x86/asm/entry/64: Use more readable constants

Constants such as SS+8 or SS+8-RIP are mysterious.
In most cases, SS+8 is just meant to be SIZEOF_PTREGS,
SS+8-RIP is RIP's offset in the iret frame.

This patch changes some of these constants to be less
mysterious.

No code changes (verified with objdump).

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy 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: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1d20491384773bd606e23a382fac23ddb49b5178.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 18 insertions, 12 deletions

diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 4a7ceb9789a5..337423590b08 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -88,6 +88,8 @@ For 32-bit we have the following conventions - kernel is built with
 #define RSP             19*8
 #define SS              20*8
 
+#define SIZEOF_PTREGS   21*8
+
         .macro ALLOC_PT_GPREGS_ON_STACK addskip=0
         subq    $15*8+\addskip, %rsp
         CFI_ADJUST_CFA_OFFSET 15*8+\addskip
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 466947770648..858e94e86f5e 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -164,12 +164,12 @@ ENDPROC(native_usergs_sysret64)
  * initial frame state for interrupts (and exceptions without error code)
  */
         .macro INTR_FRAME start=1 offset=0
-        EMPTY_FRAME \start, SS+8+\offset-RIP
-        /*CFI_REL_OFFSET ss, SS+\offset-RIP*/
-        CFI_REL_OFFSET rsp, RSP+\offset-RIP
-        /*CFI_REL_OFFSET rflags, EFLAGS+\offset-RIP*/
-        /*CFI_REL_OFFSET cs, CS+\offset-RIP*/
-        CFI_REL_OFFSET rip, RIP+\offset-RIP
+        EMPTY_FRAME \start, 5*8+\offset
+        /*CFI_REL_OFFSET ss, 4*8+\offset*/
+        CFI_REL_OFFSET rsp, 3*8+\offset
+        /*CFI_REL_OFFSET rflags, 2*8+\offset*/
+        /*CFI_REL_OFFSET cs, 1*8+\offset*/
+        CFI_REL_OFFSET rip, 0*8+\offset
         .endm
 
 /*
@@ -177,7 +177,7 @@ ENDPROC(native_usergs_sysret64)
  * with vector already pushed)
  */
         .macro XCPT_FRAME start=1 offset=0
-        INTR_FRAME \start, RIP+\offset-ORIG_RAX
+        INTR_FRAME \start, 1*8+\offset
         .endm
 
 /*
@@ -645,10 +645,14 @@ END(interrupt)
         cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
         CFI_DEF_CFA_REGISTER    rsi
         pushq %rsi
+        /*
+         * For debugger:
+         * "CFA (Current Frame Address) is the value on stack + offset"
+         */
         CFI_ESCAPE      0x0f /* DW_CFA_def_cfa_expression */, 6, \
-                        0x77 /* DW_OP_breg7 */, 0, \
+                        0x77 /* DW_OP_breg7 (rsp) */, 0, \
                         0x06 /* DW_OP_deref */, \
-                        0x08 /* DW_OP_const1u */, SS+8-RBP, \
+                        0x08 /* DW_OP_const1u */, SIZEOF_PTREGS-RBP, \
                         0x22 /* DW_OP_plus */
         /* We entered an interrupt context - irqs are off: */
         TRACE_IRQS_OFF
@@ -674,7 +678,7 @@ ret_from_intr:
 
         /* Restore saved previous stack */
         popq %rsi
-        CFI_DEF_CFA rsi,SS+8-RBP        /* reg/off reset after def_cfa_expr */
+        CFI_DEF_CFA rsi,SIZEOF_PTREGS-RBP /* reg/off reset after def_cfa_expr */
         /* return code expects complete pt_regs - adjust rsp accordingly: */
         leaq -RBP(%rsi),%rsp
         CFI_DEF_CFA_REGISTER    rsp
@@ -1549,7 +1553,7 @@ first_nmi:
         .rept 5
         pushq_cfi 11*8(%rsp)
         .endr
-        CFI_DEF_CFA_OFFSET SS+8-RIP
+        CFI_DEF_CFA_OFFSET 5*8
 
         /* Everything up to here is safe from nested NMIs */
 
@@ -1577,7 +1581,7 @@ repeat_nmi:
         pushq_cfi -6*8(%rsp)
         .endr
         subq $(5*8), %rsp
-        CFI_DEF_CFA_OFFSET SS+8-RIP
+        CFI_DEF_CFA_OFFSET 5*8
 end_repeat_nmi:
 
         /*