mirror of
https://github.com/php/php-src.git
synced 2026-03-24 00:02:20 +01:00
73b1ebfa20
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
41 lines
1.5 KiB
C
41 lines
1.5 KiB
C
/*
|
|
* +----------------------------------------------------------------------+
|
|
* | Zend JIT |
|
|
* +----------------------------------------------------------------------+
|
|
* | Copyright (c) The PHP Group |
|
|
* +----------------------------------------------------------------------+
|
|
* | This source file is subject to version 3.01 of the PHP license, |
|
|
* | that is bundled with this package in the file LICENSE, and is |
|
|
* | available through the world-wide-web at the following url: |
|
|
* | https://www.php.net/license/3_01.txt |
|
|
* | If you did not receive a copy of the PHP license and are unable to |
|
|
* | obtain it through the world-wide-web, please send a note to |
|
|
* | license@php.net so we can mail you a copy immediately. |
|
|
* +----------------------------------------------------------------------+
|
|
* | Authors: Arnaud Le Blanc <arnaud.lb@gmail.com> |
|
|
* +----------------------------------------------------------------------+
|
|
*/
|
|
|
|
#ifndef ZEND_JIT_TLS_H
|
|
#define ZEND_JIT_TLS_H
|
|
|
|
#include "Zend/zend_types.h"
|
|
|
|
#include <stdint.h>
|
|
#include <stddef.h>
|
|
|
|
zend_result zend_jit_resolve_tsrm_ls_cache_offsets(
|
|
size_t *tcb_offset,
|
|
size_t *module_index,
|
|
size_t *module_offset
|
|
);
|
|
|
|
/* Used for testing */
|
|
void *zend_jit_tsrm_ls_cache_address(
|
|
size_t tcb_offset,
|
|
size_t module_index,
|
|
size_t module_offset
|
|
);
|
|
|
|
#endif /* ZEND_JIT_TLS_H */
|