Error even w/warnings disabled for no-return fcns (#8495)

* Error even w/warnings disabled for no-return fcns

A function whose prototype says it will return a value but doesn't
is undefined behaviour in C++.  GCC 10 will generate code that crashes
in this case.

In warnings==None mode, insterad of turning off all warnings with
`-w`, explicitly list all G++ possible warnings except for the
`no-return` warning which catches this programming error.

* Use different lists for GCC vs G++

G++ and GCC have different warning options, so use different lists.

* Make separate file for each level, add readme

The readme now includes the exact commands required to regenerate the
none-XXX files, no manual editing needed.

* Address review comments, only adjusts G++/None

platform.txt

@@ -21,11 +21,11 @@ runtime.tools.mkdir={runtime.platform.path}/tools/mkdir.py
 runtime.tools.cp={runtime.platform.path}/tools/cp.py
 runtime.tools.eboot={runtime.platform.path}/bootloaders/eboot/eboot.elf
 
-compiler.warning_flags=-w -Werror=return-type
-compiler.warning_flags.none=-w -Werror=return-type
-compiler.warning_flags.default=-Werror=return-type
-compiler.warning_flags.more=-Wall -Werror=return-type
-compiler.warning_flags.all=-Wall -Wextra -Werror=return-type
+compiler.warning_flags=@{runtime.platform.path}/tools/warnings/none
+compiler.warning_flags.none=@{runtime.platform.path}/tools/warnings/none
+compiler.warning_flags.default=@{runtime.platform.path}/tools/warnings/default
+compiler.warning_flags.more=@{runtime.platform.path}/tools/warnings/more
+compiler.warning_flags.all=@{runtime.platform.path}/tools/warnings/extra
 
 build.lwip_lib=-llwip_gcc
 build.lwip_include=lwip/include
@@ -68,18 +68,18 @@ compiler.cpreprocessor.flags=-D__ets__ -DICACHE_FLASH -U__STRICT_ANSI__ -D_GNU_S
 compiler.libraries.ldflags=
 
 compiler.c.cmd=xtensa-lx106-elf-gcc
-compiler.c.flags=-c {compiler.warning_flags} -std=gnu17 {build.stacksmash_flags} -Os -g -free -fipa-pta -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}
+compiler.c.flags=-c {compiler.warning_flags}-gcc -std=gnu17 {build.stacksmash_flags} -Os -g -free -fipa-pta -Werror=return-type -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}
 
 compiler.S.cmd=xtensa-lx106-elf-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -MMD -mlongcalls "-I{runtime.tools.xtensa-lx106-elf-gcc.path}/include/"
 
-compiler.c.elf.flags=-g {compiler.warning_flags} -Os -nostdlib -Wl,--no-check-sections -u app_entry {build.float} -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/lib/{build.sdk}" "-L{build.path}" "-L{compiler.libc.path}/lib" "-Tlocal.eagle.flash.ld" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,spi_flash_read
+compiler.c.elf.flags=-g {compiler.warning_flags}-gcc -Os -nostdlib -Wl,--no-check-sections -u app_entry {build.float} -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/lib/{build.sdk}" "-L{build.path}" "-L{compiler.libc.path}/lib" "-Tlocal.eagle.flash.ld" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,spi_flash_read
 
 compiler.c.elf.cmd=xtensa-lx106-elf-gcc
 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
 
 compiler.cpp.cmd=xtensa-lx106-elf-g++
-compiler.cpp.flags=-c {compiler.warning_flags} {build.stacksmash_flags} -Os -g -free -fipa-pta -mlongcalls -mtext-section-literals -fno-rtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}
+compiler.cpp.flags=-c {compiler.warning_flags}-g++ {build.stacksmash_flags} -Os -g -free -fipa-pta -Werror=return-type -mlongcalls -mtext-section-literals -fno-rtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}
 
 compiler.as.cmd=xtensa-lx106-elf-as
 

tools/warnings/README.md

@@ -0,0 +1,12 @@
+These are the warning options for the compiler at different levels.
+
+Because G++ 10 produces code which crashes when a function is declared
+to return a value but doesn't (this is undefined per the C++ specs, but legal
+for C11 and above code as long as the [non]returned value is ignored), we
+cannot warn them if we use "-w" to disable all warnings, and instead have
+to delete every warning but "-Wreturn-type"
+
+Generate the "none-g++" file with the following command:
+````
+./tools/xtensa-lx106-elf/bin/xtensa-lx106-elf-gcc --help=warnings -Q | grep '\[enabled\]' | grep -v 'return-type' | awk '{print $1}' | sed 's/-W/-Wno-/' | grep -v = | grep -v -- -f | egrep -v '(c11-c2x-compat|c90-c99-compat|c99-c11-compat|declaration-after-statement|designated-init|discarded-array-qualifiers|discarded-qualifiers|implicit-int|incompatible-pointer-types|int-conversion|old-style-definition|override-init-side-effects|pointer-to-int-cast)' > tools/warnings/none-g++
+````

tools/warnings/extra-g++

@@ -0,0 +1 @@
+-Wall -Wextra

tools/warnings/extra-gcc

@@ -0,0 +1 @@
+-Wall -Wextra

tools/warnings/more-g++

@@ -0,0 +1 @@
+-Wall

tools/warnings/more-gcc

@@ -0,0 +1 @@
+-Wall

tools/warnings/none-g++

@@ -0,0 +1,52 @@
+-Wno-address-of-packed-member
+-Wno-aggressive-loop-optimizations
+-Wno-analyzer-malloc-leak
+-Wno-analyzer-null-argument
+-Wno-analyzer-null-dereference
+-Wno-analyzer-possible-null-argument
+-Wno-analyzer-possible-null-dereference
+-Wno-analyzer-stale-setjmp-buffer
+-Wno-analyzer-tainted-array-index
+-Wno-analyzer-unsafe-call-within-signal-handler
+-Wno-attribute-warning
+-Wno-attributes
+-Wno-builtin-declaration-mismatch
+-Wno-builtin-macro-redefined
+-Wno-cannot-profile
+-Wno-coverage-mismatch
+-Wno-cpp
+-Wno-deprecated
+-Wno-deprecated-declarations
+-Wno-div-by-zero
+-Wno-endif-labels
+-Wno-enum-compare
+-Wno-hsa
+-Wno-if-not-aligned
+-Wno-ignored-attributes
+-Wno-int-to-pointer-cast
+-Wno-invalid-memory-model
+-Wno-long-long
+-Wno-lto-type-mismatch
+-Wno-main
+-Wno-missing-profile
+-Wno-narrowing
+-Wno-odr
+-Wno-overflow
+-Wno-packed-bitfield-compat
+-Wno-pointer-compare
+-Wno-pragmas
+-Wno-prio-ctor-dtor
+-Wno-psabi
+-Wno-return-local-addr
+-Wno-shift-count-negative
+-Wno-shift-count-overflow
+-Wno-shift-negative-value
+-Wno-sizeof-array-argument
+-Wno-switch-bool
+-Wno-switch-outside-range
+-Wno-switch-unreachable
+-Wno-sync-nand
+-Wno-trigraphs
+-Wno-unused-result
+-Wno-varargs
+-Wno-vla

tools/warnings/none-gcc

@@ -0,0 +1 @@
+-w