[PATCH v12 15/37] x86/ptrace: Cleanup the definition of the pt_regs structure

Xin Li
2023-10-03T06:54:55Z

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

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
arch/x86/entry/vsyscall/vsyscall_64.c | 2 +-
arch/x86/include/asm/ptrace.h | 44 +++++++++++++++++++--------
arch/x86/kernel/process_64.c | 2 +-
3 files changed, 33 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..f08ea073edd6 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 +79,34 @@ 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 {
+ u64 csx; // The full 64-bit data slot containing CS
+ u16 cs; // CS selector
+ };
+
unsigned long flags;
unsigned long sp;
- unsigned long ss;
-/* top of stack page */
+
+ union {
+ u64 ssx; // The full 64-bit data slot containing SS
+ u16 ss; // SS selector
+ };
+
+ /*
+ * 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 33b268747bb7..0f78b58021bb 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);
--
2.34.1