[request] add weak attribute in all dummy callback functions

[atesin]

hi, i am trying to write an i/o posix library, but i found i can't implement most callback functions because they are already harcoded with dummy ones that does nothing in libc_replacements.cpp core file

my request is to add weak attributes in all functions of that file, so we can replace syscall implementations for other systems/filesystems/devices/etc. in libraries if we need

... of course we can manually modify the file but is not so tidy that way (that is actually what i am doing for now), and not many people are familiar/relaxed with doing so also

programs will work the same way with weak functions, the only difference will be they could be reimplemented if needed, because if we try to compile now we get a 'multiple definition' error

btw, libc implementation in esp-core was done by integrating (incomplete) newlib library = https://sourceware.org/newlib/

[mcspr]

Don't think so? Weak is indeed used here for our code to modify some things, but libc replacements are intended for actual implementations that never appear in the base one to begin with.

But... If you happen to notice that newlib almost always separates implementations per-file. Doing the same here would happen to help with this exact problem, as symbol search with the current build commands would pick any overrides from extra .a files if they appear first

consider blah/cores/esp8266/libc_replacements_puts.cpp c/p from original one, with only puts
puts is removed from the original file

... headers ...

extern "C" {

int IRAM_ATTR puts(const char * str) {
    char c;
    while((c = *str) != 0) {
        ets_putc(c);
        ++str;
    }
    ets_putc('\n');
    return true;
}

};

sample project that has a lib intending to override stuff

arduino9315> fd
lib/
lib/bar/
lib/bar/bar.cpp
platformio.ini
src/
src/main.cpp

lib/bar/bar.cpp

#include <Arduino.h>

extern "C" {

void ets_putc(char);

int IRAM_ATTR puts(const char*) {
    ets_putc('\r');
    ets_putc('\n');
    return 1;
}

}

platformio rule to force lib build

[env]
platform = espressif8266 @ 4.2.1
framework = arduino
platform_packages =
    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git
build_flags = -Wall -Wextra -Werror

[env:d1_mini]
board = d1_mini
lib_deps =
    bar

dummy main file. using puts picks the one from lib/bar

#include <Arduino.h>

void setup() {
    puts("hello world"); // oops outputs just cr lf
}

void loop() {
}

Could be quite dangerous for debugging though
(like we happened upon with crc32 symbol some people used)

edit: obviously, you could also utilize platformio builder to copy objs and weaken symbols manually. or, use wrapping. likely more complicated for arduino(c) builder, unsure if they ever added compilation flags custumization or library inclusion that is obvious for the user