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diff --git a/kernel/arch/x86/entry/calling.h b/kernel/arch/x86/entry/calling.h
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+/*
+
+ x86 function call convention, 64-bit:
+ -------------------------------------
+ arguments | callee-saved | extra caller-saved | return
+ [callee-clobbered] | | [callee-clobbered] |
+ ---------------------------------------------------------------------------
+ rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**]
+
+ ( rsp is obviously invariant across normal function calls. (gcc can 'merge'
+ functions when it sees tail-call optimization possibilities) rflags is
+ clobbered. Leftover arguments are passed over the stack frame.)
+
+ [*] In the frame-pointers case rbp is fixed to the stack frame.
+
+ [**] for struct return values wider than 64 bits the return convention is a
+ bit more complex: up to 128 bits width we return small structures
+ straight in rax, rdx. For structures larger than that (3 words or
+ larger) the caller puts a pointer to an on-stack return struct
+ [allocated in the caller's stack frame] into the first argument - i.e.
+ into rdi. All other arguments shift up by one in this case.
+ Fortunately this case is rare in the kernel.
+
+For 32-bit we have the following conventions - kernel is built with
+-mregparm=3 and -freg-struct-return:
+
+ x86 function calling convention, 32-bit:
+ ----------------------------------------
+ arguments | callee-saved | extra caller-saved | return
+ [callee-clobbered] | | [callee-clobbered] |
+ -------------------------------------------------------------------------
+ eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**]
+
+ ( here too esp is obviously invariant across normal function calls. eflags
+ is clobbered. Leftover arguments are passed over the stack frame. )
+
+ [*] In the frame-pointers case ebp is fixed to the stack frame.
+
+ [**] We build with -freg-struct-return, which on 32-bit means similar
+ semantics as on 64-bit: edx can be used for a second return value
+ (i.e. covering integer and structure sizes up to 64 bits) - after that
+ it gets more complex and more expensive: 3-word or larger struct returns
+ get done in the caller's frame and the pointer to the return struct goes
+ into regparm0, i.e. eax - the other arguments shift up and the
+ function's register parameters degenerate to regparm=2 in essence.
+
+*/
+
+#ifdef CONFIG_X86_64
+
+/*
+ * 64-bit system call stack frame layout defines and helpers,
+ * for assembly code:
+ */
+
+/* The layout forms the "struct pt_regs" on the stack: */
+/*
+ * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
+ * unless syscall needs a complete, fully filled "struct pt_regs".
+ */
+#define R15 0*8
+#define R14 1*8
+#define R13 2*8
+#define R12 3*8
+#define RBP 4*8
+#define RBX 5*8
+/* These regs are callee-clobbered. Always saved on kernel entry. */
+#define R11 6*8
+#define R10 7*8
+#define R9 8*8
+#define R8 9*8
+#define RAX 10*8
+#define RCX 11*8
+#define RDX 12*8
+#define RSI 13*8
+#define RDI 14*8
+/*
+ * On syscall entry, this is syscall#. On CPU exception, this is error code.
+ * On hw interrupt, it's IRQ number:
+ */
+#define ORIG_RAX 15*8
+/* Return frame for iretq */
+#define RIP 16*8
+#define CS 17*8
+#define EFLAGS 18*8
+#define RSP 19*8
+#define SS 20*8
+
+#define SIZEOF_PTREGS 21*8
+
+ .macro ALLOC_PT_GPREGS_ON_STACK addskip=0
+ addq $-(15*8+\addskip), %rsp
+ .endm
+
+ .macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8910=1 r11=1
+ .if \r11
+ movq %r11, 6*8+\offset(%rsp)
+ .endif
+ .if \r8910
+ movq %r10, 7*8+\offset(%rsp)
+ movq %r9, 8*8+\offset(%rsp)
+ movq %r8, 9*8+\offset(%rsp)
+ .endif
+ .if \rax
+ movq %rax, 10*8+\offset(%rsp)
+ .endif
+ .if \rcx
+ movq %rcx, 11*8+\offset(%rsp)
+ .endif
+ movq %rdx, 12*8+\offset(%rsp)
+ movq %rsi, 13*8+\offset(%rsp)
+ movq %rdi, 14*8+\offset(%rsp)
+ .endm
+ .macro SAVE_C_REGS offset=0
+ SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1
+ .endm
+ .macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0
+ SAVE_C_REGS_HELPER \offset, 0, 0, 1, 1
+ .endm
+ .macro SAVE_C_REGS_EXCEPT_R891011
+ SAVE_C_REGS_HELPER 0, 1, 1, 0, 0
+ .endm
+ .macro SAVE_C_REGS_EXCEPT_RCX_R891011
+ SAVE_C_REGS_HELPER 0, 1, 0, 0, 0
+ .endm
+ .macro SAVE_C_REGS_EXCEPT_RAX_RCX_R11
+ SAVE_C_REGS_HELPER 0, 0, 0, 1, 0
+ .endm
+
+ .macro SAVE_EXTRA_REGS offset=0
+ movq %r15, 0*8+\offset(%rsp)
+ movq %r14, 1*8+\offset(%rsp)
+ movq %r13, 2*8+\offset(%rsp)
+ movq %r12, 3*8+\offset(%rsp)
+ movq %rbp, 4*8+\offset(%rsp)
+ movq %rbx, 5*8+\offset(%rsp)
+ .endm
+
+ .macro RESTORE_EXTRA_REGS offset=0
+ movq 0*8+\offset(%rsp), %r15
+ movq 1*8+\offset(%rsp), %r14
+ movq 2*8+\offset(%rsp), %r13
+ movq 3*8+\offset(%rsp), %r12
+ movq 4*8+\offset(%rsp), %rbp
+ movq 5*8+\offset(%rsp), %rbx
+ .endm
+
+ .macro ZERO_EXTRA_REGS
+ xorl %r15d, %r15d
+ xorl %r14d, %r14d
+ xorl %r13d, %r13d
+ xorl %r12d, %r12d
+ xorl %ebp, %ebp
+ xorl %ebx, %ebx
+ .endm
+
+ .macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1
+ .if \rstor_r11
+ movq 6*8(%rsp), %r11
+ .endif
+ .if \rstor_r8910
+ movq 7*8(%rsp), %r10
+ movq 8*8(%rsp), %r9
+ movq 9*8(%rsp), %r8
+ .endif
+ .if \rstor_rax
+ movq 10*8(%rsp), %rax
+ .endif
+ .if \rstor_rcx
+ movq 11*8(%rsp), %rcx
+ .endif
+ .if \rstor_rdx
+ movq 12*8(%rsp), %rdx
+ .endif
+ movq 13*8(%rsp), %rsi
+ movq 14*8(%rsp), %rdi
+ .endm
+ .macro RESTORE_C_REGS
+ RESTORE_C_REGS_HELPER 1,1,1,1,1
+ .endm
+ .macro RESTORE_C_REGS_EXCEPT_RAX
+ RESTORE_C_REGS_HELPER 0,1,1,1,1
+ .endm
+ .macro RESTORE_C_REGS_EXCEPT_RCX
+ RESTORE_C_REGS_HELPER 1,0,1,1,1
+ .endm
+ .macro RESTORE_C_REGS_EXCEPT_R11
+ RESTORE_C_REGS_HELPER 1,1,0,1,1
+ .endm
+ .macro RESTORE_C_REGS_EXCEPT_RCX_R11
+ RESTORE_C_REGS_HELPER 1,0,0,1,1
+ .endm
+
+ .macro REMOVE_PT_GPREGS_FROM_STACK addskip=0
+ subq $-(15*8+\addskip), %rsp
+ .endm
+
+ .macro icebp
+ .byte 0xf1
+ .endm
+
+#else /* CONFIG_X86_64 */
+
+/*
+ * For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These
+ * are different from the entry_32.S versions in not changing the segment
+ * registers. So only suitable for in kernel use, not when transitioning
+ * from or to user space. The resulting stack frame is not a standard
+ * pt_regs frame. The main use case is calling C code from assembler
+ * when all the registers need to be preserved.
+ */
+
+ .macro SAVE_ALL
+ pushl %eax
+ pushl %ebp
+ pushl %edi
+ pushl %esi
+ pushl %edx
+ pushl %ecx
+ pushl %ebx
+ .endm
+
+ .macro RESTORE_ALL
+ popl %ebx
+ popl %ecx
+ popl %edx
+ popl %esi
+ popl %edi
+ popl %ebp
+ popl %eax
+ .endm
+
+#endif /* CONFIG_X86_64 */
+