[BOLT] Don't terminate on trap instruction for Linux kernel #87021
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Under normal circumstances, we terminate basic blocks on a trap instruction. However, Linux kernel may resume execution after hitting a trap (ud2 on x86). Thus, we introduce "--terminal-trap" option that will specify if the trap instruction should terminate the control flow. The option is on by default except for the Linux kernel mode when it's off.
maksfb
requested review from
aaupov,
rafaelauler,
ayermolo and
dcci
as code owners
aaupov
approved these changes
Mar 28, 2024
Comment on lines
-217
to
-218
| return Info->get(Opcode).isTerminator() || X86::isUD1(Opcode) || | ||
| X86::isUD2(Opcode); |
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Assuming you tested that it's safe to drop ud1/ud2 from terminators.
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I'm dropping them only for the Linux kernel. For the rest, by default they will still terminate, but the condition check is modified with isTrap() check instead of the opcode lookup.
dcci
approved these changes
Mar 29, 2024
maksfb
commented
Mar 29, 2024
| @@ -121,6 +130,11 @@ bool MCPlusBuilder::equals(const MCTargetExpr &A, const MCTargetExpr &B, | |||
| llvm_unreachable("target-specific expressions are unsupported"); | |||
| } | |||
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| bool MCPlusBuilder::isTerminator(const MCInst &Inst) const { | |||
| return Analysis->isTerminator(Inst) || | |||
| (opts::TerminalTrap && Info->get(Inst.getOpcode()).isTrap()); | |||
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Under normal circumstances, we terminate basic blocks on a trap instruction. However, Linux kernel may resume execution after hitting a trap (ud2 on x86). Thus, we introduce "--terminal-trap" option that will specify if the trap instruction should terminate the control flow. The option is on by default except for the Linux kernel mode when it's off.