For a main thread a thread object is created by the CRT0 before _main gets
called so that _main can already run in a generic environment that, e.g.,
catches stack overflows as a page-fault instead of corrupting the BSS.
Additionally dynamic programs have only one CRT0 - the one of the LDSO -
which does the initialization for both LDSO and program.
ref #989
The x86_64 ABI requires the stack pointer to be 16-byte aligned before the
call of a function and decreased by 8 at the function entrypoint (after
the return address has been pushed to the stack).
Currently, when a new Genode thread gets created, the initial stack
pointer is aligned to 16 byte. On Genode/Linux, the thread entry function
is entered by a 'call' instruction, so the stack pointer alignment at the
function entrypoint is correct. On Fiasco.OC and NOVA, however, the thread
entry function gets executed without a return address being pushed to the
stack, so at the function entrypoint the stack pointer is still aligned to
16 byte, which can cause problems with compiler-generated SSE
instructions.
With this patch, the stack pointer given to a new thread gets aligned to
16 bytes and decreased by 8 by default, since most of the currently
supported base platforms execute the thread entry function without pushing
a return address to the stack. For base-linux, the stack pointer gets
realigned to 16 bytes before the thread entry function gets called.
Fixes#1043.
Using the new 'join()' function, the caller can explicitly block for the
completion of the thread's 'entry()' function. The test case for this
feature can be found at 'os/src/test/thread_join'. For hybrid
Linux/Genode programs, the 'Thread_base::join()' does not map directly
to 'pthread_join'. The latter function gets already called by the
destructor of 'Thread_base'. According to the documentation, subsequent
calls of 'pthread_join' for one thread may result in undefined behaviour.
So we use a 'Genode::Lock' on this platform, which is in line with the
other platforms.
Related to #194, #501
The thread ID reported to core was not always initialized prior the RPC
call. The 'startup_lock' ensures that the thread is completely
initialized before this information gets propagated.
This patch alleviates the need for any non-core process to create Unix
domain sockets locally. All sockets used for RPC communication are
created by core and subsequently passed to the other processes via RPC
or the parent interface. The immediate benefit is that no process other
than core needs to access the 'rpath' directory in order to communicate.
However, access to 'rpath' is still needed for accessing dataspaces.
Core creates one socket pair per thread on demand on the first call of
the 'Linux_cpu_session::server_sd()' or 'Linux_cpu_session::client_sd()'
functions. 'Linux_cpu_session' is a Linux-specific extension to the CPU
session interface. In addition to the socket accessors, the extension
provides a mechanism to register the PID/TID of a thread. Those
information were formerly propagated into core along with the thread
name as argument to 'create_thread()'.
Because core creates socket pairs for entrypoints, it needs to know all
threads that are potential entrypoints. For lx_hybrid programs, we
hadn't had propagated any thread information into core, yet. Hence, this
patch also contains the code for registering threads of hybrid
applications at core.
Setting the handler for SIGCHLD to SIG_IGN (ignore) informs the kernel
not to enter the zombie state: (man 2 wait)
POSIX.1-2001 specifies that if the disposition of SIGCHLD is set to
SIG_IGN or the SA_NOCLDWAIT flag is set for SIGCHLD (see
sigaction(2)), then children that terminate do not become zombies
[...]
Fixes#271.
Alexander Boettcher
Martin Stein
Christian Prochaska
Christian Helmuth
Norman Feske
Genode Labs