On 3/22/22 13:12, Michael Ellerman wrote:
Alexey Kardashevskiy <a...@ozlabs.ru> writes:
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 [2].
That's committed so you can say:
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 [1], this does not add unaligned UADDR/UADDR64 relocations
^
that should be 2?
Yes.
as in hardly possible to see those in arch-specific zImage.
I don't quite parse that. Is it true we can never see them in zImage?
Maybe it's true that we don't see them in practice.
I can force UADDR64 in zImage as I did for d79976918852 but zImage is
lot smaller and more arch-specific than vmlinux and so far only
PRINT_INDEX triggered UADDR64 in vmlinux and chances of the same thing
happening in zImage are small.
[1] https://github.com/llvm/llvm-project/commit/da0e5b885b25cf4
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=next&id=d799769188529a
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
arch/powerpc/boot/crt0.S | 43 +++++++++++++++++++++++++---------------
1 file changed, 27 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index feadee18e271..6ea3417da3b7 100644
--- 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 +76,38 @@ 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 111f
+ lwz r0,4(r12) /* get RELASZ value in r0 */
+ b 12f
+111: cmpwi r8,RELAENT
Can you use named local labels for new labels you introduce?
This could be .Lcheck_for_relaent: perhaps.
Then I'll need to rename them all/most and add more noise to the patch
which reduces chances of it being reviewed. But sure, I can rename labels.
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 */
+ divd r0,r0,r14 /* RELASZ / RELAENT */
This is in the 32-bit portion isn't it. AFAIK 32-bit CPUs don't
implement divd. I'm not sure why the toolchain allowed it. I would
expect it to trap if run on real 32-bit hardware.
Uff, my bad, "divw", right?
I am guessing it works as zImage for 64bit BigEndian is still ELF32
which runs in 64bit CPU and I did not test on real PPC32 as I'm not
quite sure how and I hoped your farm will do this for me :)
mtctr r0
2: lbz r0,4+3(r9) /* ELF32_R_INFO(reloc->r_info) */
cmpwi r0,22 /* R_PPC_RELATIVE */
- bne 3f
+ bne 22f
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
+22: add r9,r9,r14
bdnz 2b
/* Do a cache flush for our text, in case the loader didn't */
cheers
