Support C++ in app-layer

[jonasdn]

• Kbuild: Add support for C++ (.cc and .cpp) source
• app-layer: Add C++ example app

Fixes: #960

[ntamas]

It works! At least with the changes I outlined above. The part that was not working is that I was adding an extra include folder to the build in Kbuild with subdir-ccflags-y += -I$(srctree)/app/vendor/some-library/include and it was not picked up until I switched to _c_flags.

Thanks for the quick fix!

[jonasdn]

Thank you for testing it out! Could you try with the last commit: "Kbuild: Use cxx_flags for C++" ? To see if it solves your last issue.

[ntamas]

Yes, it works now! One tiny nitpick is that the output now shows CC something.o for C compilations but arm-none-eabi-g++ something.o for C++ files (and for some reason it includes the full path), but I couldn't figure out where this output is coming from. It doesn't bother me, but if you are super pedantic, this is the only issue left :)

[jonasdn]

Yes, it works now! One tiny nitpick is that the output now shows CC something.o for C compilations but arm-none-eabi-g++ something.o for C++ files (and for some reason it includes the full path), but I couldn't figure out where this output is coming from. It doesn't bother me, but if you are super pedantic, this is the only issue left :)

Thanks!

It was a typo $(CXX) vs CXX, fixed in latest commit.

 CXX     /home/jonasdn/sandbox/kbuild-firmware/examples/app_hello_world-cpp/src/hello_world.o

[tobbeanton]

Looks good!

[jonasdn]

Yes, it works now! One tiny nitpick is that the output now shows CC something.o for C compilations but arm-none-eabi-g++ something.o for C++ files (and for some reason it includes the full path), but I couldn't figure out where this output is coming from. It doesn't bother me, but if you are super pedantic, this is the only issue left :)

Thanks!

It was a typo $(CXX) vs CXX, fixed in latest commit.

 CXX     /home/jonasdn/sandbox/kbuild-firmware/examples/app_hello_world-cpp/src/hello_world.o

The full-path I think is an artifact of the oot build.

[ntamas]

Before you guys merge this, here's a proposed patch to the build system that gets rid of some annoying clang warnings when building Kbuild itself on macOS:

diff --git a/tools/kbuild/Makefile.kbuild b/tools/kbuild/Makefile.kbuild
index 017ad491..fd7586c6 100644
--- a/tools/kbuild/Makefile.kbuild
+++ b/tools/kbuild/Makefile.kbuild
@@ -217,12 +217,17 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
 HOSTCC       = gcc
 HOSTCXX      = g++
 HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2
-HOSTCFLAGS  += -fomit-frame-pointer -Wno-format-overflow -std=gnu89
+HOSTCFLAGS  += -fomit-frame-pointer -std=gnu89
 HOSTCXXFLAGS = -O2

 ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
+# These flags are clang-only
 HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
-               -Wno-missing-field-initializers -fno-delete-null-pointer-checks
+               -Wno-missing-field-initializers -fno-delete-null-pointer-checks \
+               -Wno-format-security
+else
+# These flags are gcc-only
+HOSTCFLAGS  += -Wno-format-overflow
 endif

 # Decide whether to build built-in, modular, or both.

(Sent this earlier on Discord).

---

Edit: this is on an Apple M1 CPU with clang 13, not sure whether it appears on Intel Macs.

[jonasdn]

Before you guys merge this, here's a proposed patch to the build system that gets rid of some annoying clang warnings when building Kbuild itself on macOS:

diff --git a/tools/kbuild/Makefile.kbuild b/tools/kbuild/Makefile.kbuild
index 017ad491..fd7586c6 100644
--- a/tools/kbuild/Makefile.kbuild
+++ b/tools/kbuild/Makefile.kbuild
@@ -217,12 +217,17 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
 HOSTCC       = gcc
 HOSTCXX      = g++
 HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2
-HOSTCFLAGS  += -fomit-frame-pointer -Wno-format-overflow -std=gnu89
+HOSTCFLAGS  += -fomit-frame-pointer -std=gnu89
 HOSTCXXFLAGS = -O2

 ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
+# These flags are clang-only
 HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
-               -Wno-missing-field-initializers -fno-delete-null-pointer-checks
+               -Wno-missing-field-initializers -fno-delete-null-pointer-checks \
+               -Wno-format-security
+else
+# These flags are gcc-only
+HOSTCFLAGS  += -Wno-format-overflow
 endif

 # Decide whether to build built-in, modular, or both.

(Sent this earlier on Discord).

Edit: this is on an Apple M1 CPU with clang 13, not sure whether it appears on Intel Macs.

Thanks I will test this a bit and add as a separate PR!