On Tue, Apr 21, 2020 at 3:32 PM Xi Wang <xi.wang@xxxxxxxxx> wrote: > > On Tue, Apr 21, 2020 at 10:39 AM H. Peter Anvin <hpa@xxxxxxxxx> wrote: > > x32 is not x86-32. In Linux we generally call the latter "i386". > > Agreed. Most of the previous patches to this file use "x32" and this > one just wanted to be consistent. > > > C7 /0 imm32 is a valid instruction on i386. However, it is also > > inefficient when the destination is a register, because B8+r imm32 is > > equivalent, and when the value is zero, XOR is indeed more efficient. > > > > The real error is using EMIT3() instead of EMIT2_off32(), but XOR is > > more efficient. However, let's make the bug statement *correct*, or it > > is going to confuse the Hades out of people in the future. > > I don't see how the bug statement is incorrect, which merely points > out that "C7 C0 0" is an invalid instruction, regardless of whether > the JIT intended to emit C7 /0 imm32, B8+r imm32, 31 /r, 33 /r, or any > other equivalent form. You should explain the reason it is invalid, ie. the instruction encoding needs a 32-bit immediate but the current code only emits an 8-bit immediate. -- Brian Gerst
