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.
- use the generic 'crt0.s' for Linux
- move the read-only '__dso_handle' definition into the '.text' section
- move the '__initial_sp' definition into the '.bss' section
- remove the '_main_utcb' definition
Part of #766.
