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macho: create dummy atom of size 0 marking end of a section

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Some compilers such as Go reference the end of a section (addr + size)
which cannot be contained in any non-zero atom (since then this atom
would exceed section boundaries). In order to facilitate this behaviour,
we create a dummy zero-sized atom at section end (addr + size).
This commit is contained in:
Jakub Konka 2024-10-12 00:04:33 +02:00 committed by Andrew Kelley
parent 008acd0547
commit 7e530c13b3
1 changed files with 34 additions and 3 deletions
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37
src/link/MachO/Object.zig
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@ -308,7 +308,7 @@ fn initSubsections(self: *Object, allocator: Allocator, nlists: anytype) !void {
} else nlists.len;
if (nlist_start == nlist_end or nlists[nlist_start].nlist.n_value > sect.addr) {
const name = try std.fmt.allocPrintZ(allocator, "{s}${s}", .{ sect.segName(), sect.sectName() });
const name = try std.fmt.allocPrintZ(allocator, "{s}${s}$begin", .{ sect.segName(), sect.sectName() });
defer allocator.free(name);
const size = if (nlist_start == nlist_end) sect.size else nlists[nlist_start].nlist.n_value - sect.addr;
const atom_index = try self.addAtom(allocator, .{
@ -359,6 +359,25 @@ fn initSubsections(self: *Object, allocator: Allocator, nlists: anytype) !void {
self.symtab.items(.size)[nlists[i].idx] = size;
}
}
// Some compilers such as Go reference the end of a section (addr + size)
// which cannot be contained in any non-zero atom (since then this atom
// would exceed section boundaries). In order to facilitate this behaviour,
// we create a dummy zero-sized atom at section end (addr + size).
const name = try std.fmt.allocPrintZ(allocator, "{s}${s}$end", .{ sect.segName(), sect.sectName() });
defer allocator.free(name);
const atom_index = try self.addAtom(allocator, .{
.name = try self.addString(allocator, name),
.n_sect = @intCast(n_sect),
.off = sect.size,
.size = 0,
.alignment = sect.@"align",
});
try self.atoms_indexes.append(allocator, atom_index);
try subsections.append(allocator, .{
.atom = atom_index,
.off = sect.size,
});
}
}
@ -743,7 +762,7 @@ pub fn findAtom(self: Object, addr: u64) ?Atom.Index {
const slice = self.sections.slice();
for (slice.items(.header), slice.items(.subsections), 0..) |sect, subs, n_sect| {
if (subs.items.len == 0) continue;
if (sect.addr == addr) return subs.items[0].atom;
if (addr == sect.addr) return subs.items[0].atom;
if (sect.addr < addr and addr < sect.addr + sect.size) {
return self.findAtomInSection(addr, @intCast(n_sect));
}
@ -794,7 +813,19 @@ fn linkNlistToAtom(self: *Object, macho_file: *MachO) !void {
defer tracy.end();
for (self.symtab.items(.nlist), self.symtab.items(.atom)) |nlist, *atom| {
if (!nlist.stab() and nlist.sect()) {
if (self.findAtomInSection(nlist.n_value, nlist.n_sect - 1)) |atom_index| {
const sect = self.sections.items(.header)[nlist.n_sect - 1];
const subs = self.sections.items(.subsections)[nlist.n_sect - 1].items;
if (nlist.n_value == sect.addr) {
// If the nlist address is the start of the section, return the first atom
// since it is guaranteed to always start at section's start address.
atom.* = subs[0].atom;
} else if (nlist.n_value == sect.addr + sect.size) {
// If the nlist address matches section's boundary (address + size),
// return the last atom since it is guaranteed to always point
// at the section's end boundary.
atom.* = subs[subs.len - 1].atom;
} else if (self.findAtomInSection(nlist.n_value, nlist.n_sect - 1)) |atom_index| {
// In all other cases, do a binary search to find a matching atom for the symbol.
atom.* = atom_index;
} else {
try macho_file.reportParseError2(self.index, "symbol {s} not attached to any (sub)section", .{