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Fix GH-17990: Tracing JIT uses the SSA of a dead process #25399

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Fix GH-17990: Tracing JIT uses the SSA of a dead process #25399

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25 changes: 23 additions & 2 deletions ext/opcache/jit/zend_jit_trace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1295,6 +1295,21 @@ typedef struct _zend_tssa {

static const zend_op _nop_opcode = {0};

/* The func_info of an op_array lives in shared memory, but its SSA is allocated
* in the arena of the process that compiles a trace, and zend_jit_trace() resets
* it when the compilation ends. A process that dies in the middle of a
* compilation leaves its SSA behind, so a non-zero ssa->cfg.blocks_count does
* not prove that the SSA was built by the current compilation. */
static bool zend_jit_trace_has_ssa(const zend_jit_op_array_trace_extension *jit_extension, const zend_op_array **op_arrays, int num_op_arrays)
{
for (int i = 0; i < num_op_arrays; i++) {
if ((const void*)ZEND_FUNC_INFO(op_arrays[i]) == (const void*)jit_extension) {
return true;
}
}
return false;
}

static zend_ssa *zend_jit_trace_build_tssa(zend_jit_trace_rec *trace_buffer, uint32_t parent_trace, uint32_t exit_num, zend_script *script, const zend_op_array **op_arrays, int *num_op_arrays_ptr)
{
zend_ssa *tssa;
Expand Down Expand Up @@ -1398,7 +1413,7 @@ static zend_ssa *zend_jit_trace_build_tssa(zend_jit_trace_rec *trace_buffer, uin
jit_extension =
(zend_jit_op_array_trace_extension*)ZEND_FUNC_INFO(op_array);
ssa = &jit_extension->func_info.ssa;
if (ssa->cfg.blocks_count) {
if (zend_jit_trace_has_ssa(jit_extension, op_arrays, num_op_arrays)) {
/* pass */
} else if (num_op_arrays == ZEND_JIT_TRACE_MAX_FUNCS) {
/* Too many functions in single trace */
Expand All @@ -1416,7 +1431,7 @@ static zend_ssa *zend_jit_trace_build_tssa(zend_jit_trace_rec *trace_buffer, uin
jit_extension =
(zend_jit_op_array_trace_extension*)ZEND_FUNC_INFO(op_array);
ssa = &jit_extension->func_info.ssa;
if (ssa->cfg.blocks_count) {
if (zend_jit_trace_has_ssa(jit_extension, op_arrays, num_op_arrays)) {
/* pass */
} else if (num_op_arrays == ZEND_JIT_TRACE_MAX_FUNCS) {
/* Too many functions in single trace */
Expand Down Expand Up @@ -7450,6 +7465,8 @@ static zend_jit_trace_stop zend_jit_compile_root_trace(zend_jit_trace_rec *trace
zend_jit_trace_exit_info exit_info[ZEND_JIT_TRACE_MAX_EXITS];
bool do_bailout = 0;

/* Don't let a signal kill the process while func_info in SHM refers to our arena */

@iliaal iliaal Nov 11, 2026

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This only defers the signals zend_signal handles (SIGTERM, SIGINT, SIGHUP...). SIGKILL, a segfault or the OOM killer still end the process here, and that is the case your test covers. Maybe /* Defer signals while func_info in SHM refers to our arena */?

HANDLE_BLOCK_INTERRUPTIONS();
zend_shared_alloc_lock();

/* Checks under lock */
Expand Down Expand Up @@ -7590,6 +7607,7 @@ exit:;
}

zend_shared_alloc_unlock();
HANDLE_UNBLOCK_INTERRUPTIONS();

if (do_bailout) {
zend_bailout();
Expand Down Expand Up @@ -8288,6 +8306,8 @@ static zend_jit_trace_stop zend_jit_compile_side_trace(zend_jit_trace_rec *trace
zend_jit_trace_exit_info exit_info[ZEND_JIT_TRACE_MAX_EXITS];
bool do_bailout = 0;

/* Don't let a signal kill the process while func_info in SHM refers to our arena */

@iliaal iliaal Nov 11, 2026

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Same as above.

HANDLE_BLOCK_INTERRUPTIONS();
zend_shared_alloc_lock();

/* Checks under lock */
Expand Down Expand Up @@ -8430,6 +8450,7 @@ exit:;
}

zend_shared_alloc_unlock();
HANDLE_UNBLOCK_INTERRUPTIONS();

if (do_bailout) {
zend_bailout();
Expand Down
46 changes: 46 additions & 0 deletions ext/opcache/tests/jit/gh17990.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
--TEST--
GH-17990 (Tracing JIT uses the SSA of a process that died during trace compilation)
--EXTENSIONS--
opcache
pcntl
posix
--INI--
opcache.enable=1
opcache.enable_cli=1
opcache.file_update_protection=0
opcache.jit=tracing
opcache.jit_buffer_size=64M
opcache.jit_hot_func=1
--FILE--
<?php
function foo($x) {
return $x + 42;
}

function test() {
return foo(3);
}

/* Kill a child at different moments, so that one of them dies while it compiles
* the trace of test(). The shutdown function starts that trace outside of any
* other trace. */
for ($delay = 0; $delay <= 2000; $delay += 50) {
$pid = pcntl_fork();
if ($pid === -1) {
die("fork failed\n");
}
if ($pid === 0) {
register_shutdown_function('test');
exit(0);
}
usleep($delay);
posix_kill($pid, SIGKILL);
pcntl_waitpid($pid, $status);
}

register_shutdown_function(function () {
var_dump(test());
});
?>
--EXPECT--
int(45)
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