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:
\#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.
This adds a workaround for the number of relocations as the DT_RELACOUNT
ELF Dynamic Array Tag does not include relocations other than
R_PPC64_RELATIVE. This instead iterates over the entire .rela.dyn section.
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
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:
>>> p *(unsigned long *) 0x1e804d0
$1 = 0x1e804b0
>>> p *(unsigned long *) 0x1e804dc
$2 = 0x1e804b0
---
arch/powerpc/kernel/reloc_64.S | 47 +++++++++++++++++++++++++-----
arch/powerpc/kernel/vmlinux.lds.S | 3 +-
arch/powerpc/tools/relocs_check.sh | 6 ----
3 files changed, 41 insertions(+), 15 deletions(-)
diff --git a/arch/powerpc/kernel/reloc_64.S b/arch/powerpc/kernel/reloc_64.S
index 02d4719bf43a..a91175723d9d 100644
--- a/arch/powerpc/kernel/reloc_64.S
+++ b/arch/powerpc/kernel/reloc_64.S
@@ -10,6 +10,7 @@
RELA = 7
RELACOUNT = 0x6ffffff9
R_PPC64_RELATIVE = 22
+R_PPC64_UADDR64 = 43
/*
* r3 = desired final address of kernel
@@ -25,6 +26,8 @@ _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.
@@ -46,8 +49,8 @@ _GLOBAL(relocate)
b 1b
4: cmpdi r7,0 /* check we have both RELA and RELACOUNT */
cmpdi cr1,r8,0
- beq 6f
- beq cr1,6f
+ beq 9f
+ beq cr1,9f
/*
* Work out linktime address of _stext and hence the
@@ -60,25 +63,55 @@ _GLOBAL(relocate)
subf r10,r7,r10
subf r3,r10,r3 /* final_offset */
+ /*
+ * FIXME
+ * Here r8 is a number of relocations in .rela.dyn.
+ * When ld issues UADDR64 relocations, they end up at the end
+ * of the .rela.dyn section. However RELACOUNT does not include
+ * them so the loop below is going to finish after the last
+ * R_PPC64_RELATIVE as they normally go first.
+ * Work out the size of .rela.dyn at compile time.
+ */
+ ld r8,(p_rela_end - 0b)(r12)
+ ld r18,(p_rela - 0b)(r12)
+ sub r8,r8,r18
+ li r18,24 /* 24 == sizeof(elf64_rela) */
+ divd r8,r8,r18
+
/*
* Run through the list of relocations and process the
- * R_PPC64_RELATIVE ones.
+ * R_PPC64_RELATIVE and R_PPC64_UADDR64 ones.
*/
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
ld r6,0(r9) /* reloc->r_offset */
ld r0,16(r9) /* reloc->r_addend */
- add r0,r0,r3
+ b 7f
+
+6: cmpdi r0,R_PPC64_UADDR64
+ bne 8f
+ 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
+
+7: add r0,r0,r3
stdx r0,r7,r6
- addi r9,r9,24
+
+8: addi r9,r9,24
bdnz 5b
-6: blr
+9: blr
.balign 8
p_dyn: .8byte __dynamic_start - 0b
p_rela: .8byte __rela_dyn_start - 0b
+p_rela_end: .8byte __rela_dyn_end - 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..e9d9bda3ffaf 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) }
@@ -299,6 +297,7 @@ SECTIONS
{
__rela_dyn_start = .;
*(.rela*)
+ __rela_dyn_end = .;
}
#endif
/* .exit.data is discarded at runtime, not link time,
diff --git a/arch/powerpc/tools/relocs_check.sh
b/arch/powerpc/tools/relocs_check.sh
index 014e00e74d2b..956b9e236a60 100755
--- a/arch/powerpc/tools/relocs_check.sh
+++ b/arch/powerpc/tools/relocs_check.sh
@@ -54,9 +54,3 @@ 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
