_by_dest(sec, offset + entry->orig);
diff --git a/tools/objtool/special.h b/tools/objtool/special.h
index 35061530e46e..738a05bc6d3a 100644
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -8,6 +8,7 @@

#include <stdbool.h>
#include "elf.h"
+#include "arch_special.h"

struct special_alt {
struct list_head list;
@@ -28,4 +29,11 @@ struct special_alt {

int special_get_alts(struct elf *elf, struct list_head *alts);

+#ifndef arch_handle_alternative
+static inline void arch_handle_alternative(unsigned short feature,
+ struct special_alt *alt)
+{
+}
+#endif
+
#endif /* _SPECIAL_H */
--
2.21.0
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