Mystery syntax error on file suspiciously near 65536 bytes in size

[sunfishcode]

My branch here:

https://github.com/WebAssembly/spec/tree/large-file-syntax-error

has a (work-in-progress) test in test/float64.wasm. It currently fails mysteriously with

test/float64.wasm:524.130-524.130: syntax error

Line 524 is syntactically correct. Deleting seemingly any single the assert line from the file makes the syntax error go away. Suspiciously, the file size is just over 65536 bytes.

Anyone have any clues as to what could be going on here?

[sunfishcode]

Suspiciously, strace shows this:

read(3, "(module\n (func $add (param $x f"..., 65536) = 65536
close(3) = 0

[sunfishcode]

It appears to be a bug in the way files are read. #73 is a PR which fixes it.