based on initial work by rdp, with heavy modifications. some features
including threads are untested because qemu app-level emulation seems
to be broken and I do not have a proper system image for testing.
it's naturally aligned when entered with the kernel argv array, but if
ld.so has been invoked explicitly to run a program, the stack will not
be aligned due to having thrown away argv[0].
since .init and .fini are not .text, the toolchain does not seem to
align them for code by default. this yields random breakage depending
on the object sizes the linker is dealing with.
basically, this version of the code was obtained by starting with
rdp's work from his ellcc source tree, adapting it to musl's build
system and coding style, auditing the bits headers for discrepencies
with kernel definitions or glibc/LSB ABI or large file issues, fixing
up incompatibility with the old binutils from aboriginal linux, and
adding some new special cases to deal with the oddities of sigaction
and pipe syscall interfaces on mips.
at present, minimal test programs work, but some interfaces are broken
or missing. threaded programs probably will not link.
lr must be saved because init/fini-section code from the compiler
clobbers it. this was not a problem when i tested without gcc's
crtbegin/crtend files present, but with them, musl on arm fails to
work (infinite loop in _init).
looks like nik copied these "extra arguments" from the i386 code.
they're not actually arguments there, just 1-byte instructions to
make sure the stack is aligned to 16 bytes after all the other
arguments are pushed. since each push is 8 bytes on x86_64, they
happened to have no effect here, but their presence is confusing and a
minor waste of space.
it does not work; after further consideration, a separate Scrt1.s for
pie really is essential. it would be nice if the unified approach
worked, but the linker fails to generate the correct PLT entries and
instead puts textrels in the main program, which don't work because
the kernel maps the text read-only.
new Scrt1.s will be committed soon in place of this.
this is mainly in hopes of supporting c++ (not yet possible for other
reasons) but will also help applications/libraries which use (and more
often, abuse) the gcc __attribute__((__constructor__)) feature in "C"
code.
x86_64 and arm versions of the new startup asm are untested and may
have minor problems.
this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.
some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.
rofl0r
Richard Pennington
Rich Felker
Nicholas J. Kain