zig

commit ea3db3274d890b7d00c907c037ffe203f41adbd3 (tree)
parent 0bc4726e00e794be9848b4b42dba43a0c7f4558e
Author: Andrew Kelley <andrew@ziglang.org>
Date:   Tue, 26 Jul 2022 20:05:54 -0700

link: avoid passing bad ptrs to pwritev

At least on Linux, the pwritev syscall checks the pointer and returns
EFAULT before it checks if the length is nonzero.

Perhaps this should be fixed in the standard library, however, these are
still improvements since they make the kernel do less work within the
syscall.

Diffstat:
M
src/link/C.zig
 | 
75
++++++++++++++++++++++++++++++++++++++++++++++-----------------------------
M
src/link/Dwarf.zig
 | 
4
++--

2 files changed, 48 insertions(+), 31 deletions(-)
diff --git a/src/link/C.zig b/src/link/C.zig
@@ -263,11 +263,13 @@ pub fn flushModule(self: *C, comp: *Compilation, prog_node: *std.Progress.Node) 
     // Covers zig.h and err_typedef_item.
     try f.all_buffers.ensureUnusedCapacity(gpa, 2);
 
-    f.all_buffers.appendAssumeCapacity(.{
-        .iov_base = zig_h,
-        .iov_len = zig_h.len,
-    });
-    f.file_size += zig_h.len;
+    if (zig_h.len != 0) {
+        f.all_buffers.appendAssumeCapacity(.{
+            .iov_base = zig_h,
+            .iov_len = zig_h.len,
+        });
+        f.file_size += zig_h.len;
+    }
 
     const err_typedef_writer = f.err_typedef_buf.writer(gpa);
     const err_typedef_index = f.all_buffers.items.len;
@@ -301,11 +303,18 @@ pub fn flushModule(self: *C, comp: *Compilation, prog_node: *std.Progress.Node) 
         try flushDecl(self, &f, decl_index);
     }
 
-    f.all_buffers.items[err_typedef_index] = .{
-        .iov_base = f.err_typedef_buf.items.ptr,
-        .iov_len = f.err_typedef_buf.items.len,
-    };
-    f.file_size += f.err_typedef_buf.items.len;
+    if (f.err_typedef_buf.items.len == 0) {
+        f.all_buffers.items[err_typedef_index] = .{
+            .iov_base = "",
+            .iov_len = 0,
+        };
+    } else {
+        f.all_buffers.items[err_typedef_index] = .{
+            .iov_base = f.err_typedef_buf.items.ptr,
+            .iov_len = f.err_typedef_buf.items.len,
+        };
+        f.file_size += f.err_typedef_buf.items.len;
+    }
 
     // Now the function bodies.
     try f.all_buffers.ensureUnusedCapacity(gpa, f.fn_count);
@@ -391,21 +400,25 @@ fn flushDecl(self: *C, f: *Flush, decl_index: Module.Decl.Index) FlushDeclError!
 
     if (decl_block.fwd_decl.items.len != 0) {
         const buf = decl_block.fwd_decl.items;
-        try f.all_buffers.append(gpa, .{
-            .iov_base = buf.ptr,
-            .iov_len = buf.len,
-        });
-        f.file_size += buf.len;
+        if (buf.len != 0) {
+            try f.all_buffers.append(gpa, .{
+                .iov_base = buf.ptr,
+                .iov_len = buf.len,
+            });
+            f.file_size += buf.len;
+        }
     }
     if (decl.getFunction() != null) {
         f.fn_count += 1;
     } else if (decl_block.code.items.len != 0) {
         const buf = decl_block.code.items;
-        try f.all_buffers.append(gpa, .{
-            .iov_base = buf.ptr,
-            .iov_len = buf.len,
-        });
-        f.file_size += buf.len;
+        if (buf.len != 0) {
+            try f.all_buffers.append(gpa, .{
+                .iov_base = buf.ptr,
+                .iov_len = buf.len,
+            });
+            f.file_size += buf.len;
+        }
     }
 }
 
@@ -421,19 +434,23 @@ pub fn flushEmitH(module: *Module) !void {
     defer all_buffers.deinit();
 
     var file_size: u64 = zig_h.len;
-    all_buffers.appendAssumeCapacity(.{
-        .iov_base = zig_h,
-        .iov_len = zig_h.len,
-    });
+    if (zig_h.len != 0) {
+        all_buffers.appendAssumeCapacity(.{
+            .iov_base = zig_h,
+            .iov_len = zig_h.len,
+        });
+    }
 
     for (emit_h.decl_table.keys()) |decl_index| {
         const decl_emit_h = emit_h.declPtr(decl_index);
         const buf = decl_emit_h.fwd_decl.items;
-        all_buffers.appendAssumeCapacity(.{
-            .iov_base = buf.ptr,
-            .iov_len = buf.len,
-        });
-        file_size += buf.len;
+        if (buf.len != 0) {
+            all_buffers.appendAssumeCapacity(.{
+                .iov_base = buf.ptr,
+                .iov_len = buf.len,
+            });
+            file_size += buf.len;
+        }
     }
 
     const directory = emit_h.loc.directory orelse module.comp.local_cache_directory;
diff --git a/src/link/Dwarf.zig b/src/link/Dwarf.zig
@@ -1752,7 +1752,7 @@ fn pwriteDbgLineNops(
         .iov_base = buf.ptr,
         .iov_len = buf.len,
     };
-    vec_index += 1;
+    if (buf.len > 0) vec_index += 1;
 
     {
         var padding_left = next_padding_size;
@@ -1861,7 +1861,7 @@ fn pwriteDbgInfoNops(
         .iov_base = buf.ptr,
         .iov_len = buf.len,
     };
-    vec_index += 1;
+    if (buf.len > 0) vec_index += 1;
 
     {
         var padding_left = next_padding_size;