Re: [RFC perf/core 03/11] uprobes: Add len argument to uprobe_write_opcode

[Jiri Olsa]

On Thu, Nov 14, 2024 at 03:41:03PM -0800, Andrii Nakryiko wrote:
> On Tue, Nov 5, 2024 at 5:34 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding len argument to uprobe_write_opcode as preparation
> > fo writing longer instructions in following changes.
> 
> typo: for
> 
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  include/linux/uprobes.h |  3 ++-
> >  kernel/events/uprobes.c | 14 ++++++++------
> >  2 files changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> > index 28068f9fcdc1..7d23a4fee6f4 100644
> > --- a/include/linux/uprobes.h
> > +++ b/include/linux/uprobes.h
> > @@ -181,7 +181,8 @@ extern bool is_swbp_insn(uprobe_opcode_t *insn);
> >  extern bool is_trap_insn(uprobe_opcode_t *insn);
> >  extern unsigned long uprobe_get_swbp_addr(struct pt_regs *regs);
> >  extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> > -extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t);
> > +extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > +                              unsigned long vaddr, uprobe_opcode_t *insn, int len);
> 
> is len in sizeof(uprobe_opcode_t) units or in bytes? it would be good
> to make this clearer
> 
> it feels like passing `void *` for insns would be better, tbh...

good catch, it's meant as bytes, uprobe_opcode_t is u8 on x86, but other archs
treat it differently, void * might solve that in this function, will check

thanks,
jirka

> 
> 
> 
> >  extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
> >  extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
> >  extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index e9308649bba3..3e275717789b 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -471,7 +471,7 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
> >   * Return 0 (success) or a negative errno.
> >   */
> >  int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > -                       unsigned long vaddr, uprobe_opcode_t opcode)
> > +                       unsigned long vaddr, uprobe_opcode_t *insn, int len)
> >  {
> >         struct uprobe *uprobe;
> >         struct page *old_page, *new_page;
> > @@ -480,7 +480,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >         bool orig_page_huge = false;
> >         unsigned int gup_flags = FOLL_FORCE;
> >
> > -       is_register = is_swbp_insn(&opcode);
> > +       is_register = is_swbp_insn(insn);
> >         uprobe = container_of(auprobe, struct uprobe, arch);
> >
> >  retry:
> > @@ -491,7 +491,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >         if (IS_ERR(old_page))
> >                 return PTR_ERR(old_page);
> >
> > -       ret = verify_opcode(old_page, vaddr, &opcode);
> > +       ret = verify_opcode(old_page, vaddr, insn);
> >         if (ret <= 0)
> >                 goto put_old;
> >
> > @@ -525,7 +525,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >
> >         __SetPageUptodate(new_page);
> >         copy_highpage(new_page, old_page);
> > -       copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
> > +       copy_to_page(new_page, vaddr, insn, len);
> >
> >         if (!is_register) {
> >                 struct page *orig_page;
> > @@ -582,7 +582,9 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >   */
> >  int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
> >  {
> > -       return uprobe_write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
> > +       uprobe_opcode_t insn = UPROBE_SWBP_INSN;
> > +
> > +       return uprobe_write_opcode(auprobe, mm, vaddr, &insn, UPROBE_SWBP_INSN_SIZE);
> >  }
> >
> >  /**
> > @@ -598,7 +600,7 @@ int __weak
> >  set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
> >  {
> >         return uprobe_write_opcode(auprobe, mm, vaddr,
> > -                       *(uprobe_opcode_t *)&auprobe->insn);
> > +                       (uprobe_opcode_t *)&auprobe->insn, UPROBE_SWBP_INSN_SIZE);
> >  }
> >
> >  /* uprobe should have guaranteed positive refcount */
> > --
> > 2.47.0
> >