Hi Raphaël,
On 16/08/19 13:23, Raphael Gault wrote:
This patch abstracts the few architecture dependent tests that are
perform when handling special section and switch tables. It enables any
architecture to ignore a particular CPU feature or not to handle switch
tables.
I think it would be better if this patch only focused on CPU features
and leave dealing with switch table to subsequent patches.
Signed-off-by: Raphael Gault <[email protected]>
---
tools/objtool/arch/arm64/Build | 1 +
tools/objtool/arch/arm64/arch_special.c | 22 +++++++++++++++
.../objtool/arch/arm64/include/arch_special.h | 10 +++++--
tools/objtool/arch/x86/Build | 1 +
tools/objtool/arch/x86/arch_special.c | 28 +++++++++++++++++++
tools/objtool/arch/x86/include/arch_special.h | 9 ++++++
tools/objtool/check.c | 24 ++++++++++++++--
tools/objtool/special.c | 9 ++----
tools/objtool/special.h | 3 ++
9 files changed, 96 insertions(+), 11 deletions(-)
create mode 100644 tools/objtool/arch/arm64/arch_special.c
create mode 100644 tools/objtool/arch/x86/arch_special.c
diff --git a/tools/objtool/arch/arm64/Build b/tools/objtool/arch/arm64/Build
index bf7a32c2b9e9..3d09be745a84 100644
--- a/tools/objtool/arch/arm64/Build
+++ b/tools/objtool/arch/arm64/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/arm64/arch_special.c
b/tools/objtool/arch/arm64/arch_special.c
new file mode 100644
index 000000000000..a21d28876317
--- /dev/null
+++ b/tools/objtool/arch/arm64/arch_special.c
@@ -0,0 +1,22 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#include "../../special.h"
+#include "arch_special.h"
+
+void arch_force_alt_path(unsigned short feature,
+ bool uaccess,
+ struct special_alt *alt)
+{
+}
diff --git a/tools/objtool/arch/arm64/include/arch_special.h
b/tools/objtool/arch/arm64/include/arch_special.h
index 63da775d0581..185103be8a51 100644
--- a/tools/objtool/arch/arm64/include/arch_special.h
+++ b/tools/objtool/arch/arm64/include/arch_special.h
@@ -30,7 +30,13 @@
#define ALT_ORIG_LEN_OFFSET 10
#define ALT_NEW_LEN_OFFSET 11
-#define X86_FEATURE_POPCNT (4 * 32 + 23)
-#define X86_FEATURE_SMAP (9 * 32 + 20)
+static inline bool arch_should_ignore_feature(unsigned short feature)
+{
+ return false;
+}
+static inline bool arch_support_switch_table(void)
+{
+ return false;
If I understand correctly , this gets later (patch 8) replaced by
arch_find_switch_table() which can return NULL if unable to find a
switch table.
So, is it necessary to introduce this function at this stage of the
patchset? Can't we just have directly arch_find_switch_table() ?
Also, I believe that in the end you keep the two
arch_support_switch_table() implementations (x86 and arm64) despite
getting rid of the only caller (in patch 8).
+}
#endif /* _ARM64_ARCH_SPECIAL_H */
diff --git a/tools/objtool/arch/x86/Build b/tools/objtool/arch/x86/Build
index 1f11b45999d0..63e167775bc8 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..6583a1770bb2
--- /dev/null
+++ b/tools/objtool/arch/x86/arch_special.c
@@ -0,0 +1,28 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#include "../../special.h"
+#include "arch_special.h"
+
+void arch_force_alt_path(unsigned short feature,
+ bool uaccess,
Maybe you could have something like:
void arch_select_alt_path(unsigned short feature, struct special_alt *alt);
or arch_process_alt_inst(...);
This way you just let the arch decide what to do for alternative
instructions associated with their features, and call it in the "if
(entry->feature)" branch of get_alt_entry().
You don't need to pass the "uaccess" as that info is globally accessible
from builtin.h.
+ struct special_alt *alt)
+{
+ if (feature == X86_FEATURE_SMAP) {
+ if (uaccess)
+ alt->skip_orig = true;
+ else
+ alt->skip_alt = true;
+ }
+}
diff --git a/tools/objtool/arch/x86/include/arch_special.h
b/tools/objtool/arch/x86/include/arch_special.h
index 424ce47013e3..fce2b1193194 100644
--- a/tools/objtool/arch/x86/include/arch_special.h
+++ b/tools/objtool/arch/x86/include/arch_special.h
@@ -33,4 +33,13 @@
#define X86_FEATURE_POPCNT (4 * 32 + 23)
#define X86_FEATURE_SMAP (9 * 32 + 20)
+static inline bool arch_should_ignore_feature(unsigned short feature)
+{
+ return feature == X86_FEATURE_POPCNT;
+}
With my above suggestion you shouldn't need that and just use the arch
specific alternative handling set the alt->skip_orig.
+
+static inline bool arch_support_switch_table(void)
+{
+ return true;
+}
#endif /* _X86_ARCH_SPECIAL_H */
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 30e147391dcb..4af6422d3428 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -729,7 +729,7 @@ static int handle_group_alt(struct objtool_file *file,
last_orig_insn = insn;
}
- if (next_insn_same_sec(file, last_orig_insn)) {
+ if (last_orig_insn && next_insn_same_sec(file, last_orig_insn)) {
fake_jump = malloc(sizeof(*fake_jump));
if (!fake_jump) {
WARN("malloc failed");
@@ -1061,6 +1061,26 @@ static struct rela *find_jump_table(struct objtool_file
*file,
table_rela = find_rela_by_dest(table_sec, table_offset);
if (!table_rela)
continue;
+ /*
+ * If we are on arm64 architecture, we now that we
+ * are in presence of a switch table thanks to
+ * the `br <Xn>` insn. but we can't retrieve it yet.
+ * So we just ignore unreachable for this file.
+ */
+ if (!arch_support_switch_table()) {
+ file->ignore_unreachables = true;
+ return NULL;
+ }
+
+ rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
+ if (rodata_rela) {
+ /*
+ * Use of RIP-relative switch jumps is quite rare, and
+ * indicates a rare GCC quirk/bug which can leave dead
+ * code behind.
+ */
+ if (text_rela->type == R_X86_64_PC32)
+ file->ignore_unreachables = true;
/*
* Use of RIP-relative switch jumps is quite rare, and
@@ -1864,7 +1884,7 @@ static int validate_branch(struct objtool_file *file,
struct symbol *func,
insn = first;
sec = insn->sec;
- if (insn->alt_group && list_empty(&insn->alts)) {
+ if (!insn->visited && insn->alt_group && list_empty(&insn->alts)) {
WARN_FUNC("don't know how to handle branch to middle of alternative
instruction group",
sec, insn->offset);
return 1;
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index b8ccee1b5382..7a0092d6e5b3 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -81,7 +81,7 @@ static int get_alt_entry(struct elf *elf, struct
special_entry *entry,
* feature path which is a "very very small percentage of
* machines".
*/
- if (feature == X86_FEATURE_POPCNT)
+ if (arch_should_ignore_feature(feature))
alt->skip_orig = true;
/*
@@ -93,12 +93,7 @@ static int get_alt_entry(struct elf *elf, struct
special_entry *entry,
* 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_force_alt_path(feature, uaccess, 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..90626a7e41cf 100644
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -27,5 +27,8 @@ struct special_alt {
};
int special_get_alts(struct elf *elf, struct list_head *alts);
+void arch_force_alt_path(unsigned short feature,
+ bool uaccess,
+ struct special_alt *alt);
#endif /* _SPECIAL_H */
CHeers,
--
Julien Thierry
