Re: PPC32: Boot regression on Nintendo Wii, after create_branch rework in 5.8
Hi,
Le 28/04/2021 à 20:14, Jonathan Neuschäfer a écrit :
Hi,
On Wed, Apr 28, 2021 at 11:33:24AM +1000, Jordan Niethe wrote:
On Mon, Apr 26, 2021 at 1:40 AM Jonathan Neuschäfer
wrote:
Hi,
I recently booted my Wii again, and I noticed a regression at boot time.
Output stops after the "Finalizing device tree... flat tree at 0xXX"
message. I bisected it to this commit in the 5.8 development cycle:
commit 7c95d8893fb55869882c9f68f4c94840dc43f18f
Author: Jordan Niethe
Date: Wed May 6 13:40:25 2020 +1000
powerpc: Change calling convention for create_branch() et. al.
[...]
Do you have any hints on how to debug and/or fix this issue?
Thanks for bisecting and reporting.
The "Finalizing device tree... flat tree at 0xXX" message comes
from the bootwrapper so if that is the last output it must be crashing
pretty early.
Commit 7c95d8893fb5 ("powerpc: Change calling convention for
create_branch() et. al.") made a change to machine_init() in
setup_32.c which seems like it might be a likely culprit for causing
early crashing.
The branch that is created and patched is just for optimization, so to
see if that is in fact the problem it might be worth trying to boot
with a patch like below
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -87,9 +87,6 @@ notrace void __init machine_init(u64 dt_ptr)
patch_instruction_site(__memcpy_nocache, ppc_inst(PPC_INST_NOP));
- create_cond_branch(, addr, branch_target(addr), 0x82);
- patch_instruction(addr, insn); /* replace b by bne cr0 */
-
/* Do some early initialization based on the flat device tree */
early_init_devtree(__va(dt_ptr));
This brings no improvement, unfortunately. The output is still:
top of MEM2 @ 13F0
zImage starting: loaded at 0x00b0 (sp: 0x01145f90)
Allocating 0xae3970 bytes for kernel...
Decompressing (0x <- 0x00b11000:0x01143576)...
Done! Decompressed 0xa65fdc bytes
Linux/PowerPC load: root=/dev/mmcblk0p2 rootwait console=usbgecko1
Finalizing device tree... flat tree at 0x11467a0
I'll probably dig deeper next weekend.
I think the problem is when calling apply_feature_fixups() from early_init().
At that time, code is not relocated yet and 'current' is not set up yet.
You probably have CONFIG_STACKPROTECTOR=y
Before this patch, do_feature_fixups() was a simple fonction that was not using the stack for
storing data. But that patch changed it because it addresses the 'instr' by reference so it can't go
in a general reg anymore, it goes into the stack.
So GCC sets up a stack guard:
:
0: 7c 04 28 40 cmplw r4,r5
4: 94 21 ff b0 stwur1,-80(r1)
8: 81 22 02 28 lwz r9,552(r2) <= r2 is not set up yet
c: 91 21 00 1c stw r9,28(r1)
...
180: 81 21 00 1c lwz r9,28(r1)
184: 81 42 02 28 lwz r10,552(r2)
188: 7d 29 52 79 xor.r9,r9,r10
18c: 39 40 00 00 li r10,0
190: 40 82 00 84 bne 214
194: 38 21 00 50 addir1,r1,80
198: 4e 80 00 20 blr
...
214: 7c 08 02 a6 mflrr0
218: 90 01 00 54 stw r0,84(r1)
21c: 92 e1 00 2c stw r23,44(r1)
220: 93 01 00 30 stw r24,48(r1)
224: 93 21 00 34 stw r25,52(r1)
228: 93 41 00 38 stw r26,56(r1)
22c: 93 61 00 3c stw r27,60(r1)
230: 93 81 00 40 stw r28,64(r1)
234: 93 a1 00 44 stw r29,68(r1)
238: 93 c1 00 48 stw r30,72(r1)
23c: 93 e1 00 4c stw r31,76(r1)
240: 48 00 00 01 bl 240
240: R_PPC_REL24__stack_chk_fail
So all feature fixup and code patching stuff it uses needs to be protected
against the stack protector.
By the way, I also see some printk in do_feature_fixups(). That won't work either because of the
relocation, the string won't be found. But that's not the problem you have at the moment.
Christophe
Re: PPC32: Boot regression on Nintendo Wii, after create_branch rework in 5.8
Hi,
On Wed, Apr 28, 2021 at 11:33:24AM +1000, Jordan Niethe wrote:
> On Mon, Apr 26, 2021 at 1:40 AM Jonathan Neuschäfer
> wrote:
> >
> > Hi,
> >
> > I recently booted my Wii again, and I noticed a regression at boot time.
> > Output stops after the "Finalizing device tree... flat tree at 0xXX"
> > message. I bisected it to this commit in the 5.8 development cycle:
> >
> > commit 7c95d8893fb55869882c9f68f4c94840dc43f18f
> > Author: Jordan Niethe
> > Date: Wed May 6 13:40:25 2020 +1000
> >
> > powerpc: Change calling convention for create_branch() et. al.
[...]
> > Do you have any hints on how to debug and/or fix this issue?
> Thanks for bisecting and reporting.
> The "Finalizing device tree... flat tree at 0xXX" message comes
> from the bootwrapper so if that is the last output it must be crashing
> pretty early.
> Commit 7c95d8893fb5 ("powerpc: Change calling convention for
> create_branch() et. al.") made a change to machine_init() in
> setup_32.c which seems like it might be a likely culprit for causing
> early crashing.
> The branch that is created and patched is just for optimization, so to
> see if that is in fact the problem it might be worth trying to boot
> with a patch like below
>
> diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
> --- a/arch/powerpc/kernel/setup_32.c
> +++ b/arch/powerpc/kernel/setup_32.c
> @@ -87,9 +87,6 @@ notrace void __init machine_init(u64 dt_ptr)
>
> patch_instruction_site(__memcpy_nocache,
> ppc_inst(PPC_INST_NOP));
>
> - create_cond_branch(, addr, branch_target(addr), 0x82);
> - patch_instruction(addr, insn); /* replace b by bne cr0 */
> -
> /* Do some early initialization based on the flat device tree */
> early_init_devtree(__va(dt_ptr));
This brings no improvement, unfortunately. The output is still:
top of MEM2 @ 13F0
zImage starting: loaded at 0x00b0 (sp: 0x01145f90)
Allocating 0xae3970 bytes for kernel...
Decompressing (0x <- 0x00b11000:0x01143576)...
Done! Decompressed 0xa65fdc bytes
Linux/PowerPC load: root=/dev/mmcblk0p2 rootwait console=usbgecko1
Finalizing device tree... flat tree at 0x11467a0
I'll probably dig deeper next weekend.
Jonathan
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Re: PPC32: Boot regression on Nintendo Wii, after create_branch rework in 5.8
On Mon, Apr 26, 2021 at 1:40 AM Jonathan Neuschäfer
wrote:
>
> Hi,
>
> I recently booted my Wii again, and I noticed a regression at boot time.
> Output stops after the "Finalizing device tree... flat tree at 0xXX"
> message. I bisected it to this commit in the 5.8 development cycle:
>
> commit 7c95d8893fb55869882c9f68f4c94840dc43f18f
> Author: Jordan Niethe
> Date: Wed May 6 13:40:25 2020 +1000
>
> powerpc: Change calling convention for create_branch() et. al.
>
> create_branch(), create_cond_branch() and translate_branch() return the
> instruction that they create, or return 0 to signal an error. Separate
> these concerns in preparation for an instruction type that is not just
> an unsigned int. Fill the created instruction to a pointer passed as
> the first parameter to the function and use a non-zero return value to
> signify an error.
>
> Signed-off-by: Jordan Niethe
> Signed-off-by: Michael Ellerman
> Reviewed-by: Alistair Popple
> Link: https://lore.kernel.org/r/20200506034050.24806-6-jniet...@gmail.com
>
> arch/powerpc/include/asm/code-patching.h | 12 +--
> arch/powerpc/kernel/optprobes.c | 24 +++---
> arch/powerpc/kernel/setup_32.c | 4 +-
> arch/powerpc/kernel/trace/ftrace.c | 24 +++---
> arch/powerpc/lib/code-patching.c | 134
> ++-
> arch/powerpc/lib/feature-fixups.c| 5 +-
> 6 files changed, 119 insertions(+), 84 deletions(-)
>
>
> Do you have any hints on how to debug and/or fix this issue?
Thanks for bisecting and reporting.
The "Finalizing device tree... flat tree at 0xXX" message comes
from the bootwrapper so if that is the last output it must be crashing
pretty early.
Commit 7c95d8893fb5 ("powerpc: Change calling convention for
create_branch() et. al.") made a change to machine_init() in
setup_32.c which seems like it might be a likely culprit for causing
early crashing.
The branch that is created and patched is just for optimization, so to
see if that is in fact the problem it might be worth trying to boot
with a patch like below
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -87,9 +87,6 @@ notrace void __init machine_init(u64 dt_ptr)
patch_instruction_site(__memcpy_nocache, ppc_inst(PPC_INST_NOP));
- create_cond_branch(, addr, branch_target(addr), 0x82);
- patch_instruction(addr, insn); /* replace b by bne cr0 */
-
/* Do some early initialization based on the flat device tree */
early_init_devtree(__va(dt_ptr));
>
>
> Best regards,
> Jonathan Neuschäfer
