pkg/aflow: infer the target architecture instead of hard-coding it

Since we have the target kernel config, we can technically decide if
it's amd64 or arm64 or what not based on the presence of certain kernel
config options.

This introduces a generic helper to help figure that out and uses it for
both build and reproduction.

Author: FlorentRevest

pkg/aflow/action/crash/reproduce.go

@@ -62,13 +62,17 @@ func reproduce(ctx *aflow.Context, args reproduceArgs) (reproduceResult, error)
 		if err := json.Unmarshal(args.VM, &vmConfig); err != nil {
 			return fmt.Errorf("failed to parse VM config: %w", err)
 		}
-		vmConfig["kernel"] = filepath.Join(args.KernelObj, filepath.FromSlash(build.LinuxKernelImage(targets.AMD64)))
+		arch, err := targets.ArchFromLinuxConfig(args.KernelConfig)
+		if err != nil {
+			return err
+		}
+		vmConfig["kernel"] = filepath.Join(args.KernelObj, filepath.FromSlash(build.LinuxKernelImage(arch)))
 		vmCfg, err := json.Marshal(vmConfig)
 		if err != nil {
 			return fmt.Errorf("failed to serialize VM config: %w", err)
 		}
 		cfg := mgrconfig.DefaultValues()
-		cfg.RawTarget = "linux/amd64"
+		cfg.RawTarget = "linux/" + arch
 		cfg.Workdir = filepath.Join(dir, "workdir")
 		cfg.Syzkaller = args.Syzkaller
 		cfg.KernelObj = args.KernelObj

pkg/aflow/action/kernel/build.go

@@ -40,8 +40,12 @@ func buildKernel(ctx *aflow.Context, args buildArgs) (buildResult, error) {
 		if err := osutil.WriteFile(filepath.Join(dir, ".config"), []byte(args.KernelConfig)); err != nil {
 			return err
 		}
-		target := targets.List[targets.Linux][targets.AMD64]
-		image := filepath.FromSlash(build.LinuxKernelImage(targets.AMD64))
+		arch, err := targets.ArchFromLinuxConfig(args.KernelConfig)
+		if err != nil {
+			return err
+		}
+		target := targets.List[targets.Linux][arch]
+		image := filepath.FromSlash(build.LinuxKernelImage(arch))
 		makeArgs := build.LinuxMakeArgs(target, targets.DefaultLLVMCompiler, targets.DefaultLLVMLinker,
 			"ccache", dir, runtime.NumCPU())
 		const compileCommands = "compile_commands.json"

sys/targets/targets.go

@@ -43,6 +43,7 @@ type Target struct {
 	SyscallTrampolines map[string]string
 	Addr2Line          func() (string, error)
 	KernelAddresses    KernelAddresses
+	KernelConfigs      []string
 
 	init      *sync.Once
 	initOther *sync.Once
@@ -281,6 +282,7 @@ var List = map[string]map[string]*Target{
 				DataStart: 0xffff880000000000,
 				DataEnd:   0xffff890000000000,
 			},
+			KernelConfigs: []string{"CONFIG_X86_64"},
 		},
 		I386: {
 			VMArch:           AMD64,
@@ -291,13 +293,15 @@ var List = map[string]map[string]*Target{
 			Triple:           "x86_64-linux-gnu",
 			KernelArch:       "i386",
 			KernelHeaderArch: "x86",
+			KernelConfigs:    []string{"CONFIG_X86_32"},
 		},
 		ARM64: {
 			PtrSize:          8,
 			PageSize:         4 << 10,
 			Triple:           "aarch64-linux-gnu",
 			KernelArch:       "arm64",
 			KernelHeaderArch: "arm64",
+			KernelConfigs:    []string{"CONFIG_ARM64"},
 		},
 		ARM: {
 			VMArch:           ARM64,
@@ -306,6 +310,7 @@ var List = map[string]map[string]*Target{
 			Triple:           "arm-linux-gnueabi",
 			KernelArch:       "arm",
 			KernelHeaderArch: "arm",
+			KernelConfigs:    []string{"CONFIG_ARM"},
 		},
 		MIPS64LE: {
 			PtrSize:          8,
@@ -314,6 +319,7 @@ var List = map[string]map[string]*Target{
 			Triple:           "mips64el-linux-gnuabi64",
 			KernelArch:       "mips",
 			KernelHeaderArch: "mips",
+			KernelConfigs:    []string{"CONFIG_MIPS", "CONFIG_64BIT", "CONFIG_CPU_LITTLE_ENDIAN"},
 		},
 		PPC64LE: {
 			PtrSize:          8,
@@ -322,6 +328,7 @@ var List = map[string]map[string]*Target{
 			Triple:           "powerpc64le-linux-gnu",
 			KernelArch:       "powerpc",
 			KernelHeaderArch: "powerpc",
+			KernelConfigs:    []string{"CONFIG_PPC64", "CONFIG_CPU_LITTLE_ENDIAN"},
 		},
 		S390x: {
 			PtrSize:          8,
@@ -339,13 +346,15 @@ var List = map[string]map[string]*Target{
 				// To work around this problem we therefore reroute the mmap syscall to the glibc mmap wrapper.
 				"mmap": "mmap",
 			},
+			KernelConfigs: []string{"CONFIG_S390", "CONFIG_64BIT"},
 		},
 		RiscV64: {
 			PtrSize:          8,
 			PageSize:         4 << 10,
 			Triple:           "riscv64-linux-gnu",
 			KernelArch:       "riscv",
 			KernelHeaderArch: "riscv",
+			KernelConfigs:    []string{"CONFIG_RISCV", "CONFIG_64BIT"},
 		},
 	},
 	FreeBSD: {
@@ -1124,3 +1133,22 @@ int main() { printf("Hello, World!\n"); }
 int main() { std::vector<int> v(10); }
 `
 )
+
+func ArchFromLinuxConfig(cfg string) (string, error) {
+	for arch, target := range List[Linux] {
+		if len(target.KernelConfigs) == 0 {
+			continue
+		}
+		match := true
+		for _, conf := range target.KernelConfigs {
+			if !strings.Contains(cfg, conf+"=y") {
+				match = false
+				break
+			}
+		}
+		if match {
+			return arch, nil
+		}
+	}
+	return "", fmt.Errorf("can't determine architecture from config")
+}