This patch implements 'execve' in Genode's libc.
The mechanism relies on the dynamic linker's ability to replace the
loaded binary while keeping crucial libraries - in particular the libc -
intact. The state outside the libc is wiped. For this reason, all libc
internal state needed beyond the 'execve' call must be allocated on a
heap separate from the application-owned malloc heap. E.g.,
libc-internal file-descriptor objects must not be allocated or refer to
any memory object allocated from the malloc heap.
Issue #3481
The allocation of regions within the linker area is normally left to the
best-fit 'Allocator_avl', which happens to populate the linker area
starting with the binary followed by all loaded libraried with no gaps
in between.
When replacing the binary during execve, however, we need to ensure that
the new binary does not conflict with any library that stays resident
during execve. This patch tweaks the linker's region allocation scheme
such that these libraries are placed at the end of the linker area.
Issue #3481
This patch extends the interface of the dynamic linker with the ability
to replace the running binary executable by another one. It is
designated for the implementation of execve. The interface consists of
two new functions.
'Dynamic_linker::keep' marks the specified shared object as unloadable.
This can be used to pin a set of libraries (i.e., the libc) within the
local address space while replacing the binary and other higher-level
libraries.
'Dynamic_linker::respawn' unloads the current binary, loads the one
specifed as first argument, and looks up the entry point symbol of the
new binary, which would be "main" for POSIX programs.
In addition to implementing the new interface, the patch adjusts the
linker at various places that previously assumed the binary to be
constant over runtime.
Issue #3481
This patch is a follow-up commit for "ld: load dynamic linker at static
address on Linux". It suppresses the stderr output of 'dd' when marking
the ELF binary as executable.
Issue #3479
This patch enables the fork.run script to run on base-linux. It should
be regarded as an interim solution, however, because the randomization
performed by the Linux kernel may still - by chance - produce a
situation where one of the libc's malloc heap regions intersects with
another dataspace dynamically attached to the child.
The better solution would be to make the 'Region_map_mmap'
implementation not depend on the kernel's allocation policy by using a
locally implemented allocator.
Issue #3478
This patch extends the fork test with explicit checks for the cloned
content of the heap and RW segment as well as the seek position of an
open file descriptor. It adds the new libports/run/fork.run script
that exercises the fork mechanism implemented by the libc. It is based
on noux_fork.run, which tests the mechansim provided by noux. The
test program has been moved from ports to libports.
Issue #3478
The libc already supports the configuration of 'stdin', 'stdout', and
'stderr' using '<libc>' config attributes. This patch equips the libc
with the additional ability to pre-initialize any other file descriptor.
A file descriptor is configured as follows:
<config>
...
<libc ...>
<fd id="3" path="/dev/log" writeable="yes" readable="no" seek="10"/>
...
</libc>
</config>
Furthermore, this patch moves the FD initialization code from the VFS
plugin to the libc kernel initialization because opening the FDs
depends on 'malloc' ('strdup'), which should not be used at early
'Libc::Kernel' initialization time.
Issue #3478
This patch replaces the former use of an Allocator_avl with the Id_space
utility, which is safer to use and allows for the iteration of all
elements. The iteration over open file descriptors is needed for
implementing 'fork'.
Issue #3478
The new 'Heap::for_each_region' method provides information about the
heap's used virtual-memory regions. This method allows for the
mirroring of the heap state as needed by 'fork'.
Issue #3478
By specifying the config attribute 'check_ctors="no"', the dynamic
linker won't abort the program on a missing call of
'Env::exec_static_constructors'. This is the case for forked programs
where the ctors were already executed by the forking program prior the
fork operation.
Issue #3478
This patch enhances the 'base/shared_object.h' interface of the dynamic
linker with the function 'for_each_loaded_object', which allows the
caller to obtain information about the currently loaded binary and
shared libraries.
The new interface is a base mechanism needed for implementing 'fork' in
the libc.
Issue #3478
By using Genode::strncpy instead of the libc's strncpy, we cannot end up
in the situation where the result lacks the zero termination (where the
number of charactors equals the destination buffer size).
This patch handles the case where a PD's cap quota becomes exhausted
on the attempt to transfer caps via 'Env::pd().transfer_quota'. The
solution mirrors the existing code for RAM quota.
Prior this patch, the 'transfer_quota' operation would trigger an
'Out_of_caps' exception.
These are time-type conversion functions (including leap years and
seconds) taken from musl-libc git rev
c82d3bada30cb27e14abda7859da5d2e784830ff with some adaptions. Musl is
licensed under permissive MIT license.
Issue #3450
A client may register a signal handler to be notified whenever the
RTC value was changed, i.e., a mis-configured clock was synchronized,
by calling 'set_sigh()'.
Issue #3450
