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Fix linker failure when building Opcache statically

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We use linker relocations to fetch the TLS index and offset of _tsrm_ls_cache.
When building Opcache statically, linkers may attempt to optimize that into a
more efficient code sequence (relaxing from "General Dynamic" to "Local Exec"
model [1]). Unfortunately, linkers will fail, rather than ignore our
relocations, when they don't recognize the exact code sequence they are
expecting.

This results in errors as reported by GH-15074:

    TLS transition from R_X86_64_TLSGD to R_X86_64_GOTTPOFF against
    `_tsrm_ls_cache' at 0x12fc3 in section `.text' failed"

Here I take a different approach:

 * Emit the exact full code sequence expected by linkers
 * Extract the TLS index/offset by inspecting the linked ASM code, rather than
   executing it (execution would give us the thread-local address).
 * We detect when the code was relaxed, in which case we can extract the TCB
   offset instead.
 * This is done in a conservative way so that if the linker did something we
   didn't expect, we fallback to a safer (but slower) mechanism.

One additional benefit of that is we are now able to use the Local Exec model in
more cases, in JIT'ed code. This makes non-glibc builds faster in these cases.

Closes GH-18939.

Related RFC: https://wiki.php.net/rfc/make_opcache_required.

[1] https://www.akkadia.org/drepper/tls.pdf
This commit is contained in:
Arnaud Le Blanc 2025-06-24 11:29:23 +02:00
parent 04feb452ba
commit 73b1ebfa20
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17 changed files with 2402 additions and 171 deletions
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81
run-extra-tests.php
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@ -62,11 +62,90 @@ function main(int $argc, array $argv): void
echo "DEBUG: " . ($environment->debug ? 'Yes' : 'No') . "\n";
echo "=====================================================================\n";
echo "No tests in this branch yet.\n";
try {
output_group_start($environment, 'Running Opcache TLS tests');
if (!run_opcache_tls_tests($environment)) {
echo "Failed\n";
exit(1);
}
} finally {
output_group_end($environment);
}
echo "All OK\n";
}
function run_opcache_tls_tests(Environment $environment): bool
{
if (!$environment->zts) {
echo "Skipping: NTS\n";
return true;
}
if (!$environment->debug) {
echo "Skipping: NDEBUG\n";
return true;
}
$tlsc = '';
$machine = '';
$static_support = 'yes';
switch ($environment->cpuArch) {
case 'x86':
$machine = '-m32';
break;
case 'x86_64':
case 'aarch64':
break;
default:
echo "Skipping: {$environment->cpuArch}\n";
return true;
}
switch ($environment->os) {
case 'Linux':
case 'FreeBSD':
$tlsc = __DIR__ . "/ext/opcache/jit/tls/zend_jit_tls_{$environment->cpuArch}.c";
break;
case 'Darwin':
if ($environment->cpuArch === 'aarch64') {
echo "Skipping: JIT+TLS not supported on MacOS Apple Silicon\n";
return true;
}
$tlsc = __DIR__ . "/ext/opcache/jit/tls/zend_jit_tls_darwin.c";
$static_support = 'no';
break;
default:
echo "Skipping: {$environment->os}\n";
return true;
}
echo "TLSC=$tlsc MACHINE=$machine STATIC_SUPPORT=$static_support ext/opcache/jit/tls/testing/test.sh\n";
$proc = proc_open(
__DIR__ . '/ext/opcache/jit/tls/testing/test.sh',
[
0 => ['pipe', 'r'],
],
$pipes,
env_vars: array_merge(getenv(), [
'TLSC' => $tlsc,
'MACHINE' => $machine,
'STATIC_SUPPORT' => $static_support,
]),
);
if (!$proc) {
echo "proc_open() failed\n";
return false;
}
fclose($pipes[0]);
return proc_close($proc) === 0;
}
function output_group_start(Environment $environment, string $name): void
{
if ($environment->githubAction) {