Rewrite FixedBufferAllocator. Simplify code, documenting behavior better. Fix a bug where a very large allocation could overflow a usize, causing a false positive allocation. Provide limited comptime allocator support.

Author: RetroDev256

lib/compiler/aro/aro/Driver/Filesystem.zig

@@ -23,10 +23,11 @@ fn findProgramByNameFake(entries: []const Filesystem.Entry, name: []const u8, pa
     }
     const path_env = path orelse return null;
     var fib = std.heap.FixedBufferAllocator.init(buf);
+    const fib_initial_state = fib.savestate();
 
     var it = mem.tokenizeScalar(u8, path_env, std.fs.path.delimiter);
     while (it.next()) |path_dir| {
-        defer fib.reset();
+        defer fib.restore(fib_initial_state);
         const full_path = std.fs.path.join(fib.allocator(), &.{ path_dir, name }) catch continue;
         if (canExecuteFake(entries, full_path)) return full_path;
     }
@@ -84,10 +85,11 @@ fn findProgramByNamePosix(name: []const u8, path: ?[]const u8, buf: []u8) ?[]con
     }
     const path_env = path orelse return null;
     var fib = std.heap.FixedBufferAllocator.init(buf);
+    const fib_initial_state = fib.savestate();
 
     var it = mem.tokenizeScalar(u8, path_env, std.fs.path.delimiter);
     while (it.next()) |path_dir| {
-        defer fib.reset();
+        defer fib.restore(fib_initial_state);
         const full_path = std.fs.path.join(fib.allocator(), &.{ path_dir, name }) catch continue;
         if (canExecutePosix(full_path)) return full_path;
     }

lib/compiler/aro/aro/Toolchain.zig

@@ -216,14 +216,15 @@ pub fn addFilePathLibArgs(tc: *const Toolchain, argv: *std.ArrayList([]const u8)
 fn getProgramPath(tc: *const Toolchain, name: []const u8, buf: []u8) []const u8 {
     var path_buf: [std.fs.max_path_bytes]u8 = undefined;
     var fib = std.heap.FixedBufferAllocator.init(&path_buf);
+    const fib_initial_state = fib.savestate();
 
     var tool_specific_buf: [64]u8 = undefined;
     var possible_name_buf: [2][]const u8 = undefined;
     const possible_names = possibleProgramNames(tc.driver.raw_target_triple, name, &tool_specific_buf, &possible_name_buf);
 
     for (possible_names) |tool_name| {
         for (tc.program_paths.items) |program_path| {
-            defer fib.reset();
+            defer fib.restore(fib_initial_state);
 
             const candidate = std.fs.path.join(fib.allocator(), &.{ program_path, tool_name }) catch continue;
 

lib/compiler/test_runner.zig

@@ -37,6 +37,7 @@ pub fn main() void {
         return mainSimple() catch @panic("test failure\n");
     }
 
+    const fba_initial_state = fba.savestate();
     const args = std.process.argsAlloc(fba.allocator()) catch
         @panic("unable to parse command line args");
 
@@ -61,7 +62,7 @@ pub fn main() void {
         fuzz_abi.fuzzer_init(.fromSlice(cache_dir));
     }
 
-    fba.reset();
+    fba.restore(fba_initial_state);
 
     if (listen) {
         return mainServer() catch @panic("internal test runner failure");

lib/std/heap.zig

@@ -442,7 +442,7 @@ pub fn StackFallbackAllocator(comptime size: usize) type {
             ra: usize,
         ) bool {
             const self: *Self = @ptrCast(@alignCast(ctx));
-            if (self.fixed_buffer_allocator.ownsPtr(buf.ptr)) {
+            if (mem.sliceOwnsPtr(u8, &self.buffer, @ptrCast(buf.ptr))) {
                 return FixedBufferAllocator.resize(&self.fixed_buffer_allocator, buf, alignment, new_len, ra);
             } else {
                 return self.fallback_allocator.rawResize(buf, alignment, new_len, ra);
@@ -457,7 +457,7 @@ pub fn StackFallbackAllocator(comptime size: usize) type {
             return_address: usize,
         ) ?[*]u8 {
             const self: *Self = @ptrCast(@alignCast(context));
-            if (self.fixed_buffer_allocator.ownsPtr(memory.ptr)) {
+            if (mem.sliceOwnsPtr(u8, &self.buffer, @ptrCast(memory.ptr))) {
                 return FixedBufferAllocator.remap(&self.fixed_buffer_allocator, memory, alignment, new_len, return_address);
             } else {
                 return self.fallback_allocator.rawRemap(memory, alignment, new_len, return_address);
@@ -471,7 +471,7 @@ pub fn StackFallbackAllocator(comptime size: usize) type {
             ra: usize,
         ) void {
             const self: *Self = @ptrCast(@alignCast(ctx));
-            if (self.fixed_buffer_allocator.ownsPtr(buf.ptr)) {
+            if (mem.sliceOwnsPtr(u8, &self.buffer, @ptrCast(buf.ptr))) {
                 return FixedBufferAllocator.free(&self.fixed_buffer_allocator, buf, alignment, ra);
             } else {
                 return self.fallback_allocator.rawFree(buf, alignment, ra);