diff options
Diffstat (limited to 'tools/testing/selftests/powerpc/tm/tm-trap.c')
| -rw-r--r-- | tools/testing/selftests/powerpc/tm/tm-trap.c | 334 |
1 files changed, 334 insertions, 0 deletions
diff --git a/tools/testing/selftests/powerpc/tm/tm-trap.c b/tools/testing/selftests/powerpc/tm/tm-trap.c new file mode 100644 index 000000000..97cb74768 --- /dev/null +++ b/tools/testing/selftests/powerpc/tm/tm-trap.c @@ -0,0 +1,334 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright 2017, Gustavo Romero, IBM Corp. + * + * Check if thread endianness is flipped inadvertently to BE on trap + * caught in TM whilst MSR.FP and MSR.VEC are zero (i.e. just after + * load_fp and load_vec overflowed). + * + * The issue can be checked on LE machines simply by zeroing load_fp + * and load_vec and then causing a trap in TM. Since the endianness + * changes to BE on return from the signal handler, 'nop' is + * thread as an illegal instruction in following sequence: + * tbegin. + * beq 1f + * trap + * tend. + * 1: nop + * + * However, although the issue is also present on BE machines, it's a + * bit trickier to check it on BE machines because MSR.LE bit is set + * to zero which determines a BE endianness that is the native + * endianness on BE machines, so nothing notably critical happens, + * i.e. no illegal instruction is observed immediately after returning + * from the signal handler (as it happens on LE machines). Thus to test + * it on BE machines LE endianness is forced after a first trap and then + * the endianness is verified on subsequent traps to determine if the + * endianness "flipped back" to the native endianness (BE). + */ + +#define _GNU_SOURCE +#include <error.h> +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <htmintrin.h> +#include <inttypes.h> +#include <pthread.h> +#include <sched.h> +#include <signal.h> +#include <stdbool.h> + +#include "tm.h" +#include "utils.h" + +#define pr_error(error_code, format, ...) \ + error_at_line(1, error_code, __FILE__, __LINE__, format, ##__VA_ARGS__) + +#define MSR_LE 1UL +#define LE 1UL + +pthread_t t0_ping; +pthread_t t1_pong; + +int exit_from_pong; + +int trap_event; +int le; + +bool success; + +void trap_signal_handler(int signo, siginfo_t *si, void *uc) +{ + ucontext_t *ucp = uc; + uint64_t thread_endianness; + + /* Get thread endianness: extract bit LE from MSR */ + thread_endianness = MSR_LE & ucp->uc_mcontext.gp_regs[PT_MSR]; + + /* + * Little-Endian Machine + */ + + if (le) { + /* First trap event */ + if (trap_event == 0) { + /* Do nothing. Since it is returning from this trap + * event that endianness is flipped by the bug, so just + * let the process return from the signal handler and + * check on the second trap event if endianness is + * flipped or not. + */ + } + /* Second trap event */ + else if (trap_event == 1) { + /* + * Since trap was caught in TM on first trap event, if + * endianness was still LE (not flipped inadvertently) + * after returning from the signal handler instruction + * (1) is executed (basically a 'nop'), as it's located + * at address of tbegin. +4 (rollback addr). As (1) on + * LE endianness does in effect nothing, instruction (2) + * is then executed again as 'trap', generating a second + * trap event (note that in that case 'trap' is caught + * not in transacional mode). On te other hand, if after + * the return from the signal handler the endianness in- + * advertently flipped, instruction (1) is tread as a + * branch instruction, i.e. b .+8, hence instruction (3) + * and (4) are executed (tbegin.; trap;) and we get sim- + * ilaly on the trap signal handler, but now in TM mode. + * Either way, it's now possible to check the MSR LE bit + * once in the trap handler to verify if endianness was + * flipped or not after the return from the second trap + * event. If endianness is flipped, the bug is present. + * Finally, getting a trap in TM mode or not is just + * worth noting because it affects the math to determine + * the offset added to the NIP on return: the NIP for a + * trap caught in TM is the rollback address, i.e. the + * next instruction after 'tbegin.', whilst the NIP for + * a trap caught in non-transactional mode is the very + * same address of the 'trap' instruction that generated + * the trap event. + */ + + if (thread_endianness == LE) { + /* Go to 'success', i.e. instruction (6) */ + ucp->uc_mcontext.gp_regs[PT_NIP] += 16; + } else { + /* + * Thread endianness is BE, so it flipped + * inadvertently. Thus we flip back to LE and + * set NIP to go to 'failure', instruction (5). + */ + ucp->uc_mcontext.gp_regs[PT_MSR] |= 1UL; + ucp->uc_mcontext.gp_regs[PT_NIP] += 4; + } + } + } + + /* + * Big-Endian Machine + */ + + else { + /* First trap event */ + if (trap_event == 0) { + /* + * Force thread endianness to be LE. Instructions (1), + * (3), and (4) will be executed, generating a second + * trap in TM mode. + */ + ucp->uc_mcontext.gp_regs[PT_MSR] |= 1UL; + } + /* Second trap event */ + else if (trap_event == 1) { + /* + * Do nothing. If bug is present on return from this + * second trap event endianness will flip back "automat- + * ically" to BE, otherwise thread endianness will + * continue to be LE, just as it was set above. + */ + } + /* A third trap event */ + else { + /* + * Once here it means that after returning from the sec- + * ond trap event instruction (4) (trap) was executed + * as LE, generating a third trap event. In that case + * endianness is still LE as set on return from the + * first trap event, hence no bug. Otherwise, bug + * flipped back to BE on return from the second trap + * event and instruction (4) was executed as 'tdi' (so + * basically a 'nop') and branch to 'failure' in + * instruction (5) was taken to indicate failure and we + * never get here. + */ + + /* + * Flip back to BE and go to instruction (6), i.e. go to + * 'success'. + */ + ucp->uc_mcontext.gp_regs[PT_MSR] &= ~1UL; + ucp->uc_mcontext.gp_regs[PT_NIP] += 8; + } + } + + trap_event++; +} + +void usr1_signal_handler(int signo, siginfo_t *si, void *not_used) +{ + /* Got a USR1 signal from ping(), so just tell pong() to exit */ + exit_from_pong = 1; +} + +void *ping(void *not_used) +{ + uint64_t i; + + trap_event = 0; + + /* + * Wait an amount of context switches so load_fp and load_vec overflows + * and MSR_[FP|VEC|V] is 0. + */ + for (i = 0; i < 1024*1024*512; i++) + ; + + asm goto( + /* + * [NA] means "Native Endianness", i.e. it tells how a + * instruction is executed on machine's native endianness (in + * other words, native endianness matches kernel endianness). + * [OP] means "Opposite Endianness", i.e. on a BE machine, it + * tells how a instruction is executed as a LE instruction; con- + * versely, on a LE machine, it tells how a instruction is + * executed as a BE instruction. When [NA] is omitted, it means + * that the native interpretation of a given instruction is not + * relevant for the test. Likewise when [OP] is omitted. + */ + + " tbegin. ;" /* (0) tbegin. [NA] */ + " tdi 0, 0, 0x48;" /* (1) nop [NA]; b (3) [OP] */ + " trap ;" /* (2) trap [NA] */ + ".long 0x1D05007C;" /* (3) tbegin. [OP] */ + ".long 0x0800E07F;" /* (4) trap [OP]; nop [NA] */ + " b %l[failure] ;" /* (5) b [NA]; MSR.LE flipped (bug) */ + " b %l[success] ;" /* (6) b [NA]; MSR.LE did not flip (ok)*/ + + : : : : failure, success); + +failure: + success = false; + goto exit_from_ping; + +success: + success = true; + +exit_from_ping: + /* Tell pong() to exit before leaving */ + pthread_kill(t1_pong, SIGUSR1); + return NULL; +} + +void *pong(void *not_used) +{ + while (!exit_from_pong) + /* + * Induce context switches on ping() thread + * until ping() finishes its job and signs + * to exit from this loop. + */ + sched_yield(); + + return NULL; +} + +int tm_trap_test(void) +{ + uint16_t k = 1; + int cpu, rc; + + pthread_attr_t attr; + cpu_set_t cpuset; + + struct sigaction trap_sa; + + SKIP_IF(!have_htm()); + SKIP_IF(htm_is_synthetic()); + + trap_sa.sa_flags = SA_SIGINFO; + trap_sa.sa_sigaction = trap_signal_handler; + sigaction(SIGTRAP, &trap_sa, NULL); + + struct sigaction usr1_sa; + + usr1_sa.sa_flags = SA_SIGINFO; + usr1_sa.sa_sigaction = usr1_signal_handler; + sigaction(SIGUSR1, &usr1_sa, NULL); + + cpu = pick_online_cpu(); + FAIL_IF(cpu < 0); + + // Set only one CPU in the mask. Both threads will be bound to that CPU. + CPU_ZERO(&cpuset); + CPU_SET(cpu, &cpuset); + + /* Init pthread attribute */ + rc = pthread_attr_init(&attr); + if (rc) + pr_error(rc, "pthread_attr_init()"); + + /* + * Bind thread ping() and pong() both to CPU 0 so they ping-pong and + * speed up context switches on ping() thread, speeding up the load_fp + * and load_vec overflow. + */ + rc = pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &cpuset); + if (rc) + pr_error(rc, "pthread_attr_setaffinity()"); + + /* Figure out the machine endianness */ + le = (int) *(uint8_t *)&k; + + printf("%s machine detected. Checking if endianness flips %s", + le ? "Little-Endian" : "Big-Endian", + "inadvertently on trap in TM... "); + + rc = fflush(0); + if (rc) + pr_error(rc, "fflush()"); + + /* Launch ping() */ + rc = pthread_create(&t0_ping, &attr, ping, NULL); + if (rc) + pr_error(rc, "pthread_create()"); + + exit_from_pong = 0; + + /* Launch pong() */ + rc = pthread_create(&t1_pong, &attr, pong, NULL); + if (rc) + pr_error(rc, "pthread_create()"); + + rc = pthread_join(t0_ping, NULL); + if (rc) + pr_error(rc, "pthread_join()"); + + rc = pthread_join(t1_pong, NULL); + if (rc) + pr_error(rc, "pthread_join()"); + + if (success) { + printf("no.\n"); /* no, endianness did not flip inadvertently */ + return EXIT_SUCCESS; + } + + printf("yes!\n"); /* yes, endianness did flip inadvertently */ + return EXIT_FAILURE; +} + +int main(int argc, char **argv) +{ + return test_harness(tm_trap_test, "tm_trap_test"); +} |