Add some building documentation that clarifies the make targets

Split most of the work off into make/base.mk and allow for easy wrappers
to be created around that that can build with different instrumentation
in their own build directory.

Create wrappers for the following:
 - release build
 - debug build
 - afl++ fuzzing build
 - static analysis with clang
 - clang memory sanitizer
 - clang address/undefined sanitizer

Makefile

@@ -19,7 +19,7 @@ asan:
 	make -rRf make/asan.mk all
 
 msan:
-	make -rRf make/asan.mk all
+	make -rRf make/msan.mk all
 
 validate: asan msan debug
 	./validate.sh

doc/BUILDING.md

@@ -0,0 +1,29 @@
+# Building
+
+To build oas in the default configuration you just need (gnu) make and a
+sufficiently modern clang.
+
+```
+make
+```
+
+## Make targets
+
+There are a number of make targets available to build various instrumented
+builds that are used in validation, analysis and sanitizing. Some of these may
+require extra dependencies.
+
+
+ - `debug`: Creates the debug build in `build/debug`. This is the default target.
+ - `all`: Builds all binary executable targets. These are
+   `debug`, `release`, `msan`, `asan` and `afl`. All executables can be found
+   in `build/` in a subdirectory matching their target names.
+ - `release`: Creates the release build in `build/release`
+ - `afl`: Creates a build with AFL++ instrumentation for fuzzing
+ - `fuzz`: Starts the fuzzer with the instrumented afl executable
+ - `asan`: builds with the address and undefined clang sanitizers
+ - `msan`: builds with the memory clang sanitizer
+ - `validate`: Builds `debug`, `msan`, and `asan` targets, then runs the
+   validation script. This script executes the sanitizer targets and runs
+   Valgrind on the debug target across multiple modes and test input files.
+

make/analyze.mk

@@ -2,7 +2,7 @@ BUILD_DIR=build/analyze/
 -include make/base.mk
 
 analyze:
-	mkdir z-p reports/static-analysis
+	mkdir -p reports/static-analysis
 	scan-build -o reports/static-analysis/ -plist-html --status-bugs make -rRf make/analyze.mk all
 
 distclean: clean

make/asan.mk

@@ -1,5 +1,5 @@
 CFLAGS=-Wall -Wextra -Wpedantic -O0 -g3 -std=c23 -fno-omit-frame-pointer -fno-optimize-sibling-calls -D_POSIX_C_SOURCE=200809L -fsanitize=address,undefined
 LDFLAGS=-fsanitize=address,undefined
-BUILD_DIR=build/msan/
+BUILD_DIR=build/asan/
 
 -include make/base.mk

make/base.mk

@@ -24,4 +24,4 @@ $(BUILD_DIR)%.o: %.c
 -include $(DEPENDENCIES)
 
 clean:
-	rm -f $(BUILD_DIR)$(TARGET) $(OBJECTS)
+	rm -rf $(BUILD_DIR)

make/release.mk

@@ -1,5 +1,3 @@
-CC?=clang
-LD?=clang
 CFLAGS?=-Wall -Wextra -Wpedantic -O2 -std=c23 -flto -fomit-frame-pointer -DNDEBUG -D_POSIX_C_SOURCE=200809L
 LDFLAGS?=-flto -s -Wl,--gc-sections
 BUILD_DIR?=build/release/