Incorrect use of __attribute__((weak)) in flash_hal

[ErikBogg]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: other
• Core Version: 3.1.1
• Development Env: Arduino IDE
• Operating System: Windows

Settings in IDE

• Module: Generic ESP8266 Module

Problem Description

When adding the line:
FLASH_MAP_SETUP_CONFIG(FLASH_MAP_MAX_FS)
in my sketch, I get a "multiple definition of `__flashdesc';"

The problem is that the assignment of __flashdesc on line 46 in flash_hal.h does not contain the 'attr' argument passed to the macro. So when the line 75 in flash_hal.cpp:
FLASH_MAP_SETUP_CONFIG_ATTR(__attribute__((weak)), FLASH_MAP_OTA_FS)
assigns __flashdesc to FLASH_MAP_OTA_FS, there is no weak assignment which makes it impossible override in user application.

Work-around until it is solved

Remove line 75 in flash_hal.cpp

Links to similar topics

https://forum.arduino.cc/t/multiple-definition-of-flashdesc-when-using-flash-map-setup-config/1098083/1

[ErikBogg]

Patch to solve the issue:

diff --git a/cores/esp8266/flash_hal.h b/cores/esp8266/flash_hal.h
index 682e1dcf..061b1d0b 100644
--- a/cores/esp8266/flash_hal.h
+++ b/cores/esp8266/flash_hal.h
@@ -43,7 +43,7 @@ extern const flash_map_s __flashdesc[];

 #define FLASH_MAP_SETUP_CONFIG(conf) FLASH_MAP_SETUP_CONFIG_ATTR(,conf)
 #define FLASH_MAP_SETUP_CONFIG_ATTR(attr, conf...) \
-  const flash_map_s __flashdesc[] PROGMEM = conf; \
+  extern const flash_map_s __flashdesc[] PROGMEM attr = conf; \
   const char *flashinit (void) attr; \
   const char *flashinit (void) \
   { \

[ErikBogg]

#8884

[d-a-v]

I wonder why extern is needed on your setup, one should get this warning:
warning: ‘__flashdesc’ initialized and declared ‘extern’.
What happens when you omit extern ?

But I agree on the missing attr, and I don't explain yet why it is not needed on my setup.

[ErikBogg]

Without extern you have an error like:
flash_hal.h:46:21: error: weak declaration of '__flashdesc' must be public

[mcspr]

why it is not needed on my setup.

Multiple compilation units using flash_hal.h? Not using either SPIFFS of LittleFS won't trigger the issue.

Without extern you have an error like:

I think the question is why we have to write extern when it is already a public symbol.
And the answer is - GCC has a bug :)
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83271

[d-a-v]

Agreed, I can indeed reproduce when effectively using a FS.

[d-a-v]

Closing per #8884, thanks @ErikBogg