arch/x86/entry/calling.h

Source file repositories/reference/linux-study-clean/arch/x86/entry/calling.h

File Facts

System
Linux kernel
Corpus path
arch/x86/entry/calling.h
Extension
.h
Size
12967 bytes
Lines
490
Domain
Architecture Layer
Bucket
arch/x86
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#include <linux/jump_label.h>
#include <asm/unwind_hints.h>
#include <asm/cpufeatures.h>
#include <asm/page_types.h>
#include <asm/percpu.h>
#include <asm/asm-offsets.h>
#include <asm/processor-flags.h>
#include <asm/ptrace-abi.h>
#include <asm/msr.h>
#include <asm/nospec-branch.h>

/*

 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:
 */

.macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 unwind_hint=1
	.if \save_ret
	pushq	%rsi		/* pt_regs->si */
	movq	8(%rsp), %rsi	/* temporarily store the return address in %rsi */
	movq	%rdi, 8(%rsp)	/* pt_regs->di (overwriting original return address) */
	/* We just clobbered the return address - use the IRET frame for unwinding: */
	UNWIND_HINT_IRET_REGS offset=3*8
	.else
	pushq   %rdi		/* pt_regs->di */
	pushq   %rsi		/* pt_regs->si */
	.endif
	pushq	\rdx		/* pt_regs->dx */
	pushq   \rcx		/* pt_regs->cx */
	pushq   \rax		/* pt_regs->ax */
	pushq   %r8		/* pt_regs->r8 */
	pushq   %r9		/* pt_regs->r9 */
	pushq   %r10		/* pt_regs->r10 */
	pushq   %r11		/* pt_regs->r11 */
	pushq	%rbx		/* pt_regs->rbx */
	pushq	%rbp		/* pt_regs->rbp */
	pushq	%r12		/* pt_regs->r12 */
	pushq	%r13		/* pt_regs->r13 */
	pushq	%r14		/* pt_regs->r14 */
	pushq	%r15		/* pt_regs->r15 */

Annotation

Implementation Notes