Commit c14d31ba authored by Alexey Kardashevskiy's avatar Alexey Kardashevskiy Committed by Michael Ellerman
Browse files

powerpc/boot: Stop using RELACOUNT 

So far the RELACOUNT tag from the ELF header was containing the exact
number of R_PPC_RELATIVE/R_PPC64_RELATIVE relocations. However the LLVM's
recent change [1] make it equal-or-less than the actual number which
makes it useless.

This replaces RELACOUNT in zImage loader with a pair of RELASZ and RELAENT.
The vmlinux relocation code is fixed in commit d7997691
("powerpc/64: Add UADDR64 relocation support").

To make it more future proof, this walks through the entire .rela.dyn
section instead of assuming that the section is sorter by a relocation
type. Unlike d7997691, this does not add unaligned UADDR/UADDR64
relocations as we are likely not to see those in practice - the zImage
is small and very arch specific so there is a smaller chance that some
generic feature (such as PRINK_INDEX) triggers unaligned relocations.

[1] https://github.com/llvm/llvm-project/commit/da0e5b885b25cf4



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/20220406070038.3704604-1-aik@ozlabs.ru
parent 3ba4289a

arch/powerpc/boot/crt0.S

+29 −16
Original line number Diff line number Diff line
@@ -8,7 +8,8 @@ 
#include "ppc_asm.h"



RELA = 7

RELACOUNT = 0x6ffffff9

RELASZ = 8

RELAENT = 9



	.data

	/* A procedure descriptor used when booting this as a COFF file.
@@ -75,34 +76,39 @@ p_base: mflr r10 /* r10 now points to runtime addr of p_base */ 
	bne	11f

	lwz	r9,4(r12)	/* get RELA pointer in r9 */

	b	12f

11:	addis	r8,r8,(-RELACOUNT)@ha

	cmpwi	r8,RELACOUNT@l

11:	cmpwi	r8,RELASZ

	bne	.Lcheck_for_relaent

	lwz	r0,4(r12)       /* get RELASZ value in r0 */

	b	12f

.Lcheck_for_relaent:

	cmpwi	r8,RELAENT

	bne	12f

	lwz	r0,4(r12)	/* get RELACOUNT value in r0 */

	lwz     r14,4(r12)      /* get RELAENT value in r14 */

12:	addi	r12,r12,8

	b	9b



	/* The relocation section contains a list of relocations.

	 * We now do the R_PPC_RELATIVE ones, which point to words

	 * which need to be initialized with addend + offset.

	 * The R_PPC_RELATIVE ones come first and there are RELACOUNT

	 * of them. */

	 * which need to be initialized with addend + offset */

10:	/* skip relocation if we don't have both */

	cmpwi	r0,0

	beq	3f

	cmpwi	r9,0

	beq	3f

	cmpwi	r14,0

	beq	3f



	add	r9,r9,r11	/* Relocate RELA pointer */

	divwu   r0,r0,r14       /* RELASZ / RELAENT */

	mtctr	r0

2:	lbz	r0,4+3(r9)	/* ELF32_R_INFO(reloc->r_info) */

	cmpwi	r0,22		/* R_PPC_RELATIVE */

	bne	3f

	bne	.Lnext

	lwz	r12,0(r9)	/* reloc->r_offset */

	lwz	r0,8(r9)	/* reloc->r_addend */

	add	r0,r0,r11

	stwx	r0,r11,r12

	addi	r9,r9,12

.Lnext:	add	r9,r9,r14

	bdnz	2b



	/* Do a cache flush for our text, in case the loader didn't */
@@ -160,32 +166,39 @@ p_base: mflr r10 /* r10 now points to runtime addr of p_base */ 
	bne	10f

	ld	r13,8(r11)       /* get RELA pointer in r13 */

	b	11f

10:	addis	r12,r12,(-RELACOUNT)@ha

	cmpdi	r12,RELACOUNT@l

10:	cmpwi   r12,RELASZ

	bne	.Lcheck_for_relaent

	lwz	r8,8(r11)	/* get RELASZ pointer in r8 */

	b	11f

.Lcheck_for_relaent:

	cmpwi	r12,RELAENT

	bne     11f

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

	lwz     r14,8(r11)      /* get RELAENT pointer in r14 */

11:	addi	r11,r11,16

	b	9b

12:

	cmpdi	r13,0            /* check we have both RELA and RELACOUNT */

	cmpdi	r13,0            /* check we have both RELA, RELASZ, RELAENT*/

	cmpdi	cr1,r8,0

	beq	3f

	beq	cr1,3f

	cmpdi	r14,0

	beq	3f



	/* Calcuate the runtime offset. */

	subf	r13,r13,r9



	/* Run through the list of relocations and process the

	 * R_PPC64_RELATIVE ones. */

	divdu   r8,r8,r14       /* RELASZ / RELAENT */

	mtctr	r8

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

	cmpdi	r0,22           /* R_PPC64_RELATIVE */

	bne	3f

	bne	.Lnext

	ld	r12,0(r9)        /* reloc->r_offset */

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

	add	r0,r0,r13

	stdx	r0,r13,r12

	addi	r9,r9,24

.Lnext:	add	r9,r9,r14

	bdnz	13b



	/* Do a cache flush for our text, in case the loader didn't */