Build: add initial appimage building scripts

Makefile

@@ -28,3 +28,5 @@ release: rnnoise
 	git describe --tags > bin/version.txt
 rnnoise:
 	$(MAKE) -C c/ladspa
+appimage:
+	VERSION=${VERSION} ./build-appimage.sh

build-appimage.sh

@@ -0,0 +1,97 @@
+#!/bin/sh
+#
+# Unforuntately we can't use regular AppImage tooling to build an AppImage.
+# The reason for that is that we require CAP_SYS_RESOURCE, which doesn't
+# work from FUSE mounted SquashFS, because it's mounted with 'nosuid'.
+# Interestingly, it seem the process is also not allowed to inherit
+# CAP_SYS_RESOURCE while the mount has nosuid. Our only option is to
+# make what appimage calls the "runtime", the thing thats supposed to
+# mount the embedded SquashFS, our application itself. And use the SquashFS
+# only for carrying around metadata, like the icon and .desktop file.
+# This means you cannot unpack and run this AppImage, to do that,
+# we'd have to include a copy of noisetorch *again*, basically doubling the
+# size. Doesn't seem worth it, let's break spec here.
+#
+
+WORK=`mktemp -d`
+OUTNAME="NoiseTorch-x86_64.AppImage"
+
+go generate
+
+#create mostly empty object file
+touch $WORK/empty.c
+
+gcc -c $WORK/empty.c -o $WORK/empty.o
+rm $WORK/empty.c
+
+#insert the sections we want into the object with objcopy
+#echo "zsync-something|justatest" > $WORK/upd_info
+printf "\0" > $WORK/upd_info
+objcopy  --add-section .upd_info=$WORK/upd_info --set-section-flags .upd_info=noload,readonly $WORK/empty.o #add section with objcopy
+rm $WORK/upd_info
+
+#echo "sig key goes here" > $WORK/sig_key
+printf "\0" > $WORK/sig_key
+objcopy  --add-section .sig_key=$WORK/sig_key --set-section-flags .sig_key=noload,readonly $WORK/empty.o
+rm $WORK/sig_key
+
+#echo "hash_placeholder_must_be_filed_after_this_should_be_nullbytes" > $WORK/sha256
+printf "\0" > $WORK/sha256
+objcopy  --add-section .sha256_sig=$WORK/sha256 --set-section-flags .sha256_sig=noload,readonly $WORK/empty.o #add section with objcopy
+rm $WORK/sha256
+
+
+#i'm sure there's a way to get an *actually* empty object file first.
+#or a better way in general to get an object with our sections
+#but.... this kinda works for now, so....
+objcopy --remove-section=.comment $WORK/empty.o
+objcopy --remove-section=.data $WORK/empty.o
+objcopy --remove-section=.text $WORK/empty.o
+objcopy --remove-section=.bss $WORK/empty.o
+objcopy --remove-section=.note.GNU-stack $WORK/empty.o
+objcopy --remove-section=.note.gnu.property $WORK/empty.o
+objdump -x $WORK/empty.o
+
+
+
+#link the created object into our app so we get the sections
+#why musl? because, as far as i understand, if we set linkmode=external, then go
+#doesn't include it's startup code, e.g _rt0_amd64 but instead expects _start to do
+#c-style init. But if we link with -nostdlib then we don't get _start and you can't run the app.
+#but if we do have the c stdlib, it's glibc for most people which can't be statically linked.
+#so, we need to link with musl to get a static binary and be able to include our object here.
+CC=musl-gcc go build -o "$OUTNAME" -ldflags="-linkmode=external -extldflags \"$WORK/empty.o -static\" -X main.version=${VERSION} -X main.distribution=official-appimage"
+strip "$OUTNAME"
+rm $WORK/empty.o
+
+
+#write app image 2 magic bytes
+printf "AI\02" | dd of="$OUTNAME" bs=1 count=3 seek=8 conv=notrunc
+
+#append squashfs with metadata
+mkdir $WORK/sqfs
+
+# the second copy of ourself INSIDE the app image, that is never used if launched via the "runtime"
+CGO_ENABLED=0 GOOS=linux go build -o $WORK/sqfs/AppRun -trimpath -tags release -a -ldflags "-s -w -extldflags \"-static\" -X main.version=${VERSION} -X main.distribution=official-appimage-inner" .
+# echo "#!/bin/sh" > $WORK/sqfs/AppRun
+# echo "echo 'This application cannot be ran in unpacked AppDir mode.'" >> $WORK/sqfs/AppRun
+# echo "echo 'Sorry about that.'" >> $WORK/sqfs/AppRun
+# echo "echo 'If you wonder why, it is because hacks were required to make it work at all.'" >> $WORK/sqfs/AppRun
+chmod +x $WORK/sqfs/AppRun
+
+cp assets/noisetorch.desktop $WORK/sqfs/
+echo "X-AppImage-Version=$(git describe --tags)">>$WORK/sqfs/noisetorch.desktop
+cp assets/icon/noisetorch.png $WORK/sqfs/.DirIcon
+mksquashfs $WORK/sqfs/* $WORK/sqfs/.* $WORK/out.sqfs
+
+rm $WORK/sqfs/.DirIcon
+rm $WORK/sqfs/noisetorch.desktop
+rm $WORK/sqfs/AppRun
+rmdir $WORK/sqfs
+
+cat $WORK/out.sqfs >> "$OUTNAME"
+
+rm $WORK/out.sqfs
+
+
+rmdir $WORK