From 4d1e23e3b3cd7c72a8b24dc5acb7e13c58a8de37 Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Fri, 3 Jan 2020 00:35:47 -0800 Subject: [AArch64] Add function attribute "patchable-function-entry" to add NOPs at function entry The Linux kernel uses -fpatchable-function-entry to implement DYNAMIC_FTRACE_WITH_REGS for arm64 and parisc. GCC 8 implemented -fpatchable-function-entry, which can be seen as a generalized form of -mnop-mcount. The N,M form (function entry points before the Mth NOP) is currently only used by parisc. This patch adds N,0 support to AArch64 codegen. N is represented as the function attribute "patchable-function-entry". We will use a different function attribute for M, if we decide to implement it. The patch reuses the existing patchable-function pass, and TargetOpcode::PATCHABLE_FUNCTION_ENTER which is currently used by XRay. When the integrated assembler is used, __patchable_function_entries will be created for each text section with the SHF_LINK_ORDER flag to prevent --gc-sections (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93197) and COMDAT (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93195) issues. Retrospectively, __patchable_function_entries should use a PC-relative relocation type to avoid the SHF_WRITE flag and dynamic relocations. "patchable-function-entry"'s interaction with Branch Target Identification is still unclear (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92424 for GCC discussions). Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D72215 --- llvm/lib/CodeGen/PatchableFunction.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'llvm/lib/CodeGen/PatchableFunction.cpp') diff --git a/llvm/lib/CodeGen/PatchableFunction.cpp b/llvm/lib/CodeGen/PatchableFunction.cpp index f499241d43c..1d6069c5055 100644 --- a/llvm/lib/CodeGen/PatchableFunction.cpp +++ b/llvm/lib/CodeGen/PatchableFunction.cpp @@ -55,6 +55,15 @@ static bool doesNotGeneratecode(const MachineInstr &MI) { } bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) { + if (MF.getFunction().hasFnAttribute("patchable-function-entry")) { + MachineBasicBlock &FirstMBB = *MF.begin(); + MachineInstr &FirstMI = *FirstMBB.begin(); + const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); + BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(), + TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER)); + return true; + } + if (!MF.getFunction().hasFnAttribute("patchable-function")) return false; -- cgit v1.2.3