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Commit e90e147c authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar
Browse files

x86/asm/entry/64: Fix comments 



 - Misleading and slightly incorrect comments in "struct pt_regs" are
   fixed (four instances).

 - Fix incorrect comment atop EMPTY_FRAME macro.

 - Explain in more detail what we do with stack layout during hw interrupt.

 - Correct comments about "partial stack frame" which are no longer
   true.

Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1423778052-21038-3-git-send-email-dvlasenk@redhat.com
Link: http://lkml.kernel.org/r/e1f4429c491fe6ceeddb879dea2786e0f8920f9c.1424989793.git.luto@amacapital.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 76f5df43

arch/x86/include/asm/ptrace.h

+10 −3
Original line number Diff line number Diff line
@@ -31,13 +31,17 @@ struct pt_regs { 
#else /* __i386__ */



struct pt_regs {

/*

 * 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".

 */

	unsigned long r15;

	unsigned long r14;

	unsigned long r13;

	unsigned long r12;

	unsigned long bp;

	unsigned long bx;

/* arguments: non interrupts/non tracing syscalls only save up to here*/

/* These regs are callee-clobbered. Always saved on kernel entry. */

	unsigned long r11;

	unsigned long r10;

	unsigned long r9;
@@ -47,9 +51,12 @@ struct pt_regs { 
	unsigned long dx;

	unsigned long si;

	unsigned long di;

/*

 * On syscall entry, this is syscall#. On CPU exception, this is error code.

 * On hw interrupt, it's IRQ number:

 */

	unsigned long orig_ax;

/* end of arguments */

/* cpu exception frame or undefined */

/* Return frame for iretq */

	unsigned long ip;

	unsigned long cs;

	unsigned long flags;

arch/x86/include/uapi/asm/ptrace-abi.h

+11 −4
Original line number Diff line number Diff line
@@ -25,13 +25,17 @@ 
#else /* __i386__ */



#if defined(__ASSEMBLY__) || defined(__FRAME_OFFSETS)

/*

 * 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

#define R14 8

#define R13 16

#define R12 24

#define RBP 32

#define RBX 40

/* arguments: interrupts/non tracing syscalls only save up to here*/

/* These regs are callee-clobbered. Always saved on kernel entry. */

#define R11 48

#define R10 56

#define R9 64
@@ -41,9 +45,12 @@ 
#define RDX 96

#define RSI 104

#define RDI 112

#define ORIG_RAX 120       /* = ERROR */

/* end of arguments */

/* cpu exception frame or undefined in case of fast syscall. */

/*

 * On syscall entry, this is syscall#. On CPU exception, this is error code.

 * On hw interrupt, it's IRQ number:

 */

#define ORIG_RAX 120

/* Return frame for iretq */

#define RIP 128

#define CS 136

#define EFLAGS 144

arch/x86/include/uapi/asm/ptrace.h

+10 −3
Original line number Diff line number Diff line
@@ -41,13 +41,17 @@ struct pt_regs { 
#ifndef __KERNEL__



struct pt_regs {

/*

 * 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".

 */

	unsigned long r15;

	unsigned long r14;

	unsigned long r13;

	unsigned long r12;

	unsigned long rbp;

	unsigned long rbx;

/* arguments: non interrupts/non tracing syscalls only save up to here*/

/* These regs are callee-clobbered. Always saved on kernel entry. */

	unsigned long r11;

	unsigned long r10;

	unsigned long r9;
@@ -57,9 +61,12 @@ struct pt_regs { 
	unsigned long rdx;

	unsigned long rsi;

	unsigned long rdi;

/*

 * On syscall entry, this is syscall#. On CPU exception, this is error code.

 * On hw interrupt, it's IRQ number:

 */

	unsigned long orig_rax;

/* end of arguments */

/* cpu exception frame or undefined */

/* Return frame for iretq */

	unsigned long rip;

	unsigned long cs;

	unsigned long eflags;

arch/x86/kernel/entry_64.S

+12 −6
Original line number Diff line number Diff line
@@ -14,9 +14,6 @@ 
 * NOTE: This code handles signal-recognition, which happens every time

 * after an interrupt and after each system call.

 *

 * Normal syscalls and interrupts don't save a full stack frame, this is

 * only done for syscall tracing, signals or fork/exec et.al.

 *

 * A note on terminology:

 * - top of stack: Architecture defined interrupt frame from SS to RIP

 * at the top of the kernel process stack.
@@ -151,7 +148,7 @@ ENDPROC(native_usergs_sysret64) 
	.endm



/*

 * initial frame state for interrupts (and exceptions without error code)

 * empty frame

 */

	.macro EMPTY_FRAME start=1 offset=0

	.if \start
@@ -379,7 +376,7 @@ tracesys_phase2: 
	call syscall_trace_enter_phase2



	/*

	 * Reload arg registers from stack in case ptrace changed them.

	 * Reload registers from stack in case ptrace changed them.

	 * We don't reload %rax because syscall_trace_entry_phase2() returned

	 * the value it wants us to use in the table lookup.

	 */
@@ -629,6 +626,13 @@ END(interrupt) 
/* 0(%rsp): ~(interrupt number) */

	.macro interrupt func

	cld

	/*

	 * Since nothing in interrupt handling code touches r12...r15 members

	 * of "struct pt_regs", and since interrupts can nest, we can save

	 * four stack slots and simultaneously provide

	 * an unwind-friendly stack layout by saving "truncated" pt_regs

	 * exactly up to rbp slot, without these members.

	 */

	ALLOC_PT_GPREGS_ON_STACK -RBP

	SAVE_C_REGS -RBP

	/* this goes to 0(%rsp) for unwinder, not for saving the value: */
@@ -641,6 +645,7 @@ END(interrupt) 
	SWAPGS

1:

	/*

	 * Save previous stack pointer, optionally switch to interrupt stack.

	 * irq_count is used to check if a CPU is already on an interrupt stack

	 * or not. While this is essentially redundant with preempt_count it is

	 * a little cheaper to use a separate counter in the PDA (short of
@@ -681,6 +686,7 @@ ret_from_intr: 
	/* Restore saved previous stack */

	popq %rsi

	CFI_DEF_CFA rsi,SS+8-RBP	/* reg/off reset after def_cfa_expr */

	/* return code expects complete pt_regs - adjust rsp accordingly: */

	leaq ARGOFFSET-RBP(%rsi), %rsp

	CFI_DEF_CFA_REGISTER	rsp

	CFI_ADJUST_CFA_OFFSET	RBP-ARGOFFSET
@@ -692,7 +698,7 @@ exit_intr: 


	/* Interrupt came from user space */

	/*

	 * Has a correct top of stack, but a partial stack frame

	 * Has a correct top of stack.

	 * %rcx: thread info. Interrupts off.

	 */

retint_with_reschedule: