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[llvm-exegesis][AArch64] Disable pauth and ldgm as unsupported instructions fixed (#136868)

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[llvm-exegesis][AArch64] Recommit: Disable pauth and ldgm as unsupported instructions.

Skipping AUT and LDGM opcode variants which currently throws "illegal
instruction".

Last pull request
[#132346](https://github.com/llvm/llvm-project/pull/132346) got reviewed
and merged but builder bot got failed. This was due to undefined
`PR_PAC_SET_ENABLED_KEYS` utilized were not defined in x86 arch,
resulting in build failure.

This is followup to merge the changes with following changes to fixup
the build failure.

Changes: 
- Fixed up the problem with arch specific check for `prctl` library
import
- Defining `PR_PAC_SET_ENABLED_KEYS` if undefined.
This commit is contained in:
Lakshay Kumar
2025-04-28 15:30:14 +05:30
committed by GitHub
parent 0b6d71fe10
commit 475531b884
2 changed files with 91 additions and 0 deletions
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10
llvm/test/tools/llvm-exegesis/AArch64/skip_unsupported_instructions.s Normal file
View File

@@ -0,0 +1,10 @@
llvm/test/tools/llvm-exegesis/AArch64/skip_unsupported_instructions.s
# REQUIRES: aarch64-registered-target
# Check for skipping of illegal instruction errors (AUT and LDGM)
# RUN: llvm-exegesis -mcpu=neoverse-v2 -mode=latency --opcode-name=AUTIA --benchmark-phase=assemble-measured-code 2>&1 | FileCheck %s --check-prefix=CHECK-AUTIA
# CHECK-AUTIA-NOT: snippet crashed while running: Illegal instruction
# RUN: llvm-exegesis -mcpu=neoverse-v2 -mode=latency --opcode-name=LDGM --benchmark-phase=assemble-measured-code 2>&1 | FileCheck %s --check-prefix=CHECK-LDGM
# CHECK-LDGM: LDGM: Unsupported opcode: load tag multiple

81
llvm/tools/llvm-exegesis/lib/AArch64/Target.cpp
View File

@@ -9,12 +9,64 @@
#include "AArch64.h"
#include "AArch64RegisterInfo.h"
#if defined(__aarch64__) && defined(__linux__)
#include <linux/prctl.h> // For PR_PAC_* constants
#include <sys/prctl.h>
#ifndef PR_PAC_SET_ENABLED_KEYS
#define PR_PAC_SET_ENABLED_KEYS 60
#endif
#ifndef PR_PAC_GET_ENABLED_KEYS
#define PR_PAC_GET_ENABLED_KEYS 61
#endif
#endif
#define GET_AVAILABLE_OPCODE_CHECKER
#include "AArch64GenInstrInfo.inc"
namespace llvm {
namespace exegesis {
bool isPointerAuth(unsigned Opcode) {
switch (Opcode) {
default:
return false;
// FIXME: Pointer Authentication instructions.
// We would like to measure these instructions, but they can behave
// differently on different platforms, and maybe the snippets need to look
// different for these instructions,
// Platform-specific handling: On Linux, we disable authentication, may
// interfere with measurements. On non-Linux platforms, disable opcodes for
// now.
case AArch64::AUTDA:
case AArch64::AUTDB:
case AArch64::AUTDZA:
case AArch64::AUTDZB:
case AArch64::AUTIA:
case AArch64::AUTIA1716:
case AArch64::AUTIASP:
case AArch64::AUTIAZ:
case AArch64::AUTIB:
case AArch64::AUTIB1716:
case AArch64::AUTIBSP:
case AArch64::AUTIBZ:
case AArch64::AUTIZA:
case AArch64::AUTIZB:
return true;
}
}
bool isLoadTagMultiple(unsigned Opcode) {
switch (Opcode) {
default:
return false;
// Load tag multiple instruction
case AArch64::LDGM:
return true;
}
}
static unsigned getLoadImmediateOpcode(unsigned RegBitWidth) {
switch (RegBitWidth) {
case 32:
@@ -134,6 +186,35 @@ private:
// Function return is a pseudo-instruction that needs to be expanded
PM.add(createAArch64ExpandPseudoPass());
}
const char *getIgnoredOpcodeReasonOrNull(const LLVMState &State,
unsigned Opcode) const override {
if (const char *Reason =
ExegesisTarget::getIgnoredOpcodeReasonOrNull(State, Opcode))
return Reason;
if (isPointerAuth(Opcode)) {
#if defined(__aarch64__) && defined(__linux__)
// Disable all PAC keys. Note that while we expect the measurements to
// be the same with PAC keys disabled, they could potentially be lower
// since authentication checks are bypassed.
if (prctl(PR_PAC_SET_ENABLED_KEYS,
PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY |
PR_PAC_APDBKEY, // all keys
0, // disable all
0, 0) < 0) {
return "Failed to disable PAC keys";
}
#else
return "Unsupported opcode: isPointerAuth";
#endif
}
if (isLoadTagMultiple(Opcode))
return "Unsupported opcode: load tag multiple";
return nullptr;
}
};
} // namespace