simplify loading interpreter

Reviewed-on: #1

README.md

@@ -26,6 +26,8 @@ zig build
 Alternatively use something like this to run directly:
 ```sh
 zig build run -- /bin/ls
+# or
+zig build run -- ls
 ```
 
 This runs the tests:
@@ -44,6 +46,10 @@ passed through to the target executable.
 # Run a test executable that prints its arguments
 ./zig-out/bin/loader ./zig-out/bin/test_nolibc_pie_printArgs foo bar baz
 # Output: ./zig-out/bin/test_nolibc_pie_printArgs foo bar baz
+
+# Run echo
+./zig-out/bin/loader echo Hello There
+# Output: Hello There
 ```
 
 ## License

build.zig

@@ -42,17 +42,20 @@ pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
 
-    try compileTestApplications(b, target, optimize, false, false);
+    const faller = b.dependency("faller", .{
-    try compileTestApplications(b, target, optimize, false, true);
+        .target = target,
-    try compileTestApplications(b, target, optimize, true, true);
+        .optimize = optimize,
+    });
 
-    const mod = b.addModule("loader", .{
+    const mod = b.createModule(.{
         .root_source_file = b.path("src/main.zig"),
         .optimize = optimize,
         .target = target,
         .link_libc = false,
         .link_libcpp = false,
     });
+    mod.addImport("faller", faller.module("faller"));
+
     const exe = b.addExecutable(.{
         .name = "loader",
         .root_module = mod,
@@ -68,6 +71,10 @@ pub fn build(b: *std.Build) !void {
         run_cmd.addArgs(args);
     }
 
+    try compileTestApplications(b, target, optimize, false, false);
+    try compileTestApplications(b, target, optimize, false, true);
+    try compileTestApplications(b, target, optimize, true, true);
+
     const exe_tests = b.addTest(.{ .root_module = mod });
     const run_exe_tests = b.addRunArtifact(exe_tests);
     const test_step = b.step("test", "Run tests");

build.zig.zon

@@ -1,6 +1,12 @@
 .{
     .name = .loader,
     .version = "0.0.1",
+    .dependencies = .{
+        .faller = .{
+            .url = "git+https://git.pascalzittlau.de/pzittlau/faller.git#2dea92dcd9184c3a37f07761009944bc8fd4d352",
+            .hash = "faller-0.1.0-nNGNDT07AADmPJe_o0ERuMpZJGgXbdb_5B7VAMs2SmEt",
+        },
+    },
     .minimum_zig_version = "0.15.1",
     .paths = .{""},
     .fingerprint = 0xbf53f276a39b2af9,

src/main.zig

@@ -1,3 +1,4 @@
+const faller = @import("faller");
 const std = @import("std");
 
 const elf = std.elf;
@@ -5,10 +6,11 @@ const mem = std.mem;
 const posix = std.posix;
 const testing = std.testing;
 
-const assert = std.debug.assert;
+pub const faller_options: faller.Options = .{ .tags_disabled = &.{.debug} };
+const Logger = faller.Logger(&.{.loader});
 
-const log = std.log.scoped(.loader);
+const assert = std.debug.assert;
-pub const std_options = std.Options{ .log_level = .info };
+const log = Logger.log;
 
 const page_size = std.heap.pageSize();
 const max_interp_path_length = 128;
@@ -39,55 +41,43 @@ pub fn main() !void {
         return;
     }
 
-    // TODO: maybe search for the file in PATH
     // Map file into memory
-    const file = try std.fs.cwd().openFile(
+    const file = try lookupFile(mem.sliceTo(std.os.argv[arg_index], 0));
-        mem.sliceTo(std.os.argv[arg_index], 0),
+    var file_buffer: [128]u8 = undefined;
-        .{ .mode = .read_only },
+    var file_reader = file.reader(&file_buffer);
-    );
+    log(.info, "--- Loading executable: {s} ---", .{std.os.argv[arg_index]});
-    var buffer: [128]u8 = undefined;
-    var file_reader = file.reader(&buffer);
-    log.info("--- Loading executable: {s} ---", .{std.os.argv[arg_index]});
     const ehdr = try elf.Header.read(&file_reader.interface);
     const base = try loadStaticElf(ehdr, &file_reader);
     const entry = ehdr.entry + if (ehdr.type == .DYN) base else 0;
-    log.info("Executable loaded: base=0x{x}, entry=0x{x}", .{ base, entry });
+    log(.info, "Executable loaded: base=0x{x}, entry=0x{x}", .{ base, entry });
 
     // Check for dynamic linker
-    const maybe_interp: ?std.fs.File = interp: {
+    var maybe_interp_base: ?usize = null;
+    var maybe_interp_entry: ?usize = null;
     var phdrs = ehdr.iterateProgramHeaders(&file_reader);
     while (try phdrs.next()) |phdr| {
         if (phdr.p_type != elf.PT_INTERP) continue;
+
         var interp_path: [max_interp_path_length]u8 = undefined;
         try file_reader.seekTo(phdr.p_offset);
         if (try file_reader.read(interp_path[0..phdr.p_filesz]) != phdr.p_filesz)
             return UnfinishedReadError.UnfinishedRead;
         assert(interp_path[phdr.p_filesz - 1] == 0); // Must be zero terminated
-            log.info("Found interpreter path: {s}", .{interp_path[0 .. phdr.p_filesz - 1]});
+        log(.info, "Found interpreter path: {s}", .{interp_path[0 .. phdr.p_filesz - 1]});
-            break :interp try std.fs.cwd().openFile(
+        const interp = try std.fs.cwd().openFile(
             interp_path[0 .. phdr.p_filesz - 1],
             .{ .mode = .read_only },
         );
-        }
-        break :interp null;
-    };
 
-    // We don't need the file anymore. But we reuse the buffer if we need to load the interpreter.
+        log(.info, "--- Loading interpreter ---", .{});
-    // Therefore deinit everything.
+        var interp_buffer: [128]u8 = undefined;
-    file_reader = undefined;
+        var interp_reader = interp.reader(&interp_buffer);
-    file.close();
-
-    var maybe_interp_base: ?usize = null;
-    var maybe_interp_entry: ?usize = null;
-    if (maybe_interp) |interp| {
-        log.info("--- Loading interpreter ---", .{});
-        var interp_reader = interp.reader(&buffer);
         const interp_ehdr = try elf.Header.read(&interp_reader.interface);
         assert(interp_ehdr.type == elf.ET.DYN);
         const interp_base = try loadStaticElf(interp_ehdr, &interp_reader);
         maybe_interp_base = interp_base;
         maybe_interp_entry = interp_ehdr.entry + if (interp_ehdr.type == .DYN) interp_base else 0;
-        log.info("Interpreter loaded: base=0x{x}, entry=0x{x}", .{ interp_base, maybe_interp_entry.? });
+        log(.info, "Interpreter loaded: base=0x{x}, entry=0x{x}", .{ interp_base, maybe_interp_entry.? });
         interp.close();
     }
 
@@ -115,7 +105,8 @@ pub fn main() !void {
     const dest_ptr = @as([*]u8, @ptrCast(std.os.argv.ptr));
     const src_ptr = @as([*]u8, @ptrCast(&std.os.argv[arg_index]));
     const len = @intFromPtr(end_of_auxv) - @intFromPtr(src_ptr);
-    log.debug(
+    log(
+        .debug,
         "Copying stack from {*} to {*} with length 0x{x}",
         .{ src_ptr, dest_ptr, len },
     );
@@ -126,10 +117,10 @@ pub fn main() !void {
     // start of the stack.
     const argc: [*]usize = @as([*]usize, @ptrCast(@alignCast(&std.os.argv.ptr[0]))) - 1;
     argc[0] = std.os.argv.len - arg_index;
-    log.debug("new argc: {x}", .{argc[0]});
+    log(.debug, "new argc: {x}", .{argc[0]});
 
     const final_entry = maybe_interp_entry orelse entry;
-    log.info("Trampolining to final entry: 0x{x} with sp: {*}", .{ final_entry, argc });
+    log(.info, "Trampolining to final entry: 0x{x} with sp: {*}", .{ final_entry, argc });
     trampoline(final_entry, argc);
 }
 
@@ -155,15 +146,15 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
         }
         minva = mem.alignBackward(usize, minva, page_size);
         maxva = mem.alignForward(usize, maxva, page_size);
-        log.debug("Calculated bounds: minva=0x{x}, maxva=0x{x}", .{ minva, maxva });
+        log(.debug, "Calculated bounds: minva=0x{x}, maxva=0x{x}", .{ minva, maxva });
         break :bounds .{ minva, maxva };
     };
 
     // Check, that the needed memory region can be allocated as a whole. We do this
     const dynamic = ehdr.type == elf.ET.DYN;
-    log.debug("ELF type is {s}", .{if (dynamic) "DYN" else "EXEC (static)"});
+    log(.debug, "ELF type is {s}", .{if (dynamic) "DYN" else "EXEC (static)"});
     const hint = if (dynamic) null else @as(?[*]align(page_size) u8, @ptrFromInt(minva));
-    log.debug("mmap pre-flight hint: {*}", .{hint});
+    log(.debug, "mmap pre-flight hint: {*}", .{hint});
     const base = try posix.mmap(
         hint,
         maxva - minva,
@@ -172,7 +163,7 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
         -1,
         0,
     );
-    log.debug("Pre-flight reservation successful at: {*}, size: 0x{x}", .{ base.ptr, base.len });
+    log(.debug, "Pre-flight reservation successful at: {*}, size: 0x{x}", .{ base.ptr, base.len });
     posix.munmap(base);
 
     const flags = posix.MAP{ .TYPE = .PRIVATE, .ANONYMOUS = true, .FIXED = true };
@@ -188,7 +179,8 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
         var start = mem.alignBackward(usize, phdr.p_vaddr, page_size);
         const base_for_dyn = if (dynamic) @intFromPtr(base.ptr) else 0;
         start += base_for_dyn;
-        log.debug(
+        log(
+            .debug,
             "  - phdr[{}]: mapping 0x{x} bytes at 0x{x} (vaddr=0x{x}, dyn_base=0x{x})",
             .{ phdr_idx, size, start, phdr.p_vaddr, base_for_dyn },
         );
@@ -208,7 +200,7 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
             return UnfinishedReadError.UnfinishedRead;
         try posix.mprotect(ptr, elfToMmapProt(phdr.p_flags));
     }
-    log.debug("loadElf returning base: 0x{x}", .{@intFromPtr(base.ptr)});
+    log(.debug, "loadElf returning base: 0x{x}", .{@intFromPtr(base.ptr)});
     return @intFromPtr(base.ptr);
 }
 
@@ -221,6 +213,32 @@ fn elfToMmapProt(elf_prot: u64) u32 {
     return result;
 }
 
+/// Opens the file by either opening via a (absolute or relative) path or searching through `PATH`
+/// for a file with the name.
+fn lookupFile(path_or_name: []const u8) !std.fs.File {
+    // If filename contains a slash ("/"), then it is interpreted as a pathname.
+    if (std.mem.indexOfScalarPos(u8, path_or_name, 0, '/')) |_| {
+        const fd = try posix.open(path_or_name, .{ .ACCMODE = .RDONLY, .CLOEXEC = true }, 0);
+        return .{ .handle = fd };
+    }
+
+    // If it has no slash we need to look it up in PATH.
+    if (posix.getenvZ("PATH")) |env_path| {
+        var paths = std.mem.tokenizeScalar(u8, env_path, ':');
+        while (paths.next()) |p| {
+            var dir = std.fs.openDirAbsolute(p, .{}) catch continue;
+            defer dir.close();
+            const fd = posix.openat(dir.fd, path_or_name, .{
+                .ACCMODE = .RDONLY,
+                .CLOEXEC = true,
+            }, 0) catch continue;
+            return .{ .handle = fd };
+        }
+    }
+
+    return error.FileNotFound;
+}
+
 /// This function performs the final jump into the loaded program (amd64)
 // TODO: support more architectures
 fn trampoline(entry: usize, sp: [*]usize) noreturn {
@@ -236,98 +254,68 @@ fn trampoline(entry: usize, sp: [*]usize) noreturn {
 
 // TODO: make this be passed in from the build system
 const bin_path = "zig-out/bin/";
-fn getExePath(comptime name: []const u8) []const u8 {
+fn getTestExePath(comptime name: []const u8) []const u8 {
-    return bin_path ++ name;
+    return bin_path ++ "test_" ++ name;
 }
-const loader_path = getExePath("loader");
+const loader_path = bin_path ++ "loader";
 
-test "test_nolibc_nopie_exit" {
+test "nolibc_nopie_exit" {
-    try testExit("test_nolibc_nopie_exit");
+    try testHelper(&.{ loader_path, getTestExePath("nolibc_nopie_exit") }, "");
 }
-test "test_nolibc_pie_exit" {
+test "nolibc_pie_exit" {
-    try testExit("test_nolibc_pie_exit");
+    try testHelper(&.{ loader_path, getTestExePath("nolibc_pie_exit") }, "");
 }
-test "test_libc_pie_exit" {
+test "libc_pie_exit" {
-    try testExit("test_libc_pie_exit");
+    try testHelper(&.{ loader_path, getTestExePath("libc_pie_exit") }, "");
 }
 
-test "test_nolibc_nopie_helloWorld" {
+test "nolibc_nopie_helloWorld" {
-    try testHelloWorld("test_nolibc_nopie_helloWorld");
+    try testHelper(&.{ loader_path, getTestExePath("nolibc_nopie_helloWorld") }, "Hello World!\n");
 }
-test "test_nolibc_pie_helloWorld" {
+test "nolibc_pie_helloWorld" {
-    try testHelloWorld("test_nolibc_pie_helloWorld");
+    try testHelper(&.{ loader_path, getTestExePath("nolibc_pie_helloWorld") }, "Hello World!\n");
 }
-test "test_libc_pie_helloWorld" {
+test "libc_pie_helloWorld" {
-    try testHelloWorld("test_libc_pie_helloWorld");
+    try testHelper(&.{ loader_path, getTestExePath("libc_pie_helloWorld") }, "Hello World!\n");
 }
 
-test "test_nolibc_nopie_printArgs" {
+test "nolibc_nopie_printArgs" {
-    try testPrintArgs("test_nolibc_nopie_printArgs");
+    try testPrintArgs("nolibc_nopie_printArgs");
 }
-test "test_nolibc_pie_printArgs" {
+test "nolibc_pie_printArgs" {
-    try testPrintArgs("test_nolibc_pie_printArgs");
+    try testPrintArgs("nolibc_pie_printArgs");
 }
-test "test_libc_pie_printArgs" {
+test "libc_pie_printArgs" {
-    try testPrintArgs("test_libc_pie_printArgs");
+    try testPrintArgs("libc_pie_printArgs");
 }
 
-fn testExit(comptime name: []const u8) !void {
+test "echo" {
-    const exe_path = comptime getExePath(name);
+    try testHelper(&.{ "echo", "Hello", "There" }, "Hello There\n");
-    const argv = &.{ loader_path, exe_path };
-    log.info("Running test: {s}", .{name});
-
-    const result = try std.process.Child.run(.{
-        .allocator = testing.allocator,
-        .argv = argv,
-    });
-    defer testing.allocator.free(result.stdout);
-    defer testing.allocator.free(result.stderr);
-    errdefer std.log.err("term: {}", .{result.term});
-    errdefer std.log.err("stdout: {s}", .{result.stdout});
-
-    try testing.expectEqualStrings("", result.stdout);
-    try testing.expect(result.term == .Exited);
-    try testing.expectEqual(0, result.term.Exited);
-}
-
-fn testHelloWorld(comptime name: []const u8) !void {
-    const exe_path = comptime getExePath(name);
-    const argv = &.{ loader_path, exe_path };
-    log.info("Running test: {s}", .{name});
-
-    const result = try std.process.Child.run(.{
-        .allocator = testing.allocator,
-        .argv = argv,
-    });
-    defer testing.allocator.free(result.stdout);
-    defer testing.allocator.free(result.stderr);
-    errdefer std.log.err("term: {}", .{result.term});
-    errdefer std.log.err("stdout: {s}", .{result.stdout});
-
-    try testing.expectEqualStrings("Hello World!\n", result.stdout);
-    try testing.expect(result.term == .Exited);
-    try testing.expectEqual(0, result.term.Exited);
 }
 
 fn testPrintArgs(comptime name: []const u8) !void {
-    const exe_path = comptime getExePath(name);
+    const exe_path = getTestExePath(name);
-    const loader_argv: []const []const u8 = &.{ loader_path, exe_path, "foo", "bar", "baz", "hi" };
+    const loader_argv: []const []const u8 = &.{ loader_path, exe_path, "foo", "bar", "baz hi" };
     const target_argv = loader_argv[1..];
-    log.info("Running test: {s}", .{name});
+    const expected_stout = try mem.join(testing.allocator, " ", target_argv);
+    defer testing.allocator.free(expected_stout);
+    try testHelper(loader_argv, expected_stout);
+}
 
+fn testHelper(
+    argv: []const []const u8,
+    expected_stdout: []const u8,
+) !void {
     const result = try std.process.Child.run(.{
         .allocator = testing.allocator,
-        .argv = loader_argv,
+        .argv = argv,
     });
     defer testing.allocator.free(result.stdout);
     defer testing.allocator.free(result.stderr);
-    errdefer std.log.err("term: {}", .{result.term});
+    errdefer log(.err, "term: {}", .{result.term});
-    errdefer std.log.err("stdout: {s}", .{result.stdout});
+    errdefer log(.err, "stdout: {s}", .{result.stdout});
 
-    const expected_stout = try mem.join(testing.allocator, " ", target_argv);
+    try testing.expectEqualStrings(expected_stdout, result.stdout);
-    defer testing.allocator.free(expected_stout);
-
-    try testing.expectEqualStrings(expected_stout, result.stdout);
     try testing.expect(result.term == .Exited);
     try testing.expectEqual(0, result.term.Exited);
 }