1. Context
While figuring out the ESP32 build system, I currently focus on how the ESP-IDF tool builds projects, and how Arduino IDE builds ESP projects on the other hand.
2. Questions
The ESP-IDF framework has a set of “component libraries”. In the Arduino IDE, they are available as precompiled archives. Comparing both raised a lot of questions to me. I’ll explain in the next paragraphs.
3. The Arduino "component libraries"
The Arduino IDE stores the ESP32 component libraries as archive files here:
~/.arduino15/packages/esp32/hardware/esp32/1.0.6/tools/sdk/lib/
I’m trying to figure out how these precompiled component libraries were built in the first place. Thanks to my previous question (see Where to find the archives source code? - ESP32 Forum) I now know where to find the source code for them. If you have the esp-idf tool installed, the source code can be found here:
~/esp/esp-idf/components/
Compiling this source code into those component libraries is not straightforward. This is what I do:
1. I launch a “Hello World” project with the esp-idf tool.
2. I replace the file
'~/esp/hello_world/sdkconfig'with'~/.arduino15/packages/esp32/hardware/esp32/1.0.6/tools/sdk/sdkconfig'. In other words, I try to apply the Arduino configurations onto my “Hello World” project.3. I build the “Hello World” project with full verbosity to see how the component libraries are built.
Since my “Hello World” project has now the exact same configuration settings as Arduino (thanks to replacing the 'sdkconfig' file), the esp component libraries that appear in my project’s build folder should be the same as those in the '~/.arduino15/packages/esp32/hardware/esp32/1.0.6/tools/sdk/lib/' folder. Is this correct?
If that’s correct, then the three-step-approach described above is sufficient to figure out how the component libraries were built for the Arduino IDE.
4. Linking the "component libraries" with the application code
The Arduino IDE uses its precompiled component libraries totally different from how ESP-IDF uses them in the linking step of the final application .elf file. This is how Arduino does it:
xtensa-esp32-elf-g++ -nostdlib
-L<esp-sdk>/lib
-L<esp-sdk>/ld
-T esp32_out.ld
-T esp32.project.ld
-T esp32.rom.ld
-T esp32.peripherals.ld
-T esp32.rom.libgcc.ld
-T esp32.rom.spiram_incompatible_fns.ld
-u esp_app_desc
-u ld_include_panic_highint_hdl
-u call_user_start_cpu0
-Wl,--gc-sections
-Wl,-static
-Wl,--undefined=uxTopUsedPriority
-u __cxa_guard_dummy
-u __cxx_fatal_exception
-Wl,--start-group
/tmp/arduino_build_852524/sketch/WiFiScan.ino.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/ETH.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFi.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiAP.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiClient.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiGeneric.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiMulti.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiSTA.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiScan.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiServer.cpp.o
/tmp/arduino_build_852524/libraries/WiFi/WiFiUdp.cpp.o
/tmp/arduino_build_852524/core/core.a
-lgcc
-lesp_websocket_client
-lwpa2
-ldetection
-lesp_https_server
-lwps
-lhal
-lconsole
-lpe
-lsoc
-lsdmmc
-lpthread
-llog
-lesp_http_client
-ljson
-lmesh
-lesp32-camera
-lnet80211
-lwpa_supplicant
-lc
-lmqtt
-lcxx
-lesp_https_ota
-lulp
-lefuse
-lpp
-lmdns
-lbt
-lwpa
-lspiffs
-lheap
-limage_util
-lunity
-lrtc
-lmbedtls
-lface_recognition
-lnghttp
-ljsmn
-lopenssl
-lcore
-lfatfs
-lm
-lprotocomm
-lsmartconfig
-lxtensa-debug-module
-ldl
-lesp_event
-lesp-tls
-lfd
-lespcoredump
-lesp_http_server
-lfr
-lsmartconfig_ack
-lwear_levelling
-ltcp_transport
-llwip
-lphy
-lvfs
-lcoap
-lesp32
-llibsodium
-lbootloader_support
-ldriver
-lcoexist
-lasio
-lod
-lmicro-ecc
-lesp_ringbuf
-ldetection_cat_face
-lapp_update
-lespnow
-lface_detection
-lapp_trace
-lnewlib
-lbtdm_app
-lwifi_provisioning
-lfreertos
-lfreemodbus
-lethernet
-lnvs_flash
-lspi_flash
-lc_nano
-lexpat
-lfb_gfx
-lprotobuf-c
-lesp_adc_cal
-ltcpip_adapter
-lstdc++
-Wl,--end-group
-Wl,-EL
-o /tmp/arduino_build_852524/WiFiScan.ino.elf
The precompiled component libraries are sitting in the folder <esp-sdk>/lib (actually in ~/.arduino15/packages/esp32/hardware/esp32/1.0.6/tools/sdk/lib, but I’m using some placeholders here for brevity). This folder is exposed to the linker through the -L<esp-sdk>/lib flag. After listing all the relevant object files of the application, the libraries are then passed to the linker with -l flags. The linker knows where to find them.
This is how the linking happens with the ESP-IDF tool:
xtensa-esp32-elf-g++ -mlongcalls
-Wno-frame-address
CMakeFiles/hello-world.elf.dir/project_elf_src_esp32.c.obj
-o hello-world.elf
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/asio/libasio.a
esp-idf/bt/libbt.a
esp-idf/cbor/libcbor.a
esp-idf/unity/libunity.a
esp-idf/cmock/libcmock.a
esp-idf/coap/libcoap.a
esp-idf/console/libconsole.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/esp_adc_cal/libesp_adc_cal.a
esp-idf/esp_hid/libesp_hid.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/protobuf-c/libprotobuf-c.a
esp-idf/protocomm/libprotocomm.a
esp-idf/mdns/libmdns.a
esp-idf/esp_local_ctrl/libesp_local_ctrl.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/esp_websocket_client/libesp_websocket_client.a
esp-idf/expat/libexpat.a
esp-idf/wear_levelling/libwear_levelling.a
esp-idf/fatfs/libfatfs.a
esp-idf/freemodbus/libfreemodbus.a
esp-idf/jsmn/libjsmn.a
esp-idf/json/libjson.a
esp-idf/libsodium/liblibsodium.a
esp-idf/mqtt/libmqtt.a
esp-idf/openssl/libopenssl.a
esp-idf/spiffs/libspiffs.a
esp-idf/ulp/libulp.a
esp-idf/wifi_provisioning/libwifi_provisioning.a
esp-idf/main/libmain.a
-Wl,--cref -Wl,--Map=/home/kristof/esp/hello_world/build/hello-world.map -Wl,--gc-sections -fno-rtti -fno-lto esp-idf/asio/libasio.a
esp-idf/cbor/libcbor.a
esp-idf/cmock/libcmock.a
esp-idf/unity/libunity.a
esp-idf/coap/libcoap.a
esp-idf/esp_adc_cal/libesp_adc_cal.a
esp-idf/esp_hid/libesp_hid.a
esp-idf/esp_local_ctrl/libesp_local_ctrl.a
esp-idf/esp_websocket_client/libesp_websocket_client.a
esp-idf/expat/libexpat.a
esp-idf/fatfs/libfatfs.a
esp-idf/wear_levelling/libwear_levelling.a
esp-idf/freemodbus/libfreemodbus.a
esp-idf/jsmn/libjsmn.a
esp-idf/libsodium/liblibsodium.a
esp-idf/mqtt/libmqtt.a
esp-idf/openssl/libopenssl.a
esp-idf/spiffs/libspiffs.a
esp-idf/wifi_provisioning/libwifi_provisioning.a
esp-idf/protocomm/libprotocomm.a
esp-idf/bt/libbt.a
-L/home/kristof/esp/esp-idf/components/bt/controller/lib/esp32 -lbtdm_app esp-idf/protobuf-c/libprotobuf-c.a
esp-idf/mdns/libmdns.a
esp-idf/console/libconsole.a
esp-idf/json/libjson.a
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a
esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a
esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a
esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a
esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a
esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a
esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a
esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a
esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a
esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a
esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/ulp/libulp.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcoexist.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcore.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libespnow.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libmesh.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libnet80211.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libpp.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libsmartconfig.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libwapi.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libphy.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/librtc.a
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a
esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a
esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a
esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a
esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a
esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a
esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a
esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a
esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a
esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a
esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/ulp/libulp.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcoexist.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcore.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libespnow.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libmesh.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libnet80211.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libpp.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libsmartconfig.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libwapi.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libphy.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/librtc.a
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a
esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a
esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a
esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a
esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a
esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a
esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a
esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a
esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a
esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a
esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/ulp/libulp.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcoexist.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcore.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libespnow.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libmesh.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libnet80211.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libpp.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libsmartconfig.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libwapi.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libphy.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/librtc.a
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a
esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a
esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a
esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a
esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a
esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a
esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a
esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a
esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a
esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a
esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/ulp/libulp.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcoexist.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcore.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libespnow.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libmesh.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libnet80211.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libpp.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libsmartconfig.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libwapi.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libphy.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/librtc.a
esp-idf/mbedtls/libmbedtls.a
esp-idf/efuse/libefuse.a
esp-idf/app_update/libapp_update.a
esp-idf/bootloader_support/libbootloader_support.a
esp-idf/esp_ipc/libesp_ipc.a
esp-idf/spi_flash/libspi_flash.a
esp-idf/nvs_flash/libnvs_flash.a
esp-idf/pthread/libpthread.a
esp-idf/esp_gdbstub/libesp_gdbstub.a
esp-idf/espcoredump/libespcoredump.a
esp-idf/esp_system/libesp_system.a
esp-idf/esp_rom/libesp_rom.a
esp-idf/hal/libhal.a
esp-idf/vfs/libvfs.a
esp-idf/esp_eth/libesp_eth.a
esp-idf/tcpip_adapter/libtcpip_adapter.a
esp-idf/esp_netif/libesp_netif.a
esp-idf/esp_event/libesp_event.a
esp-idf/wpa_supplicant/libwpa_supplicant.a
esp-idf/esp_wifi/libesp_wifi.a
esp-idf/lwip/liblwip.a
esp-idf/log/liblog.a
esp-idf/heap/libheap.a
esp-idf/soc/libsoc.a
esp-idf/esp_hw_support/libesp_hw_support.a
esp-idf/esp_pm/libesp_pm.a
esp-idf/esp_ringbuf/libesp_ringbuf.a
esp-idf/driver/libdriver.a
esp-idf/xtensa/libxtensa.a
esp-idf/perfmon/libperfmon.a
esp-idf/esp32/libesp32.a
esp-idf/esp_common/libesp_common.a
esp-idf/esp_timer/libesp_timer.a
esp-idf/freertos/libfreertos.a
esp-idf/newlib/libnewlib.a
esp-idf/cxx/libcxx.a
esp-idf/app_trace/libapp_trace.a
esp-idf/nghttp/libnghttp.a
esp-idf/esp-tls/libesp-tls.a
esp-idf/tcp_transport/libtcp_transport.a
esp-idf/esp_http_client/libesp_http_client.a
esp-idf/esp_http_server/libesp_http_server.a
esp-idf/esp_https_ota/libesp_https_ota.a
esp-idf/sdmmc/libsdmmc.a
esp-idf/esp_serial_slave_link/libesp_serial_slave_link.a
esp-idf/ulp/libulp.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcoexist.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libcore.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libespnow.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libmesh.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libnet80211.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libpp.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libsmartconfig.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libwapi.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/libphy.a
/home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32/librtc.a
-Wl,--wrap=mbedtls_mpi_exp_mod
-u esp_app_desc
-u pthread_include_pthread_impl
-u pthread_include_pthread_cond_impl
-u pthread_include_pthread_local_storage_impl
-u ld_include_panic_highint_hdl
-u start_app
-u start_app_other_cores
-L /home/kristof/esp/esp-idf/components/esp_rom/esp32/ld
-T esp32.rom.ld
-T esp32.rom.api.ld
-T esp32.rom.libgcc.ld
-T esp32.rom.newlib-data.ld
-T esp32.rom.syscalls.ld
-u vfs_include_syscalls_impl
-L /home/kristof/esp/esp-idf/components/esp_wifi/lib/esp32
/home/kristof/esp/esp-idf/components/xtensa/esp32/libxt_hal.a
-L /home/kristof/esp/hello_world/build/esp-idf/esp32
-T esp32_out.ld
-L /home/kristof/esp/hello_world/build/esp-idf/esp32/ld
-T esp32.project.ld
-L /home/kristof/esp/esp-idf/components/esp32/ld
-T esp32.peripherals.ld
-u call_user_start_cpu0
-mfix-esp32-psram-cache-issue
-mfix-esp32-psram-cache-strategy=memw
-Wl,--undefined=uxTopUsedPriority
-u app_main
-lm esp-idf/newlib/libnewlib.a
-u newlib_include_heap_impl
-u newlib_include_syscalls_impl
-u newlib_include_pthread_impl
-lgcc
-u __cxa_guard_dummy
-lstdc++ esp-idf/pthread/libpthread.a
esp-idf/app_trace/libapp_trace.a
-lgcov
esp-idf/app_trace/libapp_trace.a
-lgcov
-lc
The approach is a bit different. But the result should be the same: the archive files get passed to the linker, such that they are available to be linked against the application code.
However, what really troubles me is that some component libraries appear twice or more in the ESP-IDF linker call! Take for example the mbedtls library. The Arduino linker call passes this library to the linker just once:
xtensa-esp32-elf-g++
...
-lmbedtls
...
And if you look in the Arduino folder where the archive files are, you’ll find just one libmbedtls.a file. Now consider the ESP-IDF linker call, passing the mbedtls library multiple times:
xtensa-esp32-elf-g++
...
esp-idf/mbedtls/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
...
esp-idf/mbedtls/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedtls.a
esp-idf/mbedtls/mbedtls/library/libmbedcrypto.a
esp-idf/mbedtls/mbedtls/library/libmbedx509.a
...
You see, it not only gets passed multiple times to the linker, but there are even two different files with the name libmbedtls.a. Aside from that, there are also two other archive files that have something to do with this mbedtls library: libmbedcrypto.a and libmbedx509.a.
All of this confuses me. Why isn’t there just a single libmbedtls.a file produced by the ESP-IDF tool?
EDIT:
My colleague Johan explained me that adding the same archive file multiple times to the linker is an old trick to overcome circular dependencies. The Arduino IDE solves this by encapsulating the archive files between -Wl,--start-group and -Wl,--end-group flags. However, the other problem still remains: why are there two different libmbedtls.a files - one at ~/esp/hello_world/build/esp-idf/mbedtls/libmbedtls.a and the other at ~/esp/hello_world/build/esp-idf/mbedtls/mbedtls/library/libmbedtls.a?
Also, these two files are certainly not identical, if you look at how they are compiled. This is the compilation of ~/esp/hello_world/build/esp-idf/mbedtls/mbedtls/library/libmbedtls.a:
[ 58%] Linking CXX static library libmbedtls.a
cd /home/kristof/esp/hello_world/build/esp-idf/mbedtls/mbedtls/library
xtensa-esp32-elf-ar qc
libmbedtls.a
CMakeFiles/mbedtls.dir/debug.c.obj
CMakeFiles/mbedtls.dir/ssl_cache.c.obj
CMakeFiles/mbedtls.dir/ssl_ciphersuites.c.obj
CMakeFiles/mbedtls.dir/ssl_cli.c.obj
CMakeFiles/mbedtls.dir/ssl_cookie.c.obj
CMakeFiles/mbedtls.dir/ssl_srv.c.obj
CMakeFiles/mbedtls.dir/ssl_ticket.c.obj
CMakeFiles/mbedtls.dir/ssl_tls.c.obj
CMakeFiles/mbedtls.dir/__/__/port/mbedtls_debug.c.obj
CMakeFiles/mbedtls.dir/__/__/port/net_sockets.c.obj
xtensa-esp32-elf-ranlib libmbedtls.a
and this is the compilation of ~/esp/hello_world/build/esp-idf/mbedtls/libmbedtls.a:
[ 59%] Linking C static library libmbedtls.a
cd /home/kristof/esp/hello_world/build/esp-idf/mbedtls
xtensa-esp32-elf-ar qc
libmbedtls.a
CMakeFiles/__idf_mbedtls.dir/esp_crt_bundle/esp_crt_bundle.c.obj
CMakeFiles/__idf_mbedtls.dir/__/__/x509_crt_bundle.S.obj
xtensa-esp32-elf-ranlib libmbedtls.a