Merge pull request #4408 from LemonBoy/mmap-i386-fix

handle SIGBUS, fix mmap on i386 linux

lib/std/debug.zig

@@ -2256,6 +2256,7 @@ pub fn attachSegfaultHandler() void {
 
     os.sigaction(os.SIGSEGV, &act, null);
     os.sigaction(os.SIGILL, &act, null);
+    os.sigaction(os.SIGBUS, &act, null);
 }
 
 fn resetSegfaultHandler() void {
@@ -2273,6 +2274,7 @@ fn resetSegfaultHandler() void {
     };
     os.sigaction(os.SIGSEGV, &act, null);
     os.sigaction(os.SIGILL, &act, null);
+    os.sigaction(os.SIGBUS, &act, null);
 }
 
 fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *const c_void) callconv(.C) noreturn {
@@ -2285,6 +2287,7 @@ fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *const c_vo
     switch (sig) {
         os.SIGSEGV => std.debug.warn("Segmentation fault at address 0x{x}\n", .{addr}),
         os.SIGILL => std.debug.warn("Illegal instruction at address 0x{x}\n", .{addr}),
+        os.SIGBUS => std.debug.warn("Bus error at address 0x{x}\n", .{addr}),
         else => unreachable,
     }
     switch (builtin.arch) {

lib/std/os/linux/i386.zig

@@ -72,11 +72,17 @@ pub fn syscall6(
     arg5: usize,
     arg6: usize,
 ) usize {
+    // The 6th argument is passed via memory as we're out of registers if ebp is
+    // used as frame pointer. We push arg6 value on the stack before changing
+    // ebp or esp as the compiler may reference it as an offset relative to one
+    // of those two registers.
     return asm volatile (
-        \\  push %%ebp
-        \\  mov %[arg6], %%ebp
-        \\  int $0x80
-        \\  pop %%ebp
+        \\ push %[arg6]
+        \\ push %%ebp
+        \\ mov  4(%%esp), %%ebp
+        \\ int  $0x80
+        \\ pop  %%ebp
+        \\ add  $4, %%esp
         : [ret] "={eax}" (-> usize)
         : [number] "{eax}" (number),
           [arg1] "{ebx}" (arg1),

lib/std/os/test.zig

@@ -256,3 +256,101 @@ test "memfd_create" {
     expect(bytes_read == 4);
     expect(mem.eql(u8, buf[0..4], "test"));
 }
+
+test "mmap" {
+    if (builtin.os == .windows)
+        return error.SkipZigTest;
+
+    // Simple mmap() call with non page-aligned size
+    {
+        const data = try os.mmap(
+            null,
+            1234,
+            os.PROT_READ | os.PROT_WRITE,
+            os.MAP_ANONYMOUS | os.MAP_PRIVATE,
+            -1,
+            0,
+        );
+        defer os.munmap(data);
+
+        testing.expectEqual(@as(usize, 1234), data.len);
+
+        // By definition the data returned by mmap is zero-filled
+        std.mem.set(u8, data[0 .. data.len - 1], 0x55);
+        testing.expect(mem.indexOfScalar(u8, data, 0).? == 1234 - 1);
+    }
+
+    const test_out_file = "os_tmp_test";
+    // Must be a multiple of 4096 so that the test works with mmap2
+    const alloc_size = 8 * 4096;
+
+    // Create a file used for testing mmap() calls with a file descriptor
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{});
+        defer file.close();
+
+        var out_stream = file.outStream();
+        const stream = &out_stream.stream;
+
+        var i: u32 = 0;
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            try stream.writeIntNative(u32, i);
+        }
+    }
+
+    // Map the whole file
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{
+            .read = true,
+            .truncate = false,
+        });
+        defer file.close();
+
+        const data = try os.mmap(
+            null,
+            alloc_size,
+            os.PROT_READ,
+            os.MAP_PRIVATE,
+            file.handle,
+            0,
+        );
+        defer os.munmap(data);
+
+        var mem_stream = io.SliceInStream.init(data);
+        const stream = &mem_stream.stream;
+
+        var i: u32 = 0;
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            testing.expectEqual(i, try stream.readIntNative(u32));
+        }
+    }
+
+    // Map the upper half of the file
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{
+            .read = true,
+            .truncate = false,
+        });
+        defer file.close();
+
+        const data = try os.mmap(
+            null,
+            alloc_size,
+            os.PROT_READ,
+            os.MAP_PRIVATE,
+            file.handle,
+            alloc_size / 2,
+        );
+        defer os.munmap(data);
+
+        var mem_stream = io.SliceInStream.init(data);
+        const stream = &mem_stream.stream;
+
+        var i: u32 = alloc_size / 2 / @sizeOf(u32);
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            testing.expectEqual(i, try stream.readIntNative(u32));
+        }
+    }
+
+    try fs.cwd().deleteFile(test_out_file);
+}