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
We are adding extra (non-phpt) test suites in [1] and [2]. In order to
avoid touching CI files too often (which are maintained in 8.1 and merged in
upper branches), we add a single entry point to call the extra tests. The entry
point can be updated in branches without synchronizing all the way from 8.1.
CI files still need to be touched to install dependencies of these tests,
but this should be manageable as these do not change often and are the same
in every branch.
Closes GH-19242.
[1] https://github.com/php/php-src/pull/16987
[2] https://github.com/php/php-src/pull/18939
