[PATCH 30/78] ARM: aarch64: Add relocation support
Andrey Smirnov
andrew.smirnov at gmail.com
Fri Mar 16 14:51:19 PDT 2018
On Fri, Mar 16, 2018 at 5:53 AM, Sascha Hauer <s.hauer at 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 at 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
>
>
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