[PATCH 3/3] uprobes/x86: Simplify riprel_{pre,post}_xol() and make them similar

[Oleg Nesterov]

Ignoring the "correction" logic riprel_pre_xol() and riprel_post_xol()
are very similar but look quite differently.

1. Add the "UPROBE_FIX_RIP_AX | UPROBE_FIX_RIP_CX" check at the start
   of riprel_pre_xol(), like the same check in riprel_post_xol().

2. Add the trivial scratch_reg() helper which returns the address of
   scratch register pre_xol/post_xol need to change.

3. Change these functions to use the new helper and avoid copy-and-paste
   under if/else branches.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
 arch/x86/kernel/uprobes.c |   32 +++++++++++++++-----------------
 1 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 9f6aba3..6a9cac1 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -326,22 +326,24 @@ static void riprel_analyze(struct arch_uprobe *auprobe, 
struct insn *insn)
        }
 }
 
+static inline unsigned long *
+scratch_reg(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+       return (auprobe->def.fixups & UPROBE_FIX_RIP_AX) ? &regs->ax : 
&regs->cx;
+}
+
 /*
  * If we're emulating a rip-relative instruction, save the contents
  * of the scratch register and store the target address in that register.
  */
 static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
-       struct uprobe_task *utask = current->utask;
+       if (auprobe->def.fixups & (UPROBE_FIX_RIP_AX | UPROBE_FIX_RIP_CX)) {
+               struct uprobe_task *utask = current->utask;
+               unsigned long *sr = scratch_reg(auprobe, regs);
 
-       if (auprobe->def.fixups & UPROBE_FIX_RIP_AX) {
-               utask->autask.saved_scratch_register = regs->ax;
-               regs->ax = utask->vaddr;
-               regs->ax += auprobe->def.riprel_target;
-       } else if (auprobe->def.fixups & UPROBE_FIX_RIP_CX) {
-               utask->autask.saved_scratch_register = regs->cx;
-               regs->cx = utask->vaddr;
-               regs->cx += auprobe->def.riprel_target;
+               utask->autask.saved_scratch_register = *sr;
+               *sr = utask->vaddr + auprobe->def.riprel_target;
        }
 }
 
@@ -349,14 +351,10 @@ static void riprel_post_xol(struct arch_uprobe *auprobe, 
struct pt_regs *regs,
                                long *correction)
 {
        if (auprobe->def.fixups & (UPROBE_FIX_RIP_AX | UPROBE_FIX_RIP_CX)) {
-               struct arch_uprobe_task *autask;
-
-               autask = &current->utask->autask;
-               if (auprobe->def.fixups & UPROBE_FIX_RIP_AX)
-                       regs->ax = autask->saved_scratch_register;
-               else
-                       regs->cx = autask->saved_scratch_register;
+               struct uprobe_task *utask = current->utask;
+               unsigned long *sr = scratch_reg(auprobe, regs);
 
+               *sr = utask->autask.saved_scratch_register;
                /*
                 * The original instruction includes a displacement, and so
                 * is 4 bytes longer than what we've just single-stepped.
-- 
1.5.5.1

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