Commit ea3db3274d890b7d00c907c037ffe203f41adbd3 | zig

author	Andrew Kelley <andrew@ziglang.org> 2022-07-26 20:05:54-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2022-07-26 20:05:54-07:00
log	ea3db3274d890b7d00c907c037ffe203f41adbd3
tree	eb21fc1c8c8edbdedc37c4913f8d88f97f090310
parent	0bc4726e00e794be9848b4b42dba43a0c7f4558e

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.

2 files changed, 48 insertions(+), 31 deletions(-)

src
- link
  - C.zig
  - Dwarf.zig

src/link/C.zig+46-29

 @@ -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(.{
+    if (zig_h.len != 0) {
-        .iov_base = zig_h,
+        f.all_buffers.appendAssumeCapacity(.{
-        .iov_len = zig_h.len,
+            .iov_base = zig_h,
-    });
+            .iov_len = zig_h.len,
-    f.file_size += 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] = .{
+    if (f.err_typedef_buf.items.len == 0) {
-        .iov_base = f.err_typedef_buf.items.ptr,
+        f.all_buffers.items[err_typedef_index] = .{
-        .iov_len = f.err_typedef_buf.items.len,
+            .iov_base = "",
-    };
+            .iov_len = 0,
-    f.file_size += f.err_typedef_buf.items.len;
+        };
+    } 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, .{
+        if (buf.len != 0) {
-            .iov_base = buf.ptr,
+            try f.all_buffers.append(gpa, .{
-            .iov_len = buf.len,
+                .iov_base = buf.ptr,
-        });
+                .iov_len = buf.len,
-        f.file_size += 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, .{
+        if (buf.len != 0) {
-            .iov_base = buf.ptr,
+            try f.all_buffers.append(gpa, .{
-            .iov_len = buf.len,
+                .iov_base = buf.ptr,
-        });
+                .iov_len = buf.len,
-        f.file_size += 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(.{
+    if (zig_h.len != 0) {
-        .iov_base = zig_h,
+        all_buffers.appendAssumeCapacity(.{
-        .iov_len = zig_h.len,
+            .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(.{
+        if (buf.len != 0) {
-            .iov_base = buf.ptr,
+            all_buffers.appendAssumeCapacity(.{
-            .iov_len = buf.len,
+                .iov_base = buf.ptr,
-        });
+                .iov_len = buf.len,
-        file_size += buf.len;
+            });
+            file_size += buf.len;
+        }
     }
     const directory = emit_h.loc.directory orelse module.comp.local_cache_directory;

src/link/Dwarf.zig+2-2

...	@@ -1752,7 +1752,7 @@ fn pwriteDbgLineNops(	...	@@ -1752,7 +1752,7 @@ fn pwriteDbgLineNops(
1752	.iov_base = buf.ptr,	1752	.iov_base = buf.ptr,
1753	.iov_len = buf.len,	1753	.iov_len = buf.len,
1754	};	1754	};
1755	vec_index += 1;	1755	if (buf.len > 0) vec_index += 1;
1756		1756
1757	{	1757	{
1758	var padding_left = next_padding_size;	1758	var padding_left = next_padding_size;
...	@@ -1861,7 +1861,7 @@ fn pwriteDbgInfoNops(	...	@@ -1861,7 +1861,7 @@ fn pwriteDbgInfoNops(
1861	.iov_base = buf.ptr,	1861	.iov_base = buf.ptr,
1862	.iov_len = buf.len,	1862	.iov_len = buf.len,
1863	};	1863	};
1864	vec_index += 1;	1864	if (buf.len > 0) vec_index += 1;
1865		1865
1866	{	1866	{
1867	var padding_left = next_padding_size;	1867	var padding_left = next_padding_size;