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
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
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.
