5cb2c6806e
This patch reimplements the SME ABI `__arm_za_disable` routine within libunwind. This routine must be called before resuming from unwinding on AArch64 platforms with SME support. Before calling the routine, we need to check that SME is available. In this patch, this is implemented for Linux-based platforms by checking HWCAP2. It should be possible to implement this check for other platforms as required. This patch includes a test for this functionality. This test requires SME, so on platforms without it, it will simply pass.
118 lines
3.3 KiB
C++
118 lines
3.3 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// REQUIRES: linux && target={{aarch64-.+}}
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#include <libunwind.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/auxv.h>
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// Basic test of unwinding with SME lazy saves. This tests libunwind disables ZA
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// (and commits a lazy save of ZA) before resuming from unwinding.
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// Note: This test requires SME (and is setup to pass on targets without SME).
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static bool checkHasSME() {
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constexpr int hwcap2_sme = (1 << 23);
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unsigned long hwcap2 = getauxval(AT_HWCAP2);
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return (hwcap2 & hwcap2_sme) != 0;
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}
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struct TPIDR2Block {
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void *za_save_buffer;
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uint64_t num_save_slices;
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};
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__attribute__((noinline)) void private_za() {
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// Note: Lazy save active on entry to function.
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unw_context_t context;
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unw_cursor_t cursor;
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unw_getcontext(&context);
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unw_init_local(&cursor, &context);
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unw_step(&cursor);
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unw_resume(&cursor);
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}
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bool isZAOn() {
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register uint64_t svcr asm("x20");
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asm(".inst 0xd53b4254" : "=r"(svcr));
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return (svcr & 0b10) != 0;
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}
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__attribute__((noinline)) void za_function_with_lazy_save() {
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register uint64_t tmp asm("x8");
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// SMSTART ZA (should zero ZA)
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asm(".inst 0xd503457f");
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// RDSVL x8, #1 (read streaming vector length)
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asm(".inst 0x04bf5828" : "=r"(tmp));
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// Allocate and fill ZA save buffer with 0xAA.
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size_t buffer_size = tmp * tmp;
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uint8_t *za_save_buffer = (uint8_t *)alloca(buffer_size);
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memset(za_save_buffer, 0xAA, buffer_size);
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TPIDR2Block block = {za_save_buffer, tmp};
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tmp = reinterpret_cast<uint64_t>(&block);
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// MRS TPIDR2_EL0, x8 (setup lazy save of ZA)
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asm(".inst 0xd51bd0a8" ::"r"(tmp));
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// ZA should be on before unwinding.
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if (!isZAOn()) {
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fprintf(stderr, __FILE__ ": fail (ZA not on before call)\n");
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abort();
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} else {
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fprintf(stderr, __FILE__ ": pass (ZA on before call)\n");
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}
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private_za();
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// ZA should be off after unwinding.
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if (isZAOn()) {
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fprintf(stderr, __FILE__ ": fail (ZA on after unwinding)\n");
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abort();
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} else {
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fprintf(stderr, __FILE__ ": pass (ZA off after unwinding)\n");
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}
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// MRS x8, TPIDR2_EL0 (read TPIDR2_EL0)
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asm(".inst 0xd53bd0a8" : "=r"(tmp));
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// ZA should have been saved (TPIDR2_EL0 zero).
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if (tmp != 0) {
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fprintf(stderr, __FILE__ ": fail (TPIDR2_EL0 non-null after unwinding)\n");
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abort();
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} else {
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fprintf(stderr, __FILE__ ": pass (TPIDR2_EL0 null after unwinding)\n");
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}
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// ZA (all zero) should have been saved to the buffer.
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for (unsigned i = 0; i < buffer_size; ++i) {
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if (za_save_buffer[i] != 0) {
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fprintf(stderr,
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__FILE__ ": fail (za_save_buffer non-zero after unwinding)\n");
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abort();
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}
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}
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fprintf(stderr, __FILE__ ": pass (za_save_buffer zero'd after unwinding)\n");
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}
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int main(int, char **) {
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if (!checkHasSME()) {
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fprintf(stderr, __FILE__ ": pass (no SME support)\n");
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return 0; // Pass (SME is required for this test to run).
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}
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za_function_with_lazy_save();
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return 0;
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}
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