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macho: do not write out ZEROFILL physically to file

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Prior to this change, `__DATA,__bss` and `__DATA,__thread_bss` would
get actually, physically written out to the output file, unnecessarily
filling the output file with 0s.
This commit is contained in:
Jakub Konka
2022-01-20 00:14:00 +01:00
committed by Andrew Kelley
parent dcbab17b62
commit 252fb642d5
1 changed files with 18 additions and 35 deletions
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53
src/link/MachO.zig
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@@ -867,17 +867,6 @@ pub fn flushModule(self: *MachO, comp: *Compilation) !void {
try self.parseDependentLibs(self.base.options.sysroot, &dependent_libs);
}
if (self.bss_section_index) |idx| {
const seg = &self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = &seg.sections.items[idx];
sect.offset = self.bss_file_offset;
}
if (self.tlv_bss_section_index) |idx| {
const seg = &self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = &seg.sections.items[idx];
sect.offset = self.tlv_bss_file_offset;
}
try self.createMhExecuteHeaderAtom();
for (self.objects.items) |*object, object_id| {
if (object.analyzed) continue;
@@ -964,19 +953,6 @@ pub fn flushModule(self: *MachO, comp: *Compilation) !void {
try self.writeAtoms();
}
if (self.bss_section_index) |idx| {
const seg = &self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = &seg.sections.items[idx];
self.bss_file_offset = sect.offset;
sect.offset = 0;
}
if (self.tlv_bss_section_index) |idx| {
const seg = &self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = &seg.sections.items[idx];
self.tlv_bss_file_offset = sect.offset;
sect.offset = 0;
}
try self.setEntryPoint();
try self.updateSectionOrdinals();
try self.writeLinkeditSegment();
@@ -2021,6 +1997,8 @@ fn writeAllAtoms(self: *MachO) !void {
const sect = seg.sections.items[match.sect];
var atom: *Atom = entry.value_ptr.*;
if (sect.flags == macho.S_ZEROFILL or sect.flags == macho.S_THREAD_LOCAL_ZEROFILL) continue;
var buffer = std.ArrayList(u8).init(self.base.allocator);
defer buffer.deinit();
try buffer.ensureTotalCapacity(try math.cast(usize, sect.size));
@@ -2073,6 +2051,8 @@ fn writeAtoms(self: *MachO) !void {
const sect = seg.sections.items[match.sect];
var atom: *Atom = entry.value_ptr.*;
if (sect.flags == macho.S_ZEROFILL or sect.flags == macho.S_THREAD_LOCAL_ZEROFILL) continue;
log.debug("writing atoms in {s},{s}", .{ sect.segName(), sect.sectName() });
while (atom.prev) |prev| {
@@ -4194,9 +4174,6 @@ fn populateMissingMetadata(self: *MachO) !void {
.flags = macho.S_THREAD_LOCAL_ZEROFILL,
},
);
const seg = self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = seg.sections.items[self.tlv_bss_section_index.?];
self.tlv_bss_file_offset = sect.offset;
}
if (self.bss_section_index == null) {
@@ -4211,9 +4188,6 @@ fn populateMissingMetadata(self: *MachO) !void {
.flags = macho.S_ZEROFILL,
},
);
const seg = self.load_commands.items[self.data_segment_cmd_index.?].segment;
const sect = seg.sections.items[self.bss_section_index.?];
self.bss_file_offset = sect.offset;
}
if (self.linkedit_segment_cmd_index == null) {
@@ -4513,9 +4487,10 @@ fn allocateSegment(self: *MachO, index: u16, offset: u64) !void {
// Allocate the sections according to their alignment at the beginning of the segment.
var start: u64 = offset;
for (seg.sections.items) |*sect, sect_id| {
const is_zerofill = sect.flags == macho.S_ZEROFILL or sect.flags == macho.S_THREAD_LOCAL_ZEROFILL;
const alignment = try math.powi(u32, 2, sect.@"align");
const start_aligned = mem.alignForwardGeneric(u64, start, alignment);
sect.offset = @intCast(u32, seg.inner.fileoff + start_aligned);
sect.offset = if (is_zerofill) 0 else @intCast(u32, seg.inner.fileoff + start_aligned);
sect.addr = seg.inner.vmaddr + start_aligned;
// Recalculate section size given the allocated start address
@@ -4542,11 +4517,15 @@ fn allocateSegment(self: *MachO, index: u16, offset: u64) !void {
} else 0;
start = start_aligned + sect.size;
if (!is_zerofill) {
seg.inner.filesize = start;
}
seg.inner.vmsize = start;
}
const seg_size_aligned = mem.alignForwardGeneric(u64, start, self.page_size);
seg.inner.filesize = seg_size_aligned;
seg.inner.vmsize = seg_size_aligned;
seg.inner.filesize = mem.alignForwardGeneric(u64, seg.inner.filesize, self.page_size);
seg.inner.vmsize = mem.alignForwardGeneric(u64, seg.inner.vmsize, self.page_size);
}
const InitSectionOpts = struct {
@@ -4584,8 +4563,12 @@ fn initSection(
off,
off + size,
});
sect.addr = seg.inner.vmaddr + off - seg.inner.fileoff;
sect.offset = @intCast(u32, off);
if (opts.flags != macho.S_ZEROFILL and opts.flags != macho.S_THREAD_LOCAL_ZEROFILL) {
sect.offset = @intCast(u32, off);
}
}
const index = @intCast(u16, seg.sections.items.len);