initial commitHEADmain

5 files changed, 86 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e389069
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*.sw?
+*.o
+./hi
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..1c6845e
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,15 @@
+# build image: latest alpine plus the following packages:
+# - binutils: for as and ld
+# - make: for gnu make
+FROM docker.io/alpine:latest AS build
+COPY . /src
+WORKDIR /src
+RUN apk add binutils make && \
+  make && \
+  wc -c ./hi
+
+# output image which contains a single 384 byte statically-linked arm64
+# binary named "/hi"
+FROM scratch
+COPY --from=build /src/hi /hi
+CMD ["/hi"]
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b5d8aae
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,15 @@
+APP=./hi
+OBJS=hi.o
+
+.PHONY=all
+
+all: $(APP)
+
+$(APP): $(OBJS)
+	ld -s -o $(APP) $(OBJS)
+
+hi.o: hi.s
+	as -o hi.o hi.s
+
+clean:
+	$(RM) $(APP) $(OBJS)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4b545d7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,22 @@
+Critical infrastructure.
+
+Compiles to 384 byte statically-linked arm64 linux binary and a ~4k
+container image.
+
+Build, run, and view binary size on an arm64 linux system:
+
+    > make
+    ...
+    > ./hi
+    alonzo sucks!
+    > wc -c ./hi
+    384 ./hi
+    >
+
+Build container image, then check image size:
+
+    > podman build -t hi:latest .
+    ...
+    > podman images --format '{{.Size}}' hi
+    3.83 kB
+    >
diff --git a/hi.s b/hi.s
new file mode 100644
index 0000000..90190cb
--- /dev/null
+++ b/hi.s
@@ -0,0 +1,31 @@
+// hi.s: print "alonzo sucks!" to standard output and then exit.
+//
+// uses write() and exit() linux system calls directly to elide libc and
+// assembles to a static, 384 byte arm64 binary.
+
+// entry point
+//
+// uses 32-bit registers (wN) instead of 64-bit registers (xN) to
+// save a few bytes in the assembled binary
+.text
+.global _start
+_start:
+  // write(stdout, msg, len)
+  mov w0, #1    // stdout fd (1)
+  ldr w1, =msg  // message
+  mov w2, len   // message length
+  mov w8, #64   // write() (64)
+  svc #0        // call write()
+
+  // exit(0)
+  mov w0, #0    // exit code (0)
+  mov w8, #93   // exit() (93)
+  svc #0        // call exit()
+
+// message and message length
+//
+// technically the message belongs in the .rodata section, but sticking
+// it here allows it to be packed after _start and the saves ~60 bytes
+// in the assembled binary
+msg: .ascii "alonzo sucks!\n" // message (14 bytes)
+len = . - msg // message length