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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
82 lines
2.3 KiB
C
82 lines
2.3 KiB
C
/*
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* +----------------------------------------------------------------------+
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* | Zend JIT |
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* +----------------------------------------------------------------------+
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* | Copyright (c) The PHP Group |
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* +----------------------------------------------------------------------+
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* | This source file is subject to version 3.01 of the PHP license, |
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* | that is bundled with this package in the file LICENSE, and is |
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* | available through the world-wide-web at the following url: |
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* | https://www.php.net/license/3_01.txt |
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* | If you did not receive a copy of the PHP license and are unable to |
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* | obtain it through the world-wide-web, please send a note to |
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* | license@php.net so we can mail you a copy immediately. |
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* +----------------------------------------------------------------------+
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* | Authors: Dmitry Stogov <dmitry@php.net> |
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* +----------------------------------------------------------------------+
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*/
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#include "Zend/zend_portability.h"
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#include "Zend/zend_types.h"
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#include "TSRM/TSRM.h"
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#include "zend_accelerator_debug.h"
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#include <stdint.h>
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#include <unistd.h>
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TSRMLS_CACHE_EXTERN();
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zend_result zend_jit_resolve_tsrm_ls_cache_offsets(
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size_t *tcb_offset,
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size_t *module_index,
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size_t *module_offset
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) {
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*tcb_offset = tsrm_get_ls_cache_tcb_offset();
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if (*tcb_offset != 0) {
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return SUCCESS;
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}
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#if defined(__x86_64__)
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size_t *ti;
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__asm__ __volatile__(
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"leaq __tsrm_ls_cache(%%rip),%0"
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: "=r" (ti));
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*module_offset = ti[2];
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*module_index = ti[1] * 8;
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return SUCCESS;
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#endif
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return FAILURE;
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}
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/* Used for testing */
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void *zend_jit_tsrm_ls_cache_address(
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size_t tcb_offset,
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size_t module_index,
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size_t module_offset
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) {
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#if defined(__x86_64__)
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if (tcb_offset) {
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char *addr;
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__asm__ __volatile__(
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"movq %%gs:(%1), %0\n"
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: "=r" (addr)
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: "r" (tcb_offset)
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);
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return addr;
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}
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if (module_index != (size_t)-1 && module_offset != (size_t)-1) {
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char *base;
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__asm__ __volatile__(
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"movq %%gs:(%1), %0\n"
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: "=r" (base)
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: "r" (module_index)
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);
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return base + module_offset;
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}
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#endif
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return NULL;
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}
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