New: Kernel fails to boot at an early stage when built with GCC_PLUGIN_LATENT_ENTROPY=y (PowerMac G4 3,6)

https://bugzilla.kernel.org/show_bug.cgi?id=215217

Bug ID: 215217
Summary: Kernel fails to boot at an early stage when built with
GCC_PLUGIN_LATENT_ENTROPY=y (PowerMac G4 3,6)
Product: Platform Specific/Hardware
Version: 2.5
Kernel Version: 5.16-rc3
Hardware: PPC-32
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: PPC-32
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Regression: No

Created attachment 299871
--> https://bugzilla.kernel.org/attachment.cgi?id=299871&action=edit
kernel .config (5.16-rc3, PowerMac G4 DP)

Get this on my PowerMac G4 DP when I build a kernel with GCC_PLUGIN_LATENT_ENTROPY=y. The kernel gets decompressed but shortly afterwards the machine freezes, displaying in black letters on an entirely white screen:

done
found display : /pci@f0000000/ATY,AlteracParent@10/ATY,Alterac_B@1,
opening...

Same kernel config built without GCC_PLUGIN_LATENT_ENTROPY just boots fine. Happens on v5.15.5 and v5.16-rc3. I did not test other kernel versions yet.

My Talos II (Power9) on the other hand just works fine with a GCC_PLUGIN_LATENT_ENTROPY=y built kernel.

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--- Comment #1 from Christophe Leroy ([email protected]) --- POWER9 doesn't have KASAN.

Did you try G4 without KASAN ?

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--- Comment #2 from Erhard F. ([email protected]) --- Just rebuilt the kernel without KASAN but I still hit this bug.

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--- Comment #3 from Christophe Leroy ([email protected]) --- I tried your config under QEMU and it works. So I don't know how I could help.

milliseconds isn't unique.
Welcome to OpenBIOS v1.1 built on Jul 22 2021 22:33

OF stdout device is: /pci@f2000000/mac-io@c/escc@13000/ch-a@13020 Preparing to boot Linux version 5.16.0-rc3-PowerMacG4+ ([email protected]) (powerpc64-linux-gcc (GCC) 11.1.0, GNU ld (GNU Binutils) 2.36.1) #669 SMP Sun Dec 5 18:41:30 CET 2021 Detected machine type: 00000400
command line:
memory layout at init:
memory_limit : 00000000 (16 MB aligned)
alloc_bottom : 01f3e000
alloc_top : 30000000
alloc_top_hi : 80000000
rmo_top : 30000000
ram_top : 80000000
found display : /pci@f2000000/QEMU,VGA@e, opening... done
copying OF device tree...
Building dt strings...
Building dt structure...
Device tree strings 0x01f3f000 -> 0x01f3e0a4
Device tree struct 0x01f40000 -> 0x7fde7ef8
Quiescing Open Firmware ...
Booting Linux via __start() @ 0x01000000 ...
Hello World !
Total memory = 2048MB; using 4096kB for hash table
Activating Kernel Userspace Execution Prevention
Activating Kernel Userspace Access Protection
Linux version 5.16.0-rc3-PowerMacG4+ ([email protected]) (powerpc64-linux-gcc (GCC) 11.1.0, GNU ld (GNU Binutils) 2.36.1) #669 SMP Sun Dec 5 18:41:30 CET 2021
KASAN init done
ioremap() called early from pmac_feature_init+0x248/0xfe4. Use early_ioremap() instead
Found UniNorth memory controller & host bridge @ 0xf8000000 revision: 0x07 Mapped at 0xf53bf000
ioremap() called early from probe_one_macio+0x228/0x414. Use early_ioremap() instead
Found a Keylargo mac-io controller, rev: 0, mapped at 0x(ptrval) PowerMac motherboard: PowerMac G4 AGP Graphics
ioremap() called early from udbg_scc_init+0x1dc/0x380. Use early_ioremap() instead
boot stdout isn't a display !
Using PowerMac machine description
printk: bootconsole [udbg0] enabled
CPU maps initialized for 1 thread per core

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--- Comment #4 from Erhard F. ([email protected]) --- Created attachment 299935
--> https://bugzilla.kernel.org/attachment.cgi?id=299935&action=edit
kernel .config (4.18.20, PowerMac G4 DP)

Hmm, strange...

I tried to bisect but found out that this issue goes back to kernel v4.18.20 at least. This one is the earliest I am able to build with GCC_PLUGIN_LATENT_ENTROPY=y, kernels before error out with:

make: ngcc: No such file or directory
Cannot use CONFIG_GCC_PLUGINS: plugin support on gcc <= 5.1 is buggy on powerpc, please upgrade to gcc 5.2 or newer

I used gcc 9.4.0 and reduced the kernel .config a lot but it's still the same. v4.18.20 with GCC_PLUGIN_LATENT_ENTROPY=y freezes at this early boot stage, without GCC_PLUGIN_LATENT_ENTROPY booting continues.

Also GCC_PLUGIN_LATENT_ENTROPY=y makes no problem on my G5 either. So it's only the G4 which is affected. Wildly guessing this may be a 32bit PowerPC gcc specific thing?

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Michael Ellerman ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #5 from Michael Ellerman ([email protected]) --- It's likely there's some 32-bit boot code that is being instrumented in a way that causes it to crash.

We probably need to add some more uses of DISABLE_LATENT_ENTROPY_PLUGIN in arch/powerpc/kernel/Makefile.

To start with you could try adding:

  CFLAGS_setup_32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)

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--- Comment #6 from Erhard F. ([email protected]) --- Ok I cheked that out. There are already some in the Makefile:

CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)

I added CFLAGS_setup_32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) on top of that, rebuilt the kernel after a make clean. No success so far, the kernel still does not boot.

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--- Comment #7 from Erhard F. ([email protected]) --- Created attachment 299967
--> https://bugzilla.kernel.org/attachment.cgi?id=299967&action=edit
kernel .config (5.16-rc4 + CFLAGS_setup_32.o +=... , PowerMac G4 DP)

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--- Comment #8 from Christophe Leroy ([email protected]) --- early_32.o should likely also have DISABLE_LATENT_ENTROPY_PLUGIN, maybe even more important that for setup_32.o

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--- Comment #9 from Christophe Leroy ([email protected]) --- Erhard, were you able to redo the test with DISABLE_LATENT_ENTROPY_PLUGIN also disabled for early_32.o ?

If you can try with it disabled for both early_32.o and setup_32.o Then if it works, retry with it disabled only for early_32.o

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--- Comment #10 from Erhard F. ([email protected]) ---
Created attachment 300015
--> https://bugzilla.kernel.org/attachment.cgi?id=300015&action=edit
kernel zImage (5.16-rc5 + CFLAGS_setup_32.o/early_32.o +=... , PowerMac G4 DP)

Unfortunately still no success.

Relevant section in the Makefile now looks like this:
CFLAGS_early_32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_setup_32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)

I'll attach the generated zImage, maybe you can make something out of it.

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--- Comment #11 from Christophe Leroy ([email protected]) --- Ok, so that's not enough, must be something else.

I guess you are right next step should be analysis of the image.

zImage however can hardly be used for that.

Could you provide vmlinux file ?

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Erhard F. ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------

 Attachment #300015|0                           |1

is obsolete| |

--- Comment #12 from Erhard F. ([email protected]) ---
Created attachment 300027
--> https://bugzilla.kernel.org/attachment.cgi?id=300027&action=edit
kernel vmlinux.xz (5.16-rc5 + CFLAGS_setup_32.o/early_32.o +=... , PowerMac G4 DP)

Ok. I .xz-compressed it afterwards as it would be too big otherwise.

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--- Comment #13 from Christophe Leroy ([email protected]) --- arch/powerpc/lib/feature-fixups.o also need DISABLE_LATENT_ENTROPY_PLUGIN, see extract from you vmlinux below

c0c0ad20 <apply_feature_fixups>:

c0c0ad20:       94 21 ff e0     stwu    r1,-32(r1)
c0c0ad24:       3c 60 c0 db     lis     r3,-16165
c0c0ad28:       7c 08 02 a6     mflr    r0
c0c0ad2c:       38 63 55 50     addi    r3,r3,21840
c0c0ad30:       bf 41 00 08     stmw    r26,8(r1)
c0c0ad34:       7c 3f 0b 78     mr      r31,r1
c0c0ad38:       3f 60 c0 da     lis     r27,-16166         <== latent_entropy@h
c0c0ad3c:       90 01 00 24     stw     r0,36(r1)
c0c0ad40:       3f 80 c0 d4     lis     r28,-16172
c0c0ad44:       83 db 5b 50     lwz     r30,23376(r27)     <== latent_entropy@l
c0c0ad48:       4b 40 60 35     bl      c0010d7c <add_reloc_offset>

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--- Comment #14 from Erhard F. ([email protected]) --- (In reply to Christophe Leroy from comment #13)

I can confirm this works, thanks!

I need

arch/powerpc/kernel/Makefile:
CFLAGS_early_32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) arch/powerpc/lib/Makefile:
CFLAGS_feature-fixups.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)

to make it going on my G4 with GCC_PLUGIN_LATENT_ENTROPY=y. Modifying setup_32.o is not needed.

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Erhard F. ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------

             Status|NEW                         |RESOLVED
         Resolution|---                         |CODE_FIX

--- Comment #15 from Erhard F. ([email protected]) --- Fix landed in kernel 5.16.5. Thanks!

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