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LibJS+LibJIT: Don't turn patchable movs into xors with self

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If a mov instruction is meant to be patchable, we don't want to rewrite
it as a xor, since that removes the slot where we'd patch in the right
value later.

Also, make sure to set both size bits in the REX prefix for xoring a
register with itself.
This commit is contained in:
Andreas Kling 2023-10-26 19:48:37 +02:00
parent 8b32e98f3f
commit 5b198ccf32
2 changed files with 12 additions and 5 deletions
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11
Userland/Libraries/LibJIT/Assembler.h
View file

@ -108,7 +108,12 @@ struct Assembler {
emit8(count.offset_or_immediate); emit8(count.offset_or_immediate);
} }
void mov(Operand dst, Operand src) enum class Patchable {
Yes,
No,
};
void mov(Operand dst, Operand src, Patchable patchable = Patchable::No)
{ {
if (dst.type == Operand::Type::Reg && src.type == Operand::Type::Reg) { if (dst.type == Operand::Type::Reg && src.type == Operand::Type::Reg) {
if (src.reg == dst.reg) if (src.reg == dst.reg)
@ -122,9 +127,9 @@ struct Assembler {
} }
if (dst.type == Operand::Type::Reg && src.type == Operand::Type::Imm64) { if (dst.type == Operand::Type::Reg && src.type == Operand::Type::Imm64) {
if (src.offset_or_immediate == 0) { if (patchable == Patchable::No && src.offset_or_immediate == 0) {
// xor dst, dst // xor dst, dst
emit8(0x48 | ((to_underlying(dst.reg) >= 8) ? 1 << 0 : 0)); emit8(0x48 | ((to_underlying(dst.reg) >= 8) ? (1 << 0 | 1 << 2) : 0));
emit8(0x31); emit8(0x31);
emit8(0xc0 | (encode_reg(dst.reg) << 3) | encode_reg(dst.reg)); emit8(0xc0 | (encode_reg(dst.reg) << 3) | encode_reg(dst.reg));
return; return;

6
Userland/Libraries/LibJS/JIT/Compiler.cpp
View file

@ -357,7 +357,8 @@ void Compiler::push_unwind_context(bool valid, Optional<Bytecode::Label> const&
// push finalizer (patched later) // push finalizer (patched later)
m_assembler.mov( m_assembler.mov(
Assembler::Operand::Register(GPR0), Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm64(0)); Assembler::Operand::Imm64(0),
Assembler::Patchable::Yes);
if (finalizer.has_value()) if (finalizer.has_value())
block_data_for(finalizer.value().block()).absolute_references_to_here.append(m_assembler.m_output.size() - 8); block_data_for(finalizer.value().block()).absolute_references_to_here.append(m_assembler.m_output.size() - 8);
m_assembler.push(Assembler::Operand::Register(GPR0)); m_assembler.push(Assembler::Operand::Register(GPR0));
@ -365,7 +366,8 @@ void Compiler::push_unwind_context(bool valid, Optional<Bytecode::Label> const&
// push handler (patched later) // push handler (patched later)
m_assembler.mov( m_assembler.mov(
Assembler::Operand::Register(GPR0), Assembler::Operand::Register(GPR0),
Assembler::Operand::Imm64(0)); Assembler::Operand::Imm64(0),
Assembler::Patchable::Yes);
if (handler.has_value()) if (handler.has_value())
block_data_for(handler.value().block()).absolute_references_to_here.append(m_assembler.m_output.size() - 8); block_data_for(handler.value().block()).absolute_references_to_here.append(m_assembler.m_output.size() - 8);
m_assembler.push(Assembler::Operand::Register(GPR0)); m_assembler.push(Assembler::Operand::Register(GPR0));