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Subject[RFC V3 09/18] gcc-plugins: objtool: Add plugin to detect switch table on arm64
Date
This plugins comes into play before the final 2 RTL passes of GCC and
detects switch-tables that are to be outputed in the ELF and writes
information in an "objtool_data" section which will be used by objtool.

Signed-off-by: Raphael Gault <raphael.gault@arm.com>
---
scripts/Makefile.gcc-plugins | 2 +
scripts/gcc-plugins/Kconfig | 9 +++
.../arm64_switch_table_detection_plugin.c | 58 +++++++++++++++++++
3 files changed, 69 insertions(+)
create mode 100644 scripts/gcc-plugins/arm64_switch_table_detection_plugin.c

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 5f7df50cfe7a..a56736df9dc2 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -44,6 +44,8 @@ ifdef CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK
endif
export DISABLE_ARM_SSP_PER_TASK_PLUGIN

+gcc-plugin-$(CONFIG_GCC_PLUGIN_SWITCH_TABLES) += arm64_switch_table_detection_plugin.so
+
# All the plugin CFLAGS are collected here in case a build target needs to
# filter them out of the KBUILD_CFLAGS.
GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
index e9c677a53c74..a9b13d257cd2 100644
--- a/scripts/gcc-plugins/Kconfig
+++ b/scripts/gcc-plugins/Kconfig
@@ -113,4 +113,13 @@ config GCC_PLUGIN_ARM_SSP_PER_TASK
bool
depends on GCC_PLUGINS && ARM

+config GCC_PLUGIN_SWITCH_TABLES
+ bool "GCC Plugin: Identify switch tables at compile time"
+ default y
+ depends on STACK_VALIDATION && ARM64
+ help
+ Plugin to identify switch tables generated at compile time and store
+ them in a .objtool_data section. Objtool will then use that section
+ to analyse the different execution path of the switch table.
+
endmenu
diff --git a/scripts/gcc-plugins/arm64_switch_table_detection_plugin.c b/scripts/gcc-plugins/arm64_switch_table_detection_plugin.c
new file mode 100644
index 000000000000..d7f0e13910d5
--- /dev/null
+++ b/scripts/gcc-plugins/arm64_switch_table_detection_plugin.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include "gcc-common.h"
+
+__visible int plugin_is_GPL_compatible;
+
+static unsigned int arm64_switchtbl_rtl_execute(void)
+{
+ rtx_insn *insn;
+ rtx_insn *labelp = NULL;
+ rtx_jump_table_data *tablep = NULL;
+ section *sec = get_section(".objtool_data", SECTION_STRINGS, NULL);
+ section *curr_sec = current_function_section();
+
+ for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) {
+ /*
+ * Find a tablejump_p INSN (using a dispatch table)
+ */
+ if (!tablejump_p(insn, &labelp, &tablep))
+ continue;
+
+ if (labelp && tablep) {
+ switch_to_section(sec);
+ assemble_integer_with_op(".quad ", gen_rtx_LABEL_REF(Pmode, labelp));
+ assemble_integer_with_op(".quad ", GEN_INT(GET_NUM_ELEM(tablep->get_labels())));
+ assemble_integer_with_op(".quad ", GEN_INT(ADDR_DIFF_VEC_FLAGS(tablep).offset_unsigned));
+ switch_to_section(curr_sec);
+ }
+ }
+ return 0;
+}
+
+#define PASS_NAME arm64_switchtbl_rtl
+
+#define NO_GATE
+#include "gcc-generate-rtl-pass.h"
+
+__visible int plugin_init(struct plugin_name_args *plugin_info,
+ struct plugin_gcc_version *version)
+{
+ const char * const plugin_name = plugin_info->base_name;
+ int tso = 0;
+ int i;
+
+ if (!plugin_default_version_check(version, &gcc_version)) {
+ error(G_("incompatible gcc/plugin versions"));
+ return 1;
+ }
+
+ PASS_INFO(arm64_switchtbl_rtl, "outof_cfglayout", 1,
+ PASS_POS_INSERT_AFTER);
+
+ register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP,
+ NULL, &arm64_switchtbl_rtl_pass_info);
+
+ return 0;
+}
--
2.17.1
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