Commit d7997691 authored by Alexey Kardashevskiy's avatar Alexey Kardashevskiy Committed by Michael Ellerman
Browse files

powerpc/64: Add UADDR64 relocation support 



When ld detects unaligned relocations, it emits R_PPC64_UADDR64
relocations instead of R_PPC64_RELATIVE. Currently R_PPC64_UADDR64 are
detected by arch/powerpc/tools/relocs_check.sh and expected not to work.
Below is a simple chunk to trigger this behaviour (this disables
optimization for the demonstration purposes only, this also happens with
-O1/-O2 when CONFIG_PRINTK_INDEX=y, for example):

  \#pragma GCC push_options
  \#pragma GCC optimize ("O0")
  struct entry {
          const char *file;
          int line;
  } __attribute__((packed));
  static const struct entry e1 = { .file = __FILE__, .line = __LINE__ };
  static const struct entry e2 = { .file = __FILE__, .line = __LINE__ };
  ...
  prom_printf("e1=%s %lx %lx\n", e1.file, (unsigned long) e1.file, mfmsr());
  prom_printf("e2=%s %lx\n", e2.file, (unsigned long) e2.file);
  \#pragma GCC pop_options

This adds support for UADDR64 for 64bit. This reuses __dynamic_symtab
from the 32bit code which supports more relocation types already.

Because RELACOUNT includes only R_PPC64_RELATIVE, this replaces it with
RELASZ which is the size of all relocation records.

Signed-off-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220309061822.168173-1-aik@ozlabs.ru
parent 3fd46e55

arch/powerpc/kernel/reloc_64.S

+47 −20
Original line number Diff line number Diff line
@@ -8,8 +8,10 @@ 
#include <asm/ppc_asm.h>



RELA = 7

RELACOUNT = 0x6ffffff9

RELASZ = 8

RELAENT = 9

R_PPC64_RELATIVE = 22

R_PPC64_UADDR64 = 43



/*

 * r3 = desired final address of kernel
@@ -25,29 +27,38 @@ _GLOBAL(relocate) 
	add	r9,r9,r12	/* r9 has runtime addr of .rela.dyn section */

	ld	r10,(p_st - 0b)(r12)

	add	r10,r10,r12	/* r10 has runtime addr of _stext */

	ld	r13,(p_sym - 0b)(r12)

	add	r13,r13,r12	/* r13 has runtime addr of .dynsym */



	/*

	 * Scan the dynamic section for the RELA and RELACOUNT entries.

	 * Scan the dynamic section for the RELA, RELASZ and RELAENT entries.

	 */

	li	r7,0

	li	r8,0

1:	ld	r6,0(r11)	/* get tag */

.Ltags:

	ld	r6,0(r11)	/* get tag */

	cmpdi	r6,0

	beq	4f		/* end of list */

	beq	.Lend_of_list		/* end of list */

	cmpdi	r6,RELA

	bne	2f

	ld	r7,8(r11)	/* get RELA pointer in r7 */

	b	3f

2:	addis	r6,r6,(-RELACOUNT)@ha

	cmpdi	r6,RELACOUNT@l

	b	4f

2:	cmpdi	r6,RELASZ

	bne	3f

	ld	r8,8(r11)	/* get RELACOUNT value in r8 */

3:	addi	r11,r11,16

	b	1b

4:	cmpdi	r7,0		/* check we have both RELA and RELACOUNT */

	ld	r8,8(r11)	/* get RELASZ value in r8 */

	b	4f

3:	cmpdi	r6,RELAENT

	bne	4f

	ld	r12,8(r11)	/* get RELAENT value in r12 */

4:	addi	r11,r11,16

	b	.Ltags

.Lend_of_list:

	cmpdi	r7,0		/* check we have RELA, RELASZ, RELAENT */

	cmpdi	cr1,r8,0

	beq	6f

	beq	cr1,6f

	beq	.Lout

	beq	cr1,.Lout

	cmpdi	r12,0

	beq	.Lout



	/*

	 * Work out linktime address of _stext and hence the
@@ -62,23 +73,39 @@ _GLOBAL(relocate) 


	/*

	 * Run through the list of relocations and process the

	 * R_PPC64_RELATIVE ones.

	 * R_PPC64_RELATIVE and R_PPC64_UADDR64 ones.

	 */

	divd	r8,r8,r12	/* RELASZ / RELAENT */

	mtctr	r8

5:	ld	r0,8(9)		/* ELF64_R_TYPE(reloc->r_info) */

.Lrels:	ld	r0,8(r9)		/* ELF64_R_TYPE(reloc->r_info) */

	cmpdi	r0,R_PPC64_RELATIVE

	bne	6f

	bne	.Luaddr64

	ld	r6,0(r9)	/* reloc->r_offset */

	ld	r0,16(r9)	/* reloc->r_addend */

	b	.Lstore

.Luaddr64:

	srdi	r14,r0,32	/* ELF64_R_SYM(reloc->r_info) */

	clrldi	r0,r0,32

	cmpdi	r0,R_PPC64_UADDR64

	bne	.Lnext

	ld	r6,0(r9)

	ld	r0,16(r9)

	mulli	r14,r14,24	/* 24 == sizeof(elf64_sym) */

	add	r14,r14,r13	/* elf64_sym[ELF64_R_SYM] */

	ld	r14,8(r14)

	add	r0,r0,r14

.Lstore:

	add	r0,r0,r3

	stdx	r0,r7,r6

	addi	r9,r9,24

	bdnz	5b



6:	blr

.Lnext:

	add	r9,r9,r12

	bdnz	.Lrels

.Lout:

	blr



.balign 8

p_dyn:	.8byte	__dynamic_start - 0b

p_rela:	.8byte	__rela_dyn_start - 0b

p_sym:		.8byte __dynamic_symtab - 0b

p_st:	.8byte	_stext - 0b

arch/powerpc/kernel/vmlinux.lds.S

+0 −2
Original line number Diff line number Diff line
@@ -281,9 +281,7 @@ SECTIONS 
	. = ALIGN(8);

	.dynsym : AT(ADDR(.dynsym) - LOAD_OFFSET)

	{

#ifdef CONFIG_PPC32

		__dynamic_symtab = .;

#endif

		*(.dynsym)

	}

	.dynstr : AT(ADDR(.dynstr) - LOAD_OFFSET) { *(.dynstr) }

arch/powerpc/tools/relocs_check.sh

+1 −6
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ $objdump -R "$vmlinux" | 
	#	R_PPC_NONE

	grep -F -w -v 'R_PPC64_RELATIVE

R_PPC64_NONE

R_PPC64_UADDR64

R_PPC_ADDR16_LO

R_PPC_ADDR16_HI

R_PPC_ADDR16_HA
@@ -54,9 +55,3 @@ fi 
num_bad=$(echo "$bad_relocs" | wc -l)

echo "WARNING: $num_bad bad relocations"

echo "$bad_relocs"
 


# If we see this type of relocation it's an idication that

# we /may/ be using an old version of binutils.

if echo "$bad_relocs" | grep -q -F -w R_PPC64_UADDR64; then

	echo "WARNING: You need at least binutils >= 2.19 to build a CONFIG_RELOCATABLE kernel"

fi