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Fixed wrong calculation of locals size when parsing a wasm binary

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The fix involves moving the function leb128Decode over to parser. To me
it makes more sense for the function to belong in that module so I think
of it as a positive change. However I do not think that returning two
values is really necessary. I think a proper solution would be either
to parse the code or wrap the stream so we can count how many bytes are
readed. Therefore we could use std.leb.readUleb128 which should be less
error-prone.
This commit is contained in:
Ernesto Lanchares 2025-03-13 22:51:56 +00:00 • committed by Lorenzo Torres
parent 1c3f9702af
commit 2818fd14c5
2 changed files with 53 additions and 37 deletions
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35
src/vm/vm.zig
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@ -4,37 +4,10 @@ const Parser = @import("parse.zig");
const Allocator = std.mem.Allocator;
const AllocationError = error{OutOfMemory};
pub fn leb128Decode(comptime T: type, bytes: []u8) struct { len: usize, val: T } {
switch (@typeInfo(T)) {
.int => {},
else => @compileError("LEB128 integer decoding only support integers, but got " ++ @typeName(T)),
}
if (@typeInfo(T).int.bits != 32 and @typeInfo(T).int.bits != 64) {
@compileError("LEB128 integer decoding only supports 32 or 64 bits integers but got " ++ std.fmt.comptimePrint("{d} bits", .{@typeInfo(T).int.bits}));
}
var result: T = 0;
// TODO: is the type of shift important. Reading Wikipedia (not very much tho) it seems like we can use u32 and call it a day...
var shift: if (@typeInfo(T).int.bits == 32) u5 else u6 = 0;
var byte: u8 = undefined;
var len: usize = 0;
for (bytes) |b| {
len += 1;
result |= @as(T, @intCast((b & 0x7f))) << shift;
if ((b & (0x1 << 7)) == 0) {
byte = b;
break;
}
shift += 7;
}
if (@typeInfo(T).int.signedness == .signed) {
const size = @sizeOf(T) * 8;
if (shift < size and (byte & 0x40) != 0) {
result |= (~@as(T, 0) << shift);
}
}
return .{ .len = len, .val = result };
fn leb128Decode(comptime T: type, bytes: []u8) Parser.leb128Result(T) {
var fbs = std.io.fixedBufferStream(bytes);
// TODO: this catch should be unrecheable
return Parser.leb128Decode(T, fbs.reader()) catch .{ .len = 0, .val = 0 };
}
pub fn decodeLittleEndian(comptime T: type, bytes: []u8) T {