Previously, the actual behavior of magic lookup and one described in its
commit description have not matched. Instead of being weak definitions
in a library that is always in the end of load order, the definitions
were normal ones and thus were able to override other weak definitions
in LibC. While this was consistent with how DynamicLoader resolves
ambiguity between normal and weak relocations, this is not the behavior
POSIX mandates -- we should always choose first available definition wrt
load order. To fix this problem, the patch makes sure we don't define
any of magic symbols in LibC.
In addition to this, it makes all provided magic symbols functions
(instead of objects), what renders MagicWeakSymbol class unnecessary.
This works by defining a set of weak symbols in dynamic linker whose
value would be provided by it. This has the same effect as preloading
library that magically knows right addresses of functions shared between
dynamic linker and LibC.
We were previously passing the same information by rewriting values
based on hardcoded library name, so the new approach seems a little
nicer to me.
We already set these variables and call `_init` in the dynamic linker.
As we don't care about static binaries, remove these assignments and the
call to `_init` from `_entry`.
The function referenced by DT_INIT is also not necessarily called
`_init`, so directly calling `_init` is not really correct.
`s_global_initializers_ran` and `__stack_chk_guard` are unused, so
remove them.
It's a bad idea to have a global event loop in a client application as
that will cause an initialization-order fiasco in ASAN. Therefore, LibC
now has a flag "s_global_initializers_ran" which is false until _entry
in crt0 runs, which in turn only gets called after all the global
initializers were actually executed. The EventLoop constructor checks
the flag and crashes the program if it is being called as a global
constructor. A note next to the VERIFY_NOT_REACHED() informs the
developer of these things and how we usually instantiate event loops.
The upshot of this is that global event loops will cause a crash before
any undefined behavior is hit.
Previously, getauxval() got the address of the auxiliary vector by
traversing to the end of the `environ` pointer.
The assumption that the auxiliary vector comes after the environment
array is true at program startup, however the environment array may
be re-allocated and change its address during runtime which would cause
getauxval() to work with an incorrect auxiliary vector address.
To fix this, we now get the address of the auxiliary vector once in
__libc_init and store it in a libc-internal pointer which is then used
by getauxval().
Fixes#10087.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
