debug: symtab: fix linking issue due to variable redefinition

Employs the same linkonce magic of sw_isr_table to fix the
multiple definition of the symtab variables issue that I
get in my application build that doesn't use `west`.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>

cmake/linker_script/common/common-rom.cmake

@@ -188,6 +188,11 @@ zephyr_iterable_section(NAME tracing_backend KVMA RAM_REGION GROUP RODATA_REGION
 zephyr_linker_section(NAME zephyr_dbg_info KVMA RAM_REGION GROUP RODATA_REGION NOINPUT ${XIP_ALIGN_WITH_INPUT})
 zephyr_linker_section_configure(SECTION zephyr_dbg_info INPUT ".zephyr_dbg_info" KEEP)
 
+if(CONFIG_SYMTAB)
+  zephyr_linker_section(NAME symtab KVMA FLASH GROUP RODATA_REGION SUBALIGN 4 NOINPUT)
+  zephyr_linker_section_configure(SECTION symtab INPUT ".gnu.linkonce.symtab*")
+endif()
+
 if (CONFIG_DEVICE_DEPS)
   zephyr_linker_section(NAME device_deps KVMA RAM_REGION GROUP RODATA_REGION NOINPUT ${XIP_ALIGN_WITH_INPUT} ENDALIGN 16)
   zephyr_linker_section_configure(SECTION device_deps INPUT .__device_deps_pass1* KEEP SORT NAME PASS LINKER_DEVICE_DEPS_PASS1)

include/zephyr/linker/common-rom/common-rom-debug.ld

@@ -8,3 +8,10 @@
 	{
 		KEEP(*(".dbg_thread_info"));
 	} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+
+#ifdef CONFIG_SYMTAB
+	SECTION_PROLOGUE(symtab,,)
+	{
+		KEEP(*(_SYMTAB_SECTION_SYMS))
+	} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+#endif /* CONFIG_SYMTAB */

include/zephyr/linker/section_tags.h

@@ -103,6 +103,12 @@
 #define __isr
 #endif
 
+/* Symbol table section */
+#if defined(CONFIG_SYMTAB)
+#define __symtab_info		Z_GENERIC_SECTION(_SYMTAB_INFO_SECTION_NAME)
+#define __symtab_entry		Z_GENERIC_SECTION(_SYMTAB_ENTRY_SECTION_NAME)
+#endif /* CONFIG_SYMTAB */
+
 #endif /* !_ASMLANGUAGE */
 
 #endif /* ZEPHYR_INCLUDE_LINKER_SECTION_TAGS_H_ */

include/zephyr/linker/sections.h

@@ -77,6 +77,13 @@
 #define _NOCACHE_SECTION_NAME nocache
 #endif
 
+/* Symbol table section */
+#if defined(CONFIG_SYMTAB)
+#define _SYMTAB_INFO_SECTION_NAME	.gnu.linkonce.symtab.info
+#define _SYMTAB_ENTRY_SECTION_NAME	.gnu.linkonce.symtab.entry
+#define _SYMTAB_SECTION_SYMS		.gnu.linkonce.symtab*
+#endif /* CONFIG_SYMTAB */
+
 #if defined(CONFIG_LINKER_USE_BOOT_SECTION)
 #define BOOT_TEXT_SECTION_NAME		boot_text
 #define BOOT_BSS_SECTION_NAME		boot_bss

scripts/build/gen_symtab.py

@@ -125,10 +125,11 @@ def main():
     with open(args.output, 'w') as wf:
         print("/* AUTO-GENERATED by gen_symtab.py, do not edit! */", file=wf)
         print("", file=wf)
+        print("#include <zephyr/linker/sections.h>", file=wf)
         print("#include <zephyr/debug/symtab.h>", file=wf)
         print("", file=wf)
         print(
-            f"const struct z_symtab_entry z_symtab_entries[{len(symtab_list) + 1}] = {{", file=wf)
+            f"const struct z_symtab_entry __symtab_entry z_symtab_entries[{len(symtab_list) + 1}] = {{", file=wf)
         for i, entry in enumerate(symtab_list):
             print(
                 f"\t/* ADDR: {hex(entry.addr)} SIZE: {hex(entry.size)} */", file=wf)
@@ -145,7 +146,7 @@ def main():
             f"\t[{len(symtab_list)}] = {{.offset = {dummy_offset}, .name = \"?\"}},", file=wf)
         print(f"}};\n", file=wf)
 
-        print(f"const struct symtab_info z_symtab = {{", file=wf)
+        print(f"const struct symtab_info __symtab_info z_symtab = {{", file=wf)
         print(f"\t.first_addr = {hex(first_addr)},", file=wf)
         print(f"\t.length = {len(symtab_list)},", file=wf)
         print(f"\t.entries = z_symtab_entries,", file=wf)

subsys/debug/symtab/CMakeLists.txt

@@ -1,7 +1,13 @@
+# Copyright (c) 2024 Meta Platforms
 # SPDX-License-Identifier: Apache-2.0
 
-add_library(symtab
+zephyr_library()
+
+zephyr_library_sources(
   symtab.c
+)
+
+add_library(symtab
   symtab_stub.c
 )
 

subsys/debug/symtab/symtab_stub.c

@@ -4,11 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <zephyr/linker/sections.h>
 #include <zephyr/debug/symtab.h>
 
 /**
  * These are placeholder variables. They will be replaced by the real ones
  * generated by `gen_symtab.py`.
  */
-const struct z_symtab_entry *z_symtab_entries;
-const struct symtab_info z_symtab;
+const struct z_symtab_entry __symtab_entry * z_symtab_entries;
+const struct symtab_info __symtab_info z_symtab;