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: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220309061822.168173-1-aik@ozlabs.ru

diff --git a/arch/powerpc/kernel/reloc_64.S b/arch/powerpc/kernel/reloc_64.S
index 02d4719..232e454 100644 (file)
--- a/arch/powerpc/kernel/reloc_64.S
+++ b/arch/powerpc/kernel/reloc_64.S
@@ -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
 

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 2bcca81..fe22d94 100644 (file)
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -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) }

diff --git a/arch/powerpc/tools/relocs_check.sh b/arch/powerpc/tools/relocs_check.sh
index 014e00e..63792af 100755 (executable)
--- a/arch/powerpc/tools/relocs_check.sh
+++ b/arch/powerpc/tools/relocs_check.sh
@@ -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