[RFC v4 09/18] gcc-plugins: objtool: Add plugin to detect switch table on arm64

[Raphael Gault]

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@xxxxxxx>
---
 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 d33de0b9f4f5..1daeffb55dce 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