[PATCH kernel v2] powerpc/64: Add UADDR64 relocation support
Alexey Kardashevskiy
aik at ozlabs.ru
Fri Feb 4 14:48:44 AEDT 2022
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 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 at ozlabs.ru>
---
Changes:
v2:
* replaced RELACOUNT with RELASZ/RELAENT
* removed FIXME
---
Tested via qemu gdb stub (the kernel is loaded at 0x400000).
Disasm:
c000000001a804d0 <e1>:
c000000001a804d0: b0 04 a8 01 .long 0x1a804b0
c000000001a804d0: R_PPC64_RELATIVE *ABS*-0x3ffffffffe57fb50
c000000001a804d4: 00 00 00 c0 lfs f0,0(0)
c000000001a804d8: fa 08 00 00 .long 0x8fa
c000000001a804dc <e2>:
...
c000000001a804dc: R_PPC64_UADDR64 .rodata+0x4b0
Before relocation:
>>> p *(unsigned long *) 0x1e804d0
$1 = 0xc000000001a804b0
>>> p *(unsigned long *) 0x1e804dc
$2 = 0x0
After relocation in __boot_from_prom:
>>> p *(unsigned long *) 0x1e804d0
$1 = 0x1e804b0
>>> p *(unsigned long *) 0x1e804dc
$2 = 0x1e804b0
After relocation in __after_prom_start:
>>> p *(unsigned long *) 0x1e804d0
$1 = 0xc000000001a804b0
>>> p *(unsigned long *) 0x1e804dc
$2 = 0xc000000001a804b0
>>>
---
arch/powerpc/kernel/reloc_64.S | 56 ++++++++++++++++++++----------
arch/powerpc/kernel/vmlinux.lds.S | 2 --
arch/powerpc/tools/relocs_check.sh | 7 +---
3 files changed, 39 insertions(+), 26 deletions(-)
diff --git a/arch/powerpc/kernel/reloc_64.S b/arch/powerpc/kernel/reloc_64.S
index 02d4719bf43a..f7dcc25e93d0 100644
--- 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 +27,36 @@ _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 */
cmpdi r6,0
- beq 4f /* end of list */
+ beq 5f /* 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 at l
+ b 4f
+2: cmpdi r6,RELASZ
bne 3f
- ld r8,8(r11) /* get RELACOUNT value in r8 */
-3: addi r11,r11,16
+ 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 1b
-4: cmpdi r7,0 /* check we have both RELA and RELACOUNT */
+5: cmpdi r7,0 /* check we have RELA, RELASZ, RELAENT */
cmpdi cr1,r8,0
- beq 6f
- beq cr1,6f
+ beq 10f
+ beq cr1,10f
+ cmpdi r12,0
+ beq 10f
/*
* Work out linktime address of _stext and hence the
@@ -62,23 +71,34 @@ _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) */
+5: lwa r0,8(r9) /* ELF64_R_TYPE(reloc->r_info) */
cmpdi r0,R_PPC64_RELATIVE
- bne 6f
+ bne 7f
ld r6,0(r9) /* reloc->r_offset */
ld r0,16(r9) /* reloc->r_addend */
- add r0,r0,r3
+ b 8f
+7: cmpdi r0,R_PPC64_UADDR64
+ bne 9f
+ ld r6,0(r9)
+ ld r0,16(r9)
+ lwa r14,12(r9) /* ELF64_R_SYM(reloc->r_info) */
+ 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
+8: add r0,r0,r3
stdx r0,r7,r6
- addi r9,r9,24
+9: add r9,r9,r12
bdnz 5b
-
-6: blr
+10: 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 2bcca818136a..fe22d940412f 100644
--- 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 014e00e74d2b..63792af00417 100755
--- 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
--
2.30.2
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