[RFC v5 43/57] gcc-plugins: objtool: Add plugin to detect switch table on arm64

@@ -90,6 +90,7 @@ config ARM64
 	select DMA_DIRECT_REMAP
 	select EDAC_SUPPORT
 	select FRAME_POINTER
+	select GCC_PLUGIN_SWITCH_TABLES if STACK_VALIDATION
 	select GENERIC_ALLOCATOR
 	select GENERIC_ARCH_TOPOLOGY
 	select GENERIC_CLOCKEVENTS

@@ -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))

@@ -112,4 +112,8 @@ config GCC_PLUGIN_ARM_SSP_PER_TASK
 	bool
 	depends on GCC_PLUGINS && ARM

+config GCC_PLUGIN_SWITCH_TABLES
+	bool
+	depends on GCC_PLUGINS && ARM64
+
 endif

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include "gcc-common.h"
+
+__visible int plugin_is_GPL_compatible;
+
+#define GEN_QUAD(rtx)	assemble_integer_with_op(".quad ", rtx)
+
+/*
+ * Create an array of metadata for each jump table found in the rtl.
+ * The metadata contains:
+ * - A pointer to the table of offsets used for the actual branch
+ * - A pointer to first instruction of the group getting expanded into an
+ *   acutal jump
+ * - The number of entries in the table of offsets
+ * - Whether the offsets in the table are signed or not
+ */
+static unsigned int arm64_switchtbl_rtl_execute(void)
+{
+	rtx_insn *insn;
+	rtx_insn *labelp = NULL;
+	rtx_jump_table_data *tablep = NULL;
+	section *swt_sec;
+	section *curr_sec = current_function_section();
+
+	swt_sec = get_section(".discard.switch_table_info",
+			      SECTION_EXCLUDE | SECTION_COMMON, NULL);
+
+	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) {
+			rtx_code_label *label_to_jump;
+
+			/*
+			 * GCC is a bit touchy about adding the label right
+			 * before the jump rtx_insn as it modifies the
+			 * basic_block created for the jump table.
+			 * Make sure we create the label before the whole
+			 * basic_block of the jump table.
+			 */
+			label_to_jump = gen_label_rtx();
+			SET_LABEL_KIND(label_to_jump, LABEL_NORMAL);
+			emit_label_before(label_to_jump, insn);
+			/* Force label to be kept, apparently LABEL_PRESERVE_P is an rvalue :) */
+			LABEL_PRESERVE_P(label_to_jump) = 1;
+
+			switch_to_section(swt_sec);
+			GEN_QUAD(gen_rtx_LABEL_REF(Pmode, labelp));
+			GEN_QUAD(gen_rtx_LABEL_REF(Pmode, label_to_jump));
+			GEN_QUAD(GEN_INT(GET_NUM_ELEM(tablep->get_labels())));
+			GEN_QUAD(GEN_INT(ADDR_DIFF_VEC_FLAGS(tablep).offset_unsigned));
+			switch_to_section(curr_sec);
+
+			/*
+			 * Scheduler isn't very happy about leaving labels in
+			 * the middle of jump table basic blocks.
+			 */
+			delete_insn(label_to_jump);
+		}
+	}
+	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, "expand", 1,
+		  PASS_POS_INSERT_AFTER);
+
+	register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP,
+			  NULL, &arm64_switchtbl_rtl_pass_info);
+
+	return 0;
+}
--