Re: [PATCH 30/78] ARM: aarch64: Add relocation support

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Fri, Mar 16, 2018 at 5:53 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> This adds aarch64 support for relocating binaries linked with -pie.
>
> Support is integrated into the already exisiting
> relocate_to_current_adr() function which is now used for both arm32
> and aarch64.
>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>


Sascha:

Two small suggestions w.r.t. this patch:

 - I'd consider changing the code of relocate_to_current_adr() such
that AARCH64 specific codepaths are not taken on ARM32 (via IS_ENABLED
check or something similar)

 - I've always wanted to fix the original code to use Elf32_rel type
instead of magic hard-coded offsets, so depending on your
willingness/time-budget, maybe now would be a good time to do that as
well as use Elf64_rela for AARCH64?

Thanks,
Andrey Smirnov

> ---
>  arch/arm/cpu/common.c    | 38 ++++++++++++++++++++++++-------
>  arch/arm/cpu/setupc_64.S | 58 ++++++++++++++++++++++++++++++++++++++++++++++++
>  common/Kconfig           |  2 +-
>  3 files changed, 89 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm/cpu/common.c b/arch/arm/cpu/common.c
> index 3766116d97..c317e502d0 100644
> --- a/arch/arm/cpu/common.c
> +++ b/arch/arm/cpu/common.c
> @@ -24,39 +24,61 @@
>  #include <asm-generic/memory_layout.h>
>  #include <asm/sections.h>
>  #include <asm/cache.h>
> +#include <debug_ll.h>
> +
> +#define R_ARM_RELATIVE 23
> +#define R_AARCH64_RELATIVE 1027
>
>  /*
>   * relocate binary to the currently running address
>   */
>  void relocate_to_current_adr(void)
>  {
> -       unsigned long offset;
> +       unsigned long offset, offset_var;
>         unsigned long *dstart, *dend, *dynsym, *dynend;
>
>         /* Get offset between linked address and runtime address */
>         offset = get_runtime_offset();
> +       offset_var = global_variable_offset();
>
> -       dstart = (void *)__rel_dyn_start + offset;
> -       dend = (void *)__rel_dyn_end + offset;
> +       dstart = (void *)__rel_dyn_start + offset_var;
> +       dend = (void *)__rel_dyn_end + offset_var;
>
> -       dynsym = (void *)__dynsym_start + offset;
> -       dynend = (void *)__dynsym_end + offset;
> +       dynsym = (void *)__dynsym_start + offset_var;
> +       dynend = (void *)__dynsym_end + offset_var;
>
>         while (dstart < dend) {
>                 unsigned long *fixup = (unsigned long *)(*dstart + offset);
>                 unsigned long type = *(dstart + 1);
> +               int add;
> +
> +               if (ELF64_R_TYPE(type) == R_AARCH64_RELATIVE) {
> +                       unsigned long addend = *(dstart + 2);
>
> -               if ((type & 0xff) == 0x17) {
> +                       *fixup = addend + offset;
> +
> +                       add = 3;
> +               } else if (ELF32_R_TYPE(type) == R_ARM_RELATIVE) {
>                         *fixup = *fixup + offset;
> -               } else {
> +
> +                       add = 2;
> +               } else if (ELF32_R_TYPE(type) == R_ARM_ABS32) {
>                         int index = type >> 8;
>                         unsigned long r = dynsym[index * 4 + 1];
>
>                         *fixup = *fixup + r + offset;
> +
> +                       add = 2;
> +               } else {
> +                       putc_ll('>');
> +                       puthex_ll(type);
> +                       putc_ll('\n');
> +                       /* We're doomed */
> +                       panic(NULL);
>                 }
>
>                 *dstart += offset;
> -               dstart += 2;
> +               dstart += add;
>         }
>
>         memset(dynsym, 0, (unsigned long)dynend - (unsigned long)dynsym);
> diff --git a/arch/arm/cpu/setupc_64.S b/arch/arm/cpu/setupc_64.S
> index 3515854784..88c7899205 100644
> --- a/arch/arm/cpu/setupc_64.S
> +++ b/arch/arm/cpu/setupc_64.S
> @@ -16,3 +16,61 @@ ENTRY(setup_c)
>         mov     x30, x15
>         ret
>  ENDPROC(setup_c)
> +
> +/*
> + * void relocate_to_adr(unsigned long targetadr)
> + *
> + * Copy binary to targetadr, relocate code and continue
> + * executing at new address.
> + */
> +.section .text.relocate_to_adr
> +ENTRY(relocate_to_adr)
> +                                       /* x0: target address */
> +
> +       stp     x19, x20, [sp, #-16]!
> +
> +       mov     x19, lr
> +
> +       mov     x6, x0
> +
> +       bl      get_runtime_offset
> +       mov     x5, x0
> +
> +       ldr     x0, =_text
> +       mov     x8, x0
> +
> +       add     x1, x0, x5              /* x1: from address */
> +
> +       cmp     x1, x6                  /* already at correct address? */
> +       beq     1f                      /* yes, skip copy to new address */
> +
> +       ldr     x2, =__bss_start
> +
> +       sub     x2, x2, x0              /* x2: size */
> +       mov     x0, x6                  /* x0: target */
> +
> +       /* adjust return address */
> +       sub     x19, x19, x1            /* sub address where we are actually running */
> +       add     x19, x19, x0            /* add address where we are going to run */
> +
> +       bl      memcpy                  /* copy binary */
> +
> +#ifdef CONFIG_MMU
> +       bl      arm_early_mmu_cache_flush
> +#endif
> +       mov     x0,#0
> +       ic      ivau, x0        /* flush icache */
> +
> +       ldr     x0,=1f
> +       sub     x0, x0, x8
> +       add     x0, x0, x6
> +       br      x0                      /* jump to relocated address */
> +1:
> +       bl      relocate_to_current_adr /* relocate binary */
> +
> +       mov     lr, x19
> +
> +       ldp     x19, x20, [sp], #16
> +       ret
> +
> +ENDPROC(relocate_to_adr)
> diff --git a/common/Kconfig b/common/Kconfig
> index af71d6888a..b7000c4d73 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -344,7 +344,7 @@ config KALLSYMS
>           This is useful to print a nice backtrace when an exception occurs.
>
>  config RELOCATABLE
> -       depends on PPC || (ARM && !CPU_V8)
> +       depends on PPC || ARM
>         bool "generate relocatable barebox binary"
>         help
>           A non relocatable barebox binary will run at it's compiled in
> --
> 2.16.1
>
>
> _______________________________________________
> barebox mailing list
> barebox@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/barebox

_______________________________________________
barebox mailing list
barebox@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/barebox