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