853a498f2c
The BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF is not working for
signal/sigaction/fork. The reason is that the code stops bound checking
for the whole application. This result in wrong handling of
__bound_local_new/__bound_local_delete and malloc/calloc/realloc/free.
Consider the following code:
void tst(int n) {
int i, arr[n];
for (i = 0; i < n; i++) arr[i] = 0;
}
void *some_thread(void *dummy) {
while (running) { tst(10); tst(20); }
}
void signal_handler(int sig) { ... }
When the signal handler is called the some_thread code can be interrupted when
is just registered the arr[10] data. When the signal handler is leaved the
arr[10] is still registered and did not see the call to deregister arr[10] and
then register arr[20]. The code resumes when tst(20) is running. This results
in a bound checking error when i >= 10.
To solve the above problem I changed the bound checking code to use
tls (thread local storage) for the no_checking variable.
This also makes it now possible to redirect signal/sigaction/fork code
through the bound checking library and disable checking when a signal is
running and to correct the bounds_sem for the fork child process.
The BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF is not needed any more for
signal/sigaction/fork. In fact I could remove them from all my applications.
The use of the tls function code slows down the code by about 10%.
So if the slowdown due to bound checking was 5. It is now 5.5 times slower.
For x86_64/i386 I also allowed to use __thread variable in bcheck.c when
compiled with gcc with:
make x86_64-libtcc1-usegcc=yes
make i386-libtcc1-usegcc=yes
This makes code run faster due to use of gcc and __thread variable.
With the __thread variable there is no 10% slowdown.
For other targets this does not work because stabs is not supported.
Changes:
lib/bcheck.c:
- Add TRY_SEM
- Add HAVE_SIGNAL/HAVE_SIGACTION/HAVE_FORK/HAVE_TLS_FUNC/HAVE_TLS_VAR
- HAVE_SIGNAL: redirect signal() call if set.
- HAVE_SIGACTION: redirect sigaction() call if set.
- HAVE_FORK: redirect fork() call if set.
- HAVE_TLS_FUNC: If target has tls function calls.
- HAVE_TLS_VAR: If target has __thread tls support.
- Replace all no_checking refecrences to NO_CHECKING_SET/NO_CHECKING_GET macros
tcc-doc.texi:
- Remove examples for signal/sigaction/fork code.
- Add some explanation for signal/sigaction/fork code.
- Add documentaion for __bounds_checking().
tccelf.c:
- Add support for SHF_TLS
tests/tests2/114_bound_signal.c:
- Remove BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF
- Add code to trigger failure when tls is not working.
x86_64-link.c:
- Add support for R_X86_64_TLSGD/R_X86_64_TLSLD/R_X86_64_DTPOFF32/R_X86_64_TPOFF32
i386-link.c:
- Add support for R_386_TLS_GD/R_386_TLS_LDM/R_386_TLS_LDO_32/R_386_TLS_LE
98 lines
1.8 KiB
C
98 lines
1.8 KiB
C
#include <stdio.h>
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#include <pthread.h>
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#include <semaphore.h>
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#include <signal.h>
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#include <string.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <errno.h>
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#include <setjmp.h>
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static volatile int run = 1;
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static sem_t sem;
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static void
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add (int n)
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{
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int i;
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int arr[n];
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for (i = 0; i < n; i++) {
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arr[i]++;
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}
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memset (&arr[0], 0, n * sizeof(int));
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}
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static void *
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high_load (void *unused)
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{
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while (run) {
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add(10);
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add(20);
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}
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return NULL;
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}
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static void *
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do_signal (void *unused)
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{
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while (run) {
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kill (getpid(), SIGUSR1);
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while (sem_wait(&sem) < 0 && errno == EINTR);
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}
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return NULL;
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}
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static void signal_handler(int sig)
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{
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add(10);
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add(20);
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sem_post (&sem);
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}
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int
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main (void)
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{
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int i;
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pthread_t id1, id2;
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struct sigaction act;
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sigjmp_buf sj;
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sigset_t m;
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time_t end;
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memset (&act, 0, sizeof (act));
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act.sa_handler = signal_handler;
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act.sa_flags = 0;
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sigemptyset (&act.sa_mask);
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sigaction (SIGUSR1, &act, NULL);
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sem_init (&sem, 1, 0);
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pthread_create(&id1, NULL, high_load, NULL);
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pthread_create(&id2, NULL, do_signal, NULL);
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printf ("start\n");
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/* sleep does not work !!! */
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end = time(NULL) + 2;
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while (time(NULL) < end) ;
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run = 0;
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printf ("end\n");
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pthread_join(id1, NULL);
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pthread_join(id2, NULL);
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sem_destroy (&sem);
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sigemptyset (&m);
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sigprocmask (SIG_SETMASK, &m, NULL);
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if (sigsetjmp (sj, 0) == 0)
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{
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sigaddset (&m, SIGUSR1);
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sigprocmask (SIG_SETMASK, &m, NULL);
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siglongjmp (sj, 1);
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printf ("failed");
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return 1;
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}
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sigprocmask (SIG_SETMASK, NULL, &m);
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if (!sigismember (&m, SIGUSR1))
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printf ("failed");
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return 0;
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}
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