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objcopy: use defined data for padding ELF sections

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Seems the right thing to do, but not strictly necessary.
This commit is contained in:
Xavier Bouchoux
2023-03-12 11:08:06 +01:00
parent 7ab48163ee
commit b014ffc74f
1 changed files with 56 additions and 5 deletions
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61
src/objcopy.zig
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@@ -924,7 +924,7 @@ const ElfContents = struct {
// - unused sections are removed
// when emitting the debug file:
// - all sections are kept, but some are emptied and their types is changed to SHT_NOBITS
// the program header is kept unchanged. (`strip` does update it, but `eu-strip` does not, and it still works) TODO: maybe it can be omitted altogether from debug?
// the program header is kept unchanged. (`strip` does update it, but `eu-strip` does not, and it still works)
const Update = struct {
action: enum { keep, strip, empty },
@@ -1021,6 +1021,7 @@ const ElfContents = struct {
eof_offset = @sizeOf(elf.Elf64_Ehdr);
// program header as-is.
// nb: for only-debug files, removing it appears to work, but is invalid by ELF specifcation.
{
std.debug.assert(updated_elf_header.e_phoff == @sizeOf(elf.Elf64_Ehdr));
const data = std.mem.sliceAsBytes(self.program_segments);
@@ -1164,10 +1165,60 @@ const ElfContents = struct {
cmdbuf.appendAssumeCapacity(.{ .write_data = .{ .data = data, .out_offset = updated_elf_header.e_shoff } });
}
// write the target files
// TODO: pack together contiguous copies (cmdbuf is ordered, by construction)
// TODO: fill the paddings with zero or copy from source file
for (cmdbuf.items) |cmd| {
// consolidate holes between writes:
// by coping original padding data from in_file (by fusing contiguous ranges)
// by writing zeroes otherwise
const zeroes = [1]u8{0} ** 4096;
const consolidated_cmdbuf = blk: {
var newbuf = std.ArrayList(WriteCmd).init(allocator);
try newbuf.ensureUnusedCapacity(cmdbuf.items.len * 2);
var offset: u64 = 0;
var fused_cmd: ?WriteCmd = null;
for (cmdbuf.items) |cmd| {
switch (cmd) {
.write_data => |data| {
std.debug.assert(data.out_offset >= offset);
if (fused_cmd) |prev| {
newbuf.appendAssumeCapacity(prev);
fused_cmd = null;
}
if (data.out_offset > offset) {
newbuf.appendAssumeCapacity(.{ .write_data = .{ .data = zeroes[0 .. @intCast(usize, data.out_offset - offset)], .out_offset = offset } });
}
newbuf.appendAssumeCapacity(cmd);
offset = data.out_offset + data.data.len;
},
.copy_range => |range| {
std.debug.assert(range.out_offset >= offset);
if (fused_cmd) |prev| {
if (range.in_offset >= prev.copy_range.in_offset + prev.copy_range.len and (range.out_offset - prev.copy_range.out_offset == range.in_offset - prev.copy_range.in_offset)) {
fused_cmd = .{ .copy_range = .{
.in_offset = prev.copy_range.in_offset,
.out_offset = prev.copy_range.out_offset,
.len = (range.out_offset + range.len) - prev.copy_range.out_offset,
} };
} else {
newbuf.appendAssumeCapacity(prev);
if (range.out_offset > offset) {
newbuf.appendAssumeCapacity(.{ .write_data = .{ .data = zeroes[0 .. @intCast(usize, range.out_offset - offset)], .out_offset = offset } });
}
fused_cmd = cmd;
}
} else {
fused_cmd = cmd;
}
offset = range.out_offset + range.len;
},
}
}
if (fused_cmd) |cmd| {
newbuf.appendAssumeCapacity(cmd);
}
break :blk newbuf.items;
};
// write the output file
for (consolidated_cmdbuf) |cmd| {
switch (cmd) {
.write_data => |data| {
var iovec = [_]std.os.iovec_const{.{ .iov_base = data.data.ptr, .iov_len = data.data.len }};