[PATCH v13 13/35] x86/ptrace: Cleanup the definition of the pt_regs structure

[Xin Li <xin3.li@xxxxxxxxx>]

struct pt_regs is hard to read because the member or section related
comments are not aligned with the members.

The 'cs' and 'ss' members of pt_regs are type of 'unsigned long' while
in reality they are only 16-bit wide. This works so far as the
remaining space is unused, but FRED will use the remaining bits for
other purposes.

To prepare for FRED:

  - Cleanup the formatting
  - Convert 'cs' and 'ss' to u16 and embed them into an union
    with a u64
  - Fixup the related printk() format strings

Originally-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Change since v12:
* Put comments ontop, not on the side (Borislav Petkov).
---
 arch/x86/entry/vsyscall/vsyscall_64.c |  2 +-
 arch/x86/include/asm/ptrace.h         | 48 +++++++++++++++++++--------
 arch/x86/kernel/process_64.c          |  2 +-
 3 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c 
b/arch/x86/entry/vsyscall/vsyscall_64.c
index e0ca8120aea8..a3c0df11d0e6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -76,7 +76,7 @@ static void warn_bad_vsyscall(const char *level, struct 
pt_regs *regs,
        if (!show_unhandled_signals)
                return;
 
-       printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx 
di:%lx\n",
+       printk_ratelimited("%s%s[%d] %s ip:%lx cs:%x sp:%lx ax:%lx si:%lx 
di:%lx\n",
                           level, current->comm, task_pid_nr(current),
                           message, regs->ip, regs->cs,
                           regs->sp, regs->ax, regs->si, regs->di);
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index f4db78b09c8f..b268cd2a2d01 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -57,17 +57,19 @@ 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".
- */
+       /*
+        * 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;
-/* These regs are callee-clobbered. Always saved on kernel entry. */
+
+       /* These regs are callee-clobbered. Always saved on kernel entry. */
        unsigned long r11;
        unsigned long r10;
        unsigned long r9;
@@ -77,18 +79,38 @@ 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:
- */
+
+       /*
+        * orig_ax is used on entry for:
+        * - the syscall number (syscall, sysenter, int80)
+        * - error_code stored by the CPU on traps and exceptions
+        * - the interrupt number for device interrupts
+        */
        unsigned long orig_ax;
-/* Return frame for iretq */
+
+       /* The IRETQ return frame starts here */
        unsigned long ip;
-       unsigned long cs;
+
+       union {
+               /* The full 64-bit data slot containing CS */
+               u64             csx;
+               /* CS selector */
+               u16             cs;
+       };
+
        unsigned long flags;
        unsigned long sp;
-       unsigned long ss;
-/* top of stack page */
+
+       union {
+               /* The full 64-bit data slot containing SS */
+               u64             ssx;
+               /* SS selector */
+               u16             ss;
+       };
+
+       /*
+        * Top of stack on IDT systems.
+        */
 };
 
 #endif /* !__i386__ */
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 1553e19904e0..b924477c5ba8 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -117,7 +117,7 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode 
mode,
 
        printk("%sFS:  %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
               log_lvl, fs, fsindex, gs, gsindex, shadowgs);
-       printk("%sCS:  %04lx DS: %04x ES: %04x CR0: %016lx\n",
+       printk("%sCS:  %04x DS: %04x ES: %04x CR0: %016lx\n",
                log_lvl, regs->cs, ds, es, cr0);
        printk("%sCR2: %016lx CR3: %016lx CR4: %016lx\n",
                log_lvl, cr2, cr3, cr4);
-- 
2.43.0