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wasm-linker: Prevent overalignment for segments

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Previously, the data segments were being aligned twice.
This caused us to overalign the segment and therefore allocate a much larger
size for each segment than was required. This fix ensures we align and set the size
just once, ensuring semantically correct binaries as well as smaller binaries.
This commit is contained in:
Luuk de Gram 2022-04-13 22:14:48 +02:00
parent cf37101108
commit d66c61a2cf
2 changed files with 7 additions and 15 deletions
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17
src/link/Wasm.zig
View File

@ -962,11 +962,6 @@ fn parseAtom(self: *Wasm, atom: *Atom, kind: Kind) !void {
const segment: *Segment = &self.segments.items[final_index];
segment.alignment = std.math.max(segment.alignment, atom.alignment);
segment.size = std.mem.alignForwardGeneric(
u32,
std.mem.alignForwardGeneric(u32, segment.size, atom.alignment) + atom.size,
segment.alignment,
);
if (self.atoms.getPtr(final_index)) |last| {
last.*.next = atom;
@ -978,9 +973,10 @@ fn parseAtom(self: *Wasm, atom: *Atom, kind: Kind) !void {
}
fn allocateAtoms(self: *Wasm) !void {
var it = self.atoms.valueIterator();
while (it.next()) |current_atom| {
var atom: *Atom = current_atom.*.getFirst();
var it = self.atoms.iterator();
while (it.next()) |entry| {
const segment = &self.segments.items[entry.key_ptr.*];
var atom: *Atom = entry.value_ptr.*.getFirst();
var offset: u32 = 0;
while (true) {
offset = std.mem.alignForwardGeneric(u32, offset, atom.alignment);
@ -996,6 +992,7 @@ fn allocateAtoms(self: *Wasm) !void {
self.symbol_atom.putAssumeCapacity(atom.symbolLoc(), atom); // Update atom pointers
atom = atom.next orelse break;
}
segment.size = std.mem.alignForwardGeneric(u32, offset, segment.alignment);
}
}
@ -1566,8 +1563,8 @@ pub fn flushModule(self: *Wasm, comp: *Compilation) !void {
try self.objects.items[object_index].parseIntoAtoms(self.base.allocator, object_index, self);
}
try self.setupMemory();
try self.allocateAtoms();
try self.setupMemory();
self.mapFunctionTable();
try self.mergeSections();
try self.mergeTypes();
@ -1832,7 +1829,7 @@ pub fn flushModule(self: *Wasm, comp: *Compilation) !void {
segment_count += 1;
const atom_index = entry.value_ptr.*;
var atom: *Atom = self.atoms.getPtr(atom_index).?.*.getFirst();
var segment = self.segments.items[atom_index];
const segment = self.segments.items[atom_index];
// flag and index to memory section (currently, there can only be 1 memory section in wasm)
try leb.writeULEB128(writer, @as(u32, 0));

5
src/link/Wasm/Object.zig
View File

@ -865,11 +865,6 @@ pub fn parseIntoAtoms(self: *Object, gpa: Allocator, object_index: u16, wasm_bin
const segment: *Wasm.Segment = &wasm_bin.segments.items[final_index];
segment.alignment = std.math.max(segment.alignment, atom.alignment);
segment.size = std.mem.alignForwardGeneric(
u32,
std.mem.alignForwardGeneric(u32, segment.size, atom.alignment) + atom.size,
segment.alignment,
);
if (wasm_bin.atoms.getPtr(final_index)) |last| {
last.*.next = atom;