Merge pull request #11919 from squeek502/failing-allocator-stacktrace

Add stack trace capturing to `FailingAllocator` and use it to improve `checkAllAllocationFailures`

lib/std/debug.zig

@@ -26,6 +26,27 @@ pub const runtime_safety = switch (builtin.mode) {
     .ReleaseFast, .ReleaseSmall => false,
 };
 
+pub const sys_can_stack_trace = switch (builtin.cpu.arch) {
+    // Observed to go into an infinite loop.
+    // TODO: Make this work.
+    .mips,
+    .mipsel,
+    => false,
+
+    // `@returnAddress()` in LLVM 10 gives
+    // "Non-Emscripten WebAssembly hasn't implemented __builtin_return_address".
+    .wasm32,
+    .wasm64,
+    => builtin.os.tag == .emscripten,
+
+    // `@returnAddress()` is unsupported in LLVM 13.
+    .bpfel,
+    .bpfeb,
+    => false,
+
+    else => true,
+};
+
 pub const LineInfo = struct {
     line: u64,
     column: u64,

lib/std/heap/general_purpose_allocator.zig

@@ -105,28 +105,8 @@ const StackTrace = std.builtin.StackTrace;
 /// Integer type for pointing to slots in a small allocation
 const SlotIndex = std.meta.Int(.unsigned, math.log2(page_size) + 1);
 
-const sys_can_stack_trace = switch (builtin.cpu.arch) {
-    // Observed to go into an infinite loop.
-    // TODO: Make this work.
-    .mips,
-    .mipsel,
-    => false,
-
-    // `@returnAddress()` in LLVM 10 gives
-    // "Non-Emscripten WebAssembly hasn't implemented __builtin_return_address".
-    .wasm32,
-    .wasm64,
-    => builtin.os.tag == .emscripten,
-
-    // `@returnAddress()` is unsupported in LLVM 13.
-    .bpfel,
-    .bpfeb,
-    => false,
-
-    else => true,
-};
 const default_test_stack_trace_frames: usize = if (builtin.is_test) 8 else 4;
-const default_sys_stack_trace_frames: usize = if (sys_can_stack_trace) default_test_stack_trace_frames else 0;
+const default_sys_stack_trace_frames: usize = if (std.debug.sys_can_stack_trace) default_test_stack_trace_frames else 0;
 const default_stack_trace_frames: usize = switch (builtin.mode) {
     .Debug => default_sys_stack_trace_frames,
     else => 0,

lib/std/testing.zig

@@ -534,18 +534,27 @@ test {
 ///
 /// Any relevant state shared between runs of `test_fn` *must* be reset within `test_fn`.
 ///
-/// Expects that the `test_fn` has a deterministic number of memory allocations
-/// (an error will be returned if non-deterministic allocations are detected).
-///
 /// The strategy employed is to:
 /// - Run the test function once to get the total number of allocations.
 /// - Then, iterate and run the function X more times, incrementing
 ///   the failing index each iteration (where X is the total number of
 ///   allocations determined previously)
 ///
+/// Expects that `test_fn` has a deterministic number of memory allocations:
+/// - If an allocation was made to fail during a run of `test_fn`, but `test_fn`
+///   didn't return `error.OutOfMemory`, then `error.SwallowedOutOfMemoryError`
+///   is returned from `checkAllAllocationFailures`. You may want to ignore this
+///   depending on whether or not the code you're testing includes some strategies
+///   for recovering from `error.OutOfMemory`.
+/// - If a run of `test_fn` with an expected allocation failure executes without
+///   an allocation failure being induced, then `error.NondeterministicMemoryUsage`
+///   is returned. This error means that there are allocation points that won't be
+///   tested by the strategy this function employs (that is, there are sometimes more
+///   points of allocation than the initial run of `test_fn` detects).
+///
 /// ---
 ///
-/// Here's an example of using a simple test case that will cause a leak when the
+/// Here's an example using a simple test case that will cause a leak when the
 /// allocation of `bar` fails (but will pass normally):
 ///
 /// ```zig
@@ -645,12 +654,16 @@ pub fn checkAllAllocationFailures(backing_allocator: std.mem.Allocator, comptime
         args.@"0" = failing_allocator_inst.allocator();
 
         if (@call(.{}, test_fn, args)) |_| {
-            return error.NondeterministicMemoryUsage;
+            if (failing_allocator_inst.has_induced_failure) {
+                return error.SwallowedOutOfMemoryError;
+            } else {
+                return error.NondeterministicMemoryUsage;
+            }
         } else |err| switch (err) {
             error.OutOfMemory => {
                 if (failing_allocator_inst.allocated_bytes != failing_allocator_inst.freed_bytes) {
                     print(
-                        "\nfail_index: {d}/{d}\nallocated bytes: {d}\nfreed bytes: {d}\nallocations: {d}\ndeallocations: {d}\n",
+                        "\nfail_index: {d}/{d}\nallocated bytes: {d}\nfreed bytes: {d}\nallocations: {d}\ndeallocations: {d}\nallocation that was made to fail: {s}",
                         .{
                             fail_index,
                             needed_alloc_count,
@@ -658,6 +671,7 @@ pub fn checkAllAllocationFailures(backing_allocator: std.mem.Allocator, comptime
                             failing_allocator_inst.freed_bytes,
                             failing_allocator_inst.allocations,
                             failing_allocator_inst.deallocations,
+                            failing_allocator_inst.getStackTrace(),
                         },
                     );
                     return error.MemoryLeakDetected;

lib/std/testing/failing_allocator.zig

@@ -19,6 +19,10 @@ pub const FailingAllocator = struct {
     freed_bytes: usize,
     allocations: usize,
     deallocations: usize,
+    stack_addresses: [num_stack_frames]usize,
+    has_induced_failure: bool,
+
+    const num_stack_frames = if (std.debug.sys_can_stack_trace) 16 else 0;
 
     /// `fail_index` is the number of successful allocations you can
     /// expect from this allocator. The next allocation will fail.
@@ -37,6 +41,8 @@ pub const FailingAllocator = struct {
             .freed_bytes = 0,
             .allocations = 0,
             .deallocations = 0,
+            .stack_addresses = undefined,
+            .has_induced_failure = false,
         };
     }
 
@@ -52,6 +58,15 @@ pub const FailingAllocator = struct {
         return_address: usize,
     ) error{OutOfMemory}![]u8 {
         if (self.index == self.fail_index) {
+            if (!self.has_induced_failure) {
+                mem.set(usize, &self.stack_addresses, 0);
+                var stack_trace = std.builtin.StackTrace{
+                    .instruction_addresses = &self.stack_addresses,
+                    .index = 0,
+                };
+                std.debug.captureStackTrace(return_address, &stack_trace);
+                self.has_induced_failure = true;
+            }
             return error.OutOfMemory;
         }
         const result = try self.internal_allocator.rawAlloc(len, ptr_align, len_align, return_address);
@@ -88,4 +103,17 @@ pub const FailingAllocator = struct {
         self.deallocations += 1;
         self.freed_bytes += old_mem.len;
     }
+
+    /// Only valid once `has_induced_failure == true`
+    pub fn getStackTrace(self: *FailingAllocator) std.builtin.StackTrace {
+        std.debug.assert(self.has_induced_failure);
+        var len: usize = 0;
+        while (len < self.stack_addresses.len and self.stack_addresses[len] != 0) {
+            len += 1;
+        }
+        return .{
+            .instruction_addresses = &self.stack_addresses,
+            .index = len,
+        };
+    }
 };