[Qemu-devel] [Bug 1832281] Re: tcg bug master / 4.0.0 v8 operation >>> and |=

[Peter Maydell]

This might be the same underlying problem as LP:1815423 which also
mentions some issues with Javascript calculations involving arithmetic
operations on a js "undefined" value. That bug has a C-only reproduce
case so is probably a good place to start for anybody interesting in
investigating and fixing it.

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Title:
  tcg bug master / 4.0.0 v8 operation >>> and |=

Status in QEMU:
  New

Bug description:
  vm guest is linux, executed with tcg
  running this Node.js snippet leads to

  $ node
  > a = undefined
  undefined
  > a >>> 0
  4294967295

  host node
  $ node
  > a = undefined
  undefined
  > a >>> 0
  0

  same with |=

  node
  Welcome to Node.js v12.4.0.
  Type ".help" for more information.
  > let buffer
  undefined
  > buffer |= 0
  0

  vm with tcg:

  $ ./out/Release/node --version
  v12.4.0
  ./out/Release/node -e "let buffer; buffer |= 0; console.log(buffer);"
  -1

  vm guest is debian x86_64 latest release
  vm guest is started with ./x86_64-softmmu/qemu-system-x86_64 -vnc :0 -cdrom 
debian-9.9.0-amd64-netinst.iso -m 4G -smp cores=6,threads=1,sockets=1 -nic 
user,hostfwd=tcp:ipv4addr:2233-:22 -cpu qemu64 debian.img

  git tag v4.0.0 and master, commit
  a578cdfbdd8f9beff5ced52b7826ddb1669abbbf, for building qemu-system-
  x86_64 was used.

  Node.js is compiled on the vm guest (v12.4.0 / master)

  see also
  https://github.com/nodejs/node/issues/19348#issuecomment-500465502

  I need further assistance to track down the cause of the bug.

  Kind regards
  Manuel

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