this should not be necessary - the invalid bit patterns cannot be
created except through type punning. however, some broken gnu software
is passing them to printf and triggering dangerous stack-smashing, so
let's catch them anyway...
this is a really ugly and backwards function, but its presence will
prevent lots of broken gnulib software from trying to define its own
version of fpurge and thereby failing to build or worse.
per POSIX: The mprotect() function shall change the access protections
to be that specified by prot for those whole pages containing any part
of the address space of the process starting at address addr and
continuing for len bytes.
on the other hand, linux mprotect fails with EINVAL if the base
address and/or length is not page-aligned, so we have to align them
before making the syscall.
this is mostly useless for shared libs (though it could help for
prelink-like purposes); the intended use case is for adding support
for calling the dynamic linker directly to run a program, as in:
./libc.so ./a.out foo
this usage is not yet supported.
basically we temporarily make the library and all its dependencies
part of the global namespace but only for the duration of performing
relocations, then return them to their former state.
some of the code is not yet used, and is in preparation for dlopen
which needs to be able to handle failure loading libraries without
terminating the program.
the use of this test will be much stricter than glibc and other
typical implementations; the environment will not be honored
whatsoever unless the program is confirmed non-suid/sgid by the aux
vector the kernel passed in. no fallback to slow syscall-based
checking is used if the kernel fails to provide the information; we
simply assume the worst (suid) in this case and refuse to honor
environment.
some notes:
- library search path is hard coded
- x86_64 code is untested and may not work
- dlopen/dlsym is not yet implemented
- relocations in read-only memory won't work
this seems to be necessary to make the linker accept the functions in
a shared library (perhaps to generate PLT entries?)
strictly speaking libc-internal asm should not need it. i might clean
that up later.
