// 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");
}