Re: [PATCH/RESEND] recordmcount: arm: Implement make_nop

[Ard Biesheuvel]

On 19 October 2016 at 00:42, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
> In similar spirit to x86 and arm64 support, add a make_nop_arm()
> to replace calls to mcount with a nop in sections that aren't
> traced.
>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> Acked-by: Rabin Vincent <rabin@xxxxxx>
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> ---
>  scripts/recordmcount.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index 5423a58d1b06..aeb34223167c 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -213,6 +213,59 @@ static int make_nop_x86(void *map, size_t const offset)
>         return 0;
>  }
>
> +static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */
> +static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */

Shouldn't you be taking the difference between BE8 and BE32 into
account here? IIRC, BE8 uses little endian encoding for instructions.

> +static unsigned char *ideal_nop4_arm;
> +
> +static unsigned char bl_mcount_arm_le[4] = { 0xfe, 0xff, 0xff, 0xeb }; /* bl */
> +static unsigned char bl_mcount_arm_be[4] = { 0xeb, 0xff, 0xff, 0xfe }; /* bl */
> +static unsigned char *bl_mcount_arm;
> +
> +static unsigned char push_arm_le[4] = { 0x04, 0xe0, 0x2d, 0xe5 }; /* push {lr} */
> +static unsigned char push_arm_be[4] = { 0xe5, 0x2d, 0xe0, 0x04 }; /* push {lr} */
> +static unsigned char *push_arm;
> +
> +static unsigned char ideal_nop2_thumb_le[2] = { 0x00, 0xbf }; /* nop */
> +static unsigned char ideal_nop2_thumb_be[2] = { 0xbf, 0x00 }; /* nop */
> +static unsigned char *ideal_nop2_thumb;
> +
> +static unsigned char push_bl_mcount_thumb_le[6] = { 0x00, 0xb5, 0xff, 0xf7, 0xfe, 0xff }; /* push {lr}, bl */
> +static unsigned char push_bl_mcount_thumb_be[6] = { 0xb5, 0x00, 0xf7, 0xff, 0xff, 0xfe }; /* push {lr}, bl */
> +static unsigned char *push_bl_mcount_thumb;
> +
> +static int make_nop_arm(void *map, size_t const offset)
> +{
> +       char *ptr;
> +       int cnt = 1;
> +       int nop_size;
> +       size_t off = offset;
> +
> +       ptr = map + offset;
> +       if (memcmp(ptr, bl_mcount_arm, 4) == 0) {
> +               if (memcmp(ptr - 4, push_arm, 4) == 0) {
> +                       off -= 4;
> +                       cnt = 2;
> +               }
> +               ideal_nop = ideal_nop4_arm;
> +               nop_size = 4;
> +       } else if (memcmp(ptr - 2, push_bl_mcount_thumb, 6) == 0) {
> +               cnt = 3;
> +               nop_size = 2;
> +               off -= 2;
> +               ideal_nop = ideal_nop2_thumb;
> +       } else
> +               return -1;
> +
> +       /* Convert to nop */
> +       ulseek(fd_map, off, SEEK_SET);
> +
> +       do {
> +               uwrite(fd_map, ideal_nop, nop_size);
> +       } while (--cnt > 0);
> +
> +       return 0;
> +}
> +
>  static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
>  static int make_nop_arm64(void *map, size_t const offset)
>  {
> @@ -430,6 +483,11 @@ do_file(char const *const fname)
>                         w2 = w2rev;
>                         w8 = w8rev;
>                 }
> +               ideal_nop4_arm = ideal_nop4_arm_le;
> +               bl_mcount_arm = bl_mcount_arm_le;
> +               push_arm = push_arm_le;
> +               ideal_nop2_thumb = ideal_nop2_thumb_le;
> +               push_bl_mcount_thumb = push_bl_mcount_thumb_le;
>                 break;
>         case ELFDATA2MSB:
>                 if (*(unsigned char const *)&endian != 0) {
> @@ -438,6 +496,11 @@ do_file(char const *const fname)
>                         w2 = w2rev;
>                         w8 = w8rev;
>                 }
> +               ideal_nop4_arm = ideal_nop4_arm_be;
> +               bl_mcount_arm = bl_mcount_arm_be;
> +               push_arm = push_arm_be;
> +               ideal_nop2_thumb = ideal_nop2_thumb_be;
> +               push_bl_mcount_thumb = push_bl_mcount_thumb_be;
>                 break;
>         }  /* end switch */
>         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
> @@ -463,6 +526,8 @@ do_file(char const *const fname)
>                 break;
>         case EM_ARM:     reltype = R_ARM_ABS32;
>                          altmcount = "__gnu_mcount_nc";
> +                        make_nop = make_nop_arm;
> +                        rel_type_nop = R_ARM_NONE;
>                          break;
>         case EM_AARCH64:
>                         reltype = R_AARCH64_ABS64;
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
>
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