When allocating stack space with an alignment requirement that is larger
than the current stack alignment we need to store a copy of the original
stack pointer in order to be able to restore it later.
If we chose to use another register for this purpose we should not pick
eax/rax since it can be overwritten as a return value.
Signed-off-by: Anton Khirnov <anton@khirnov.net>
%ifnum %1
%if %1 != 0 && required_stack_alignment > STACK_ALIGNMENT
%if %1 > 0
+ ; Reserve an additional register for storing the original stack pointer, but avoid using
+ ; eax/rax for this purpose since it can potentially get overwritten as a return value.
%assign regs_used (regs_used + 1)
+ %if ARCH_X86_64 && regs_used == 7
+ %assign regs_used 8
+ %elif ARCH_X86_64 == 0 && regs_used == 1
+ %assign regs_used 2
+ %endif
%endif
%if ARCH_X86_64 && regs_used < 5 + UNIX64 * 3
; Ensure that we don't clobber any registers containing arguments. For UNIX64 we also preserve r6 (rax)