[Discussion]How to elegantly implement ALLSYMS feat in CMake build

[xuxin930]

I planning to add ALLSYMS feature in CMake build system,
there is a issue I encountered and I hope to discuss it with you all.

Since we need to complete the final linking FIRST and then use the linked ELF to generate the symbol table.

nuttx/arch/sim/src/Makefile

Lines 354 to 365 in 53aef8e

	define LINK_ALLSYMS
	$(if $(CONFIG_HOST_MACOS), \
	$(Q) $(TOPDIR)/tools/mkallsyms.sh noconst $(NUTTX) $(CROSSDEV) > allsyms.tmp, \
	$(Q) $(TOPDIR)/tools/mkallsyms.py $(NUTTX) allsyms.tmp --orderbyname $(CONFIG_SYMTAB_ORDEREDBYNAME))
	$(Q) $(call COMPILE, allsyms.tmp, allsyms$(OBJEXT), -x c)
	$(if $(CONFIG_HAVE_CXX),\
	$(Q) "$(CXX)" $(CFLAGS) $(LDFLAGS) -o $(NUTTX) \
	$(HEADOBJ) nuttx.rel $(HOSTOBJS) $(STDLIBS) allsyms$(OBJEXT),\
	$(Q) "$(CC)" $(CFLAGS) $(LDFLAGS) -o $(NUTTX) \
	$(HEADOBJ) nuttx.rel $(HOSTOBJS) $(STDLIBS) allsyms$(OBJEXT))
	$(Q) $(call DELFILE, allsyms.tmp allsyms$(OBJEXT))
	endef

nuttx/arch/sim/src/Makefile

Lines 385 to 395 in 53aef8e

	ifneq ($(CONFIG_ALLSYMS),y)
	$(if $(CONFIG_HAVE_CXX),\
	$(Q) "$(CXX)" $(CFLAGS) $(LDFLAGS) -o $(TOPDIR)/$@ $(HEADOBJ) nuttx.rel $(HOSTOBJS) $(STDLIBS),\
	$(Q) "$(CC)" $(CFLAGS) $(LDFLAGS) -o $(TOPDIR)/$@ $(HEADOBJ) nuttx.rel $(HOSTOBJS) $(STDLIBS))
	else
	$(Q) # Link and generate default table
	$(Q) $(if $(wildcard $(shell echo $(NUTTX))),,$(call LINK_ALLSYMS, $@))
	$(Q) # Extract all symbols
	$(Q) $(call LINK_ALLSYMS, $^)
	$(Q) # Extract again since the table offset may changed
	$(Q) $(call LINK_ALLSYMS, $^)

---

this means:

1. allsyms.c is must generated after nuttx elf linking
2. we have to execute link multiple times, at least three times

this will cause problems when using CMake,
because we cannot add dependency to a target, and this dependency also depends on this target at the same time.

              need allsyms to gen final elf with syms
nuttx       --------------------------------------->     allsyms.c
         <---------------------------------------
               need nuttx elf to export symtable 

this creates circular dependency issues.

---

The solution I'm currently thinking of is this:

1. when ALLSYMS feature is enabled , add an empty allsyms.c file dependency for nuttx.
2. add post execution process , run mkallsym and link twice

It looks a bit like this

if(CONFIG_ALLSYMS)
  file(TOUCH ${CMAKE_BINARY_DIR}/allsyms.c) 
  add_library(allsyms OBJECT)
  nuttx_add_library_internal(allsyms)
  target_compile_definitions(allsyms PRIVATE $<TARGET_PROPERTY:nuttx,NUTTX_KERNEL_DEFINITIONS>)
  target_compile_options(allsyms PRIVATE $<TARGET_PROPERTY:nuttx,NUTTX_KERNEL_COMPILE_OPTIONS>)
  target_sources(allsyms PUBLIC ${CMAKE_BINARY_DIR}/allsyms.c)
  add_dependencies(nuttx allsyms) 

  add_custom_command(
    TARGET nuttx
    POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E remove allsyms.c
    COMMAND ${NUTTX_DIR}/tools/mkallsyms.py ${CMAKE_BINARY_DIR}/nuttx allsyms.c
    COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} -t nuttx
    COMMAND ${CMAKE_COMMAND} -E remove allsyms.c
    COMMAND ${NUTTX_DIR}/tools/mkallsyms.py ${CMAKE_BINARY_DIR}/nuttx allsyms.c
    COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} -t nuttx
    DEPENDS nuttx 
    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
    COMMAND_EXPAND_LISTS) 
endif()

---

What I doubt is whether it is reasonable to run cmake --build during the cmake call ？
although it will ONLY re-execute the action of generating allsyms.o
Is there a better way to solve this problem that I don't know of ?

[xuxin930]

hi @xiaoxiang781216 @anchao @raiden00pl @acassis
Do you have any suggestions? 😃

[anchao]

How about adding multiple execution targets?

add_executable(nuttx)
add_executable(nuttx_allsyms1)
add_executable(nuttx_allsyms2)

and update allsyms.o by nesting add_custom_command() POST_BUILD.

[xuxin930]

How about adding multiple execution targets?

Okay let me give it a try

[xuxin930]

How about adding multiple execution targets?

add_executable(nuttx)
add_executable(nuttx_allsyms1)
add_executable(nuttx_allsyms2)

and update allsyms.o by nesting add_custom_command() POST_BUILD.

This plan is perfect, and much better than what I designed before, 👍
@anchao thank you very much. I submitted in this PR #12035