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wasm-linker: emit 'data count' & segment flags

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When linking with shared-memory enabled, we must ensure to emit
the "data count" section as well as emit the correct segment flags
to tell the runtime/loader that each segment is passive. This is
required as we don't emit the offsets for such segments but instead
initialize each segment (for each thread) during runtime.
This commit is contained in:
Luuk de Gram 2023-03-14 19:31:45 +01:00
parent fb9d3cd50e
commit 00af3a79ae
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GPG Key ID: A8CFE58E4DC7D664
1 changed files with 49 additions and 5 deletions
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54
src/link/Wasm.zig
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@ -180,6 +180,16 @@ pub const Segment = struct {
alignment: u32,
size: u32,
offset: u32,
flags: u32,
pub const Flag = enum(u32) {
WASM_DATA_SEGMENT_IS_PASSIVE = 0x01,
WASM_DATA_SEGMENT_HAS_MEMINDEX = 0x02,
};
pub fn isPassive(segment: Segment) bool {
return segment.flags & @enumToInt(Flag.WASM_DATA_SEGMENT_IS_PASSIVE) != 0;
}
};
pub const Export = struct {
@ -1673,6 +1683,7 @@ fn parseAtom(wasm: *Wasm, atom_index: Atom.Index, kind: Kind) !void {
.alignment = atom.alignment,
.size = atom.size,
.offset = 0,
.flags = 0,
});
}
@ -1711,10 +1722,15 @@ fn parseAtom(wasm: *Wasm, atom_index: Atom.Index, kind: Kind) !void {
break :result index;
} else {
const index = @intCast(u32, wasm.segments.items.len);
var flags: u32 = 0;
if (wasm.base.options.shared_memory) {
flags |= @enumToInt(Segment.Flag.WASM_DATA_SEGMENT_IS_PASSIVE);
}
try wasm.segments.append(wasm.base.allocator, .{
.alignment = atom.alignment,
.size = 0,
.offset = 0,
.flags = flags,
});
gop.value_ptr.* = index;
@ -2365,7 +2381,16 @@ pub fn getMatchingSegment(wasm: *Wasm, object_index: u16, relocatable_index: u32
const result = try wasm.data_segments.getOrPut(wasm.base.allocator, segment_info.outputName(merge_segment));
if (!result.found_existing) {
result.value_ptr.* = index;
try wasm.appendDummySegment();
var flags: u32 = 0;
if (wasm.base.options.shared_memory) {
flags |= @enumToInt(Segment.Flag.WASM_DATA_SEGMENT_IS_PASSIVE);
}
try wasm.segments.append(wasm.base.allocator, .{
.alignment = 1,
.size = 0,
.offset = 0,
.flags = flags,
});
return index;
} else return result.value_ptr.*;
},
@ -2439,6 +2464,7 @@ fn appendDummySegment(wasm: *Wasm) !void {
.alignment = 1,
.size = 0,
.offset = 0,
.flags = 0,
});
}
@ -3147,6 +3173,19 @@ fn writeToFile(
section_count += 1;
}
// When the shared-memory option is enabled, we *must* emit the 'data count' section.
const data_segments_count = wasm.data_segments.count() - @boolToInt(wasm.data_segments.contains(".bss") and import_memory);
if (data_segments_count != 0 and wasm.base.options.shared_memory) {
const header_offset = try reserveVecSectionHeader(&binary_bytes);
try writeVecSectionHeader(
binary_bytes.items,
header_offset,
.data_count,
@intCast(u32, binary_bytes.items.len - header_offset - header_size),
@intCast(u32, data_segments_count),
);
}
// Code section
var code_section_size: u32 = 0;
if (wasm.code_section_index) |code_index| {
@ -3197,7 +3236,7 @@ fn writeToFile(
}
// Data section
if (wasm.data_segments.count() != 0) {
if (data_segments_count != 0) {
const header_offset = try reserveVecSectionHeader(&binary_bytes);
var it = wasm.data_segments.iterator();
@ -3212,10 +3251,15 @@ fn writeToFile(
segment_count += 1;
var atom_index = wasm.atoms.get(segment_index).?;
// flag and index to memory section (currently, there can only be 1 memory section in wasm)
try leb.writeULEB128(binary_writer, @as(u32, 0));
try leb.writeULEB128(binary_writer, segment.flags);
if (segment.flags & @enumToInt(Wasm.Segment.Flag.WASM_DATA_SEGMENT_HAS_MEMINDEX) != 0) {
try leb.writeULEB128(binary_writer, @as(u32, 0)); // memory is always index 0 as we only have 1 memory entry
}
// when a segment is passive, it's initialized during runtime.
if (!segment.isPassive()) {
try emitInit(binary_writer, .{ .i32_const = @bitCast(i32, segment.offset) });
}
// offset into data section
try emitInit(binary_writer, .{ .i32_const = @bitCast(i32, segment.offset) });
try leb.writeULEB128(binary_writer, segment.size);
// fill in the offset table and the data segments