[PATCH v6 03/28] powerpc/xmon: Move breakpoints to text section

[Jordan Niethe]

On Tue, Apr 28, 2020 at 3:36 PM Christophe Leroy
<christophe.leroy at c-s.fr> wrote:
>
>
>
> Le 28/04/2020 à 07:30, Jordan Niethe a écrit :
> > On Tue, Apr 28, 2020 at 3:20 PM Christophe Leroy
> > <christophe.leroy at c-s.fr> wrote:
> >>
> >>
> >>
> >> Le 28/04/2020 à 03:57, Jordan Niethe a écrit :
> >>> The instructions for xmon's breakpoint are stored bpt_table[] which is in
> >>> the data section. This is problematic as the data section may be marked
> >>> as no execute. Move bpt_table[] to the text section.
> >>>
> >>> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> >>> ---
> >>> v6: - New to series. Was part of the previous patch.
> >>>       - Make BPT_SIZE available in assembly
> >>> ---
> >>>    arch/powerpc/kernel/asm-offsets.c |  8 ++++++++
> >>>    arch/powerpc/xmon/Makefile        |  2 +-
> >>>    arch/powerpc/xmon/xmon.c          |  6 +-----
> >>>    arch/powerpc/xmon/xmon_bpts.S     |  9 +++++++++
> >>>    arch/powerpc/xmon/xmon_bpts.h     | 14 ++++++++++++++
> >>>    5 files changed, 33 insertions(+), 6 deletions(-)
> >>>    create mode 100644 arch/powerpc/xmon/xmon_bpts.S
> >>>    create mode 100644 arch/powerpc/xmon/xmon_bpts.h
> >>>
> >>> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> >>> index c25e562f1cd9..2401f415f423 100644
> >>> --- a/arch/powerpc/kernel/asm-offsets.c
> >>> +++ b/arch/powerpc/kernel/asm-offsets.c
> >>> @@ -70,6 +70,10 @@
> >>>    #include <asm/fixmap.h>
> >>>    #endif
> >>>
> >>> +#ifdef CONFIG_XMON
> >>> +#include "../xmon/xmon_bpts.h"
> >>> +#endif
> >>> +
> >>>    #define STACK_PT_REGS_OFFSET(sym, val)      \
> >>>        DEFINE(sym, STACK_FRAME_OVERHEAD + offsetof(struct pt_regs, val))
> >>>
> >>> @@ -783,5 +787,9 @@ int main(void)
> >>>        DEFINE(VIRT_IMMR_BASE, (u64)__fix_to_virt(FIX_IMMR_BASE));
> >>>    #endif
> >>>
> >>> +#ifdef CONFIG_XMON
> >>> +     DEFINE(BPT_SIZE, BPT_SIZE);
> >>> +#endif
> >>> +
> >>>        return 0;
> >>>    }
> >>> diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> >>> index c3842dbeb1b7..515a13ea6f28 100644
> >>> --- a/arch/powerpc/xmon/Makefile
> >>> +++ b/arch/powerpc/xmon/Makefile
> >>> @@ -21,7 +21,7 @@ endif
> >>>
> >>>    ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
> >>>
> >>> -obj-y                        += xmon.o nonstdio.o spr_access.o
> >>> +obj-y                        += xmon.o nonstdio.o spr_access.o xmon_bpts.o
> >>>
> >>>    ifdef CONFIG_XMON_DISASSEMBLY
> >>>    obj-y                       += ppc-dis.o ppc-opc.o
> >>> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> >>> index a064392df1b8..f7ce3ea8694c 100644
> >>> --- a/arch/powerpc/xmon/xmon.c
> >>> +++ b/arch/powerpc/xmon/xmon.c
> >>> @@ -62,6 +62,7 @@
> >>>
> >>>    #include "nonstdio.h"
> >>>    #include "dis-asm.h"
> >>> +#include "xmon_bpts.h"
> >>>
> >>>    #ifdef CONFIG_SMP
> >>>    static cpumask_t cpus_in_xmon = CPU_MASK_NONE;
> >>> @@ -108,7 +109,6 @@ struct bpt {
> >>>    #define BP_TRAP             2
> >>>    #define BP_DABR             4
> >>>
> >>> -#define NBPTS        256
> >>>    static struct bpt bpts[NBPTS];
> >>>    static struct bpt dabr;
> >>>    static struct bpt *iabr;
> >>> @@ -116,10 +116,6 @@ static unsigned bpinstr = 0x7fe00008;    /* trap */
> >>>
> >>>    #define BP_NUM(bp)  ((bp) - bpts + 1)
> >>>
> >>> -#define BPT_SIZE       (sizeof(unsigned int) * 2)
> >>> -#define BPT_WORDS      (BPT_SIZE / sizeof(unsigned int))
> >>> -static unsigned int bpt_table[NBPTS * BPT_WORDS];
> >>> -
> >>>    /* Prototypes */
> >>>    static int cmds(struct pt_regs *);
> >>>    static int mread(unsigned long, void *, int);
> >>> diff --git a/arch/powerpc/xmon/xmon_bpts.S b/arch/powerpc/xmon/xmon_bpts.S
> >>> new file mode 100644
> >>> index 000000000000..f3ad0ab50854
> >>> --- /dev/null
> >>> +++ b/arch/powerpc/xmon/xmon_bpts.S
> >>> @@ -0,0 +1,9 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +#include <asm/ppc_asm.h>
> >>> +#include <asm/asm-compat.h>
> >>> +#include <asm/asm-offsets.h>
> >>> +#include "xmon_bpts.h"
> >>> +
> >>> +.global bpt_table
> >>> +bpt_table:
> >>> +     .space NBPTS * BPT_SIZE
> >>
> >> No alignment required ? Standard alignment (probably 4 bytes ?) is
> >> acceptable ?
> > No, I'll add a .balign    4 to be sure.
>
> I think it is aligned to 4 by default. My question was to know whether 4
> is enough.
> I see BPT_SIZE is 8, should the alignment be at least 8 ?
At this point each breakpoint entry is two instructions: the
instruction that has been replaced by a breakpoint and a trap
instruction after that. So I think it should be fine aligned to 4. In
the patch that introduces prefixed instructions to the data type, the
alignment changes.
>
> >>
> >>
> >>> diff --git a/arch/powerpc/xmon/xmon_bpts.h b/arch/powerpc/xmon/xmon_bpts.h
> >>> new file mode 100644
> >>> index 000000000000..b7e94375db86
> >>> --- /dev/null
> >>> +++ b/arch/powerpc/xmon/xmon_bpts.h
> >>> @@ -0,0 +1,14 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +#ifndef XMON_BPTS_H
> >>> +#define XMON_BPTS_H
> >>> +
> >>> +#define NBPTS        256
> >>> +#ifndef __ASSEMBLY__
> >>> +#define BPT_SIZE     (sizeof(unsigned int) * 2)
> >>> +#define BPT_WORDS    (BPT_SIZE / sizeof(unsigned int))
> >>> +
> >>> +extern unsigned int bpt_table[NBPTS * BPT_WORDS];
> >>> +
> >>> +#endif /* __ASSEMBLY__ */
> >>> +
> >>> +#endif /* XMON_BPTS_H */
> >>>
> >>
> >> Christophe