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link: avoid passing bad ptrs to pwritev

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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.
This commit is contained in:
Andrew Kelley 2022-07-26 20:05:54 -07:00
parent 0bc4726e00
commit ea3db3274d
2 changed files with 48 additions and 31 deletions
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75
src/link/C.zig
View File

@ -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;

4
src/link/Dwarf.zig
View File

@ -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;