Re: [PATCH v2] LoongArch: KGDB: Rework arch_kgdb_breakpoint() implementation

[Jinyang He]

On 2025-03-24 12:09, Huacai Chen wrote:

> Hi, Jinyang,
>
> On Mon, Mar 24, 2025 at 9:42 AM Jinyang He <hejinyang@xxxxxxxxxxx> wrote:
> > On 2025-03-22 20:51, Huacai Chen wrote:
> >
> > > Hi, Tiezhu & Jinyang,
> > >
> > > On Fri, Mar 21, 2025 at 10:11 PM WangYuli <wangyuli@xxxxxxxxxxxxx> wrote:
> > > > The arch_kgdb_breakpoint() function defines the kgdb_breakinst
> > > > symbol using inline assembly.
> > > >
> > > > There's a potential issue where the compiler might inline
> > > > arch_kgdb_breakpoint(), which would then define the kgdb_breakinst
> > > > symbol multiple times, leading to a linker error.
> > > >
> > > > To prevent this, declare arch_kgdb_breakpoint() as noline.
> > > >
> > > > Fix follow error with LLVM-19 *only* when LTO_CLANG_FULL:
> > > >       LD      vmlinux.o
> > > >     ld.lld-19: error: ld-temp.o <inline asm>:3:1: symbol 'kgdb_breakinst' is already defined
> > > >     kgdb_breakinst: break 2
> > > >     ^
> > > >
> > > > Additionally, remove "nop" here because it's meaningless for LoongArch
> > > > here.
> > > >
> > > > Fixes: e14dd076964e ("LoongArch: Add basic KGDB & KDB support")
> > > > Co-developed-by: Winston Wen <wentao@xxxxxxxxxxxxx>
> > > > Signed-off-by: Winston Wen <wentao@xxxxxxxxxxxxx>
> > > > Co-developed-by: Wentao Guan <guanwentao@xxxxxxxxxxxxx>
> > > > Signed-off-by: Wentao Guan <guanwentao@xxxxxxxxxxxxx>
> > > > Co-developed-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > > > Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > > > Tested-by: Yuli Wang <wangyuli@xxxxxxxxxxxxx>
> > > > Tested-by: Binbin Zhou <zhoubinbin@xxxxxxxxxxx>
> > > > Signed-off-by: Yuli Wang <wangyuli@xxxxxxxxxxxxx>
> > > > ---
> > > > Changelog:
> > > >    *v1->v2:
> > > >       1. Drop the nop which is no effect for LoongArch here.
> > > >       2. Add "STACK_FRAME_NON_STANDARD" for arch_kgdb_breakpoint() to
> > > > avoid the objtool warning.
> > > > ---
> > > >    arch/loongarch/kernel/kgdb.c | 4 ++--
> > > >    1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/loongarch/kernel/kgdb.c b/arch/loongarch/kernel/kgdb.c
> > > > index 445c452d72a7..38bd0561d7d5 100644
> > > > --- a/arch/loongarch/kernel/kgdb.c
> > > > +++ b/arch/loongarch/kernel/kgdb.c
> > > > @@ -224,13 +224,13 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc)
> > > >           regs->csr_era = pc;
> > > >    }
> > > >
> > > > -void arch_kgdb_breakpoint(void)
> > > > +noinline void arch_kgdb_breakpoint(void)
> > > >    {
> > > >           __asm__ __volatile__ (                  \
> > > >                   ".globl kgdb_breakinst\n\t"     \
> > > > -               "nop\n"                         \
> > > >                   "kgdb_breakinst:\tbreak 2\n\t"); /* BRK_KDB = 2 */
> > > >    }
> > > > +STACK_FRAME_NON_STANDARD(arch_kgdb_breakpoint);
> > > Is there a better solution than STACK_FRAME_NON_STANDARD()? In the
> > > past we can use annotate_reachable() in arch_kgdb_breakpoint(), but
> > > annotate_reachable() is no longer exist.
> > Maybe we can parse the imm-code of `break` and set diffrent insn_type in
> > objtool.
> > The BRK_KDB imply the PC will go head, while the BRK_BUG imply PC stop.
> > (arch/loongarch/include/uapi/asm/break.h)
> >
> > Tiezhu, how do you think?
> Touching objtool may be a little complicated, is ANNOTATE_REACHABLE()
> the successor of annotate_reachable()? I tried
> ANNOTATE_REACHABLE(kgdb_breakinst) but there was still a warning.
Should it annotate to the next insn of `break`?
Like,

    kgdb_breakinst:
    break 2
    another_label:

ANNOTATE_REACHABLE(another_label)

Jinyang
> Huacai
>
> > > Huacai
> > >
> > > >    /*
> > > >     * Calls linux_debug_hook before the kernel dies. If KGDB is enabled,
> > > > --
> > > > 2.49.0