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 d79976918852
("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 d79976918852, 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: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220406070038.3704604-1-aik@ozlabs.ru

diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index feadee1..4454472 100644 (file)
--- a/arch/powerpc/boot/crt0.S
+++ b/arch/powerpc/boot/crt0.S
@@ -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
-       bne     11f
-       ld      r8,8(r11)       /* get RELACOUNT value in r8 */
+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
+       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 */