Respect linking order of libraries

[maxgerhardt]

Fixes #8262.

Arduino IDE link order:

-lhal -lphy -lpp -lnet80211 -llwip2-536-feat -lwpa -lcrypto -lmain -lwps -lbearssl -lespnow -lsmartconfig -lairkiss -lwpa2 -lstdc++ -lm -lc -lgcc

PlatformIO link order before this fix:

-lhal -lphy -lpp -lnet80211 -lwpa -lcrypto -lmain -lwps -lbearssl -lespnow -lsmartconfig -lairkiss -lwpa2 -lm -lc -lgcc -llwip2-536-feat -lstdc++

(^ which causes the linking failure in regards to the math library in the referenced issue)

PlatformIO link order after this fix:

-lhal -lphy -lpp -lnet80211 -llwip2-536-feat -lwpa -lcrypto -lmain -lwps -lbearssl -lespnow -lsmartconfig -lairkiss -lwpa2 -lstdc++ -lm -lc -lgcc

Aka, now equivalent to the Arduino IDE linking order.

The code refactors setting env["LIBS"] further down the script where it knows the system libraries to be built, and then creates the array with the correct linking order.

The previous env.Append(LIBS = ...) is wrong here because it appends to the back and hence does not respect the original linker order laid out in the platform.txt

Arduino/platform.txt

Line 70 in 5f04fbb

compiler.c.elf.libs=-lhal -lphy -lpp -lnet80211 {build.lwip_lib} -lwpa -lcrypto -lmain -lwps -lbearssl -lespnow -lsmartconfig -lairkiss -lwpa2 {build.stdcpp_lib} -lm -lc -lgcc

[mcspr]

Initial LIBS could be left empty:

if EXCEPTIONS:
    CXX_LIBS = ["std++"]
else:
    CXX_LIBS = ["std++-noexc"]

SDK_LIBS = [
    "hal", "phy", "pp", "net80211", "wpa", "crypto", "main",
    "wps", "bearssl", "espnow", "smartconfig", "airkiss", "wpa2"
]

C_LIBS = [
    "m", "c", "gcc"
]

if BLAH:
    LWIP_LIBS = [ ... ]
# ...

env.Replace(LIBS=SDK_LIBS + LWIP_LIBS + CXX_LIBS + C_LIBS)

?

Hardcoded offsets are hard to parse at a glance

[maxgerhardt]

I'm not quite sure if I follow? The hardcoded offsets have been removed with the latest commit because I didn't like that style either. The code at the bottom with env.Append(LIBS=<correct array>) is always reached (not inside an if), so it can't be left empty after the script.

[mcspr]

Github interface caching is weird, looking at the Files changes does not always update to the latest version when new commits come in. Latest update pretty much does what I proposed, so lgtm :)

[maxgerhardt]

I think this is a straight-forward fix & improvement PR. Any thoughts on getting this merged?

[mcspr]

@ivankravets