* [PATCH kernel v2] powerpc/boot: Stop using RELACOUNT
@ 2022-04-06 4:01 Alexey Kardashevskiy
2022-04-06 4:58 ` Gabriel Paubert
0 siblings, 1 reply; 3+ messages in thread
From: Alexey Kardashevskiy @ 2022-04-06 4:01 UTC (permalink / raw)
To: linuxppc-dev
Cc: Alexey Kardashevskiy, llvm, Nick Desaulniers, Nathan Chancellor
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>
---
Changes:
v2:
* s/divd/divwu/ for ppc32
* updated the commit log
* named all new labels instead of numbering them
(s/101f/.Lcheck_for_relaent/ and so on)
---
arch/powerpc/boot/crt0.S | 45 ++++++++++++++++++++++++++--------------
1 file changed, 29 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
index feadee18e271..e9306d862f8d 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 +76,39 @@ 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. */
+ divd 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 */
--
2.30.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH kernel v2] powerpc/boot: Stop using RELACOUNT
2022-04-06 4:01 [PATCH kernel v2] powerpc/boot: Stop using RELACOUNT Alexey Kardashevskiy
@ 2022-04-06 4:58 ` Gabriel Paubert
2022-04-06 6:55 ` Alexey Kardashevskiy
0 siblings, 1 reply; 3+ messages in thread
From: Gabriel Paubert @ 2022-04-06 4:58 UTC (permalink / raw)
To: Alexey Kardashevskiy
Cc: Nathan Chancellor, Nick Desaulniers, llvm, linuxppc-dev
On Wed, Apr 06, 2022 at 02:01:48PM +1000, Alexey Kardashevskiy wrote:
> 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>
> ---
> Changes:
> v2:
> * s/divd/divwu/ for ppc32
> * updated the commit log
> * named all new labels instead of numbering them
> (s/101f/.Lcheck_for_relaent/ and so on)
> ---
> arch/powerpc/boot/crt0.S | 45 ++++++++++++++++++++++++++--------------
> 1 file changed, 29 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
> index feadee18e271..e9306d862f8d 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 +76,39 @@ 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. */
> + divd r8,r8,r14 /* RELASZ / RELAENT */
While you are at it, this one should also be divdu.
I really wished IBM had used explicit signed/unsigned indication in the
mnemonics (divds, divdu, divws, divwu) instead. Fortunately very little
assemby code uses these instructions nowadays.
> 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 */
> --
> 2.30.2
Cheers,
Gabriel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH kernel v2] powerpc/boot: Stop using RELACOUNT
2022-04-06 4:58 ` Gabriel Paubert
@ 2022-04-06 6:55 ` Alexey Kardashevskiy
0 siblings, 0 replies; 3+ messages in thread
From: Alexey Kardashevskiy @ 2022-04-06 6:55 UTC (permalink / raw)
To: Gabriel Paubert; +Cc: Nathan Chancellor, Nick Desaulniers, llvm, linuxppc-dev
On 4/6/22 14:58, Gabriel Paubert wrote:
> On Wed, Apr 06, 2022 at 02:01:48PM +1000, Alexey Kardashevskiy wrote:
>> 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>
>> ---
>> Changes:
>> v2:
>> * s/divd/divwu/ for ppc32
>> * updated the commit log
>> * named all new labels instead of numbering them
>> (s/101f/.Lcheck_for_relaent/ and so on)
>> ---
>> arch/powerpc/boot/crt0.S | 45 ++++++++++++++++++++++++++--------------
>> 1 file changed, 29 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S
>> index feadee18e271..e9306d862f8d 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 +76,39 @@ 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. */
>> + divd r8,r8,r14 /* RELASZ / RELAENT */
>
> While you are at it, this one should also be divdu.
>
> I really wished IBM had used explicit signed/unsigned indication in the
> mnemonics (divds, divdu, divws, divwu) instead. Fortunately very little
> assemby code uses these instructions nowadays.
Fair enough, v3 is coming. Thanks,
>
>
>> 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 */
>> --
>> 2.30.2
>
> Cheers,
> Gabriel
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-04-06 4:01 [PATCH kernel v2] powerpc/boot: Stop using RELACOUNT Alexey Kardashevskiy
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