Re: [PATCH v2 0/4] alpha: stack fixes

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hi Ivan,

On Sat, 2025-02-01 at 10:46 +0100, John Paul Adrian Glaubitz wrote:
> On Fri, 2025-01-31 at 11:41 +0100, Ivan Kokshaysky wrote:
> > This series fixes oopses on Alpha/SMP observed since kernel v6.9. [1]
> > Thanks to Magnus Lindholm for identifying that remarkably longstanding
> > bug.
> > 
> > The problem is that GCC expects 16-byte alignment of the incoming stack
> > since early 2004, as Maciej found out [2]:
> >   Having actually dug speculatively I can see that the psABI was changed in
> >  GCC 3.5 with commit e5e10fb4a350 ("re PR target/14539 (128-bit long double
> >  improperly aligned)") back in Mar 2004, when the stack pointer alignment
> >  was increased from 8 bytes to 16 bytes, and arch/alpha/kernel/entry.S has
> >  various suspicious stack pointer adjustments, starting with SP_OFF which
> >  is not a whole multiple of 16.
> > 
> > Also, as Magnus noted, "ALPHA Calling Standard" [3] required the same:
> >  D.3.1 Stack Alignment
> >   This standard requires that stacks be octaword aligned at the time a
> >   new procedure is invoked.
> > 
> > However:
> > - the "normal" kernel stack is always misaligned by 8 bytes, thanks to
> >   the odd number of 64-bit words in 'struct pt_regs', which is the very
> >   first thing pushed onto the kernel thread stack;
> > - syscall, fault, interrupt etc. handlers may, or may not, receive aligned
> >   stack depending on numerous factors.
> > 
> > Somehow we got away with it until recently, when we ended up with
> > a stack corruption in kernel/smp.c:smp_call_function_single() due to
> > its use of 32-byte aligned local data and the compiler doing clever
> > things allocating it on the stack.
> > 
> > Patches 1-2 are preparatory; 3 - the main fix; 4 - fixes remaining
> > special cases.
> > 
> > Ivan.
> > 
> > [1] https://lore.kernel.org/rcu/CA+=Fv5R9NG+1SHU9QV9hjmavycHKpnNyerQ=Ei90G98ukRcRJA@mail.gmail.com/#r
> > [2] https://lore.kernel.org/rcu/alpine.DEB.2.21.2501130248010.18889@angie.orcam.me.uk/
> > [3] https://bitsavers.org/pdf/dec/alpha/Alpha_Calling_Standard_Rev_2.0_19900427.pdf
> > ---
> > Changes in v2:
> > - patch #1: provide empty 'struct pt_regs' to fix compile failure in libbpf,
> >   reported by John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>;
> >   update comment and commit message accordingly;
> > - cc'ed <stable@vger.kernel.org> as older kernels ought to be fixed as well.
> > ---
> > Ivan Kokshaysky (4):
> >   alpha/uapi: do not expose kernel-only stack frame structures
> >   alpha: replace hardcoded stack offsets with autogenerated ones
> >   alpha: make stack 16-byte aligned (most cases)
> >   alpha: align stack for page fault and user unaligned trap handlers
> > 
> >  arch/alpha/include/asm/ptrace.h      | 64 ++++++++++++++++++++++++++-
> >  arch/alpha/include/uapi/asm/ptrace.h | 65 ++--------------------------
> >  arch/alpha/kernel/asm-offsets.c      |  4 ++
> >  arch/alpha/kernel/entry.S            | 24 +++++-----
> >  arch/alpha/kernel/traps.c            |  2 +-
> >  arch/alpha/mm/fault.c                |  4 +-
> >  6 files changed, 83 insertions(+), 80 deletions(-)
> 
> Thanks, I'm testing the v2 series of the patches now.

I have applied the series, but I am seeing gcc crashes from time to time:

/build/reproducible-path/palapeli-24.12.1/obj-alpha-linux-gnu/mime/palathumbcreator_autogen/include/thumbnail-creator.moc: In function ‘QObject* qt_plugin_instance()’:
/build/reproducible-path/palapeli-24.12.1/obj-alpha-linux-gnu/mime/palathumbcreator_autogen/include/thumbnail-creator.moc:328:1: error: unrecognizable insn:
  328 | QT_MOC_EXPORT_PLUGIN_V2(palathumbcreator_factory, palathumbcreator_factory, qt_pluginMetaDataV2_palathumbcreator_factory)
      | ^~~~~~~~~~~~~~~~~~~~~~~
(jump_insn 331 295 332 3 (set (pc)
        (address:DI 1)) -1
     (nil)
 -> 40)
during RTL pass: sched1
/build/reproducible-path/palapeli-24.12.1/obj-alpha-linux-gnu/mime/palathumbcreator_autogen/include/thumbnail-creator.moc:328:1: internal compiler error: in extract_insn, at recog.cc:2812
0x12195fc8b internal_error(char const*, ...)
	???:0
0x1201f37b7 fancy_abort(char const*, int, char const*)
	???:0
0x1201f0a6f _fatal_insn(char const*, rtx_def const*, char const*, int, char const*)
	???:0
0x1201f0ab7 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
	???:0
0x120b5ff97 extract_insn(rtx_insn*)
	???:0
0x12179d003 deps_analyze_insn(deps_desc*, rtx_insn*)
	???:0
0x12179d98f sched_analyze(deps_desc*, rtx_insn*, rtx_insn*)
	???:0
0x120bb0517 sched_rgn_compute_dependencies(int)
	???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-14/README.Bugs> for instructions.
The bug is not reproducible, so it is likely a hardware or OS problem.

See: https://buildd.debian.org/status/fetch.php?pkg=palapeli&arch=alpha&ver=4%3A24.12.1-1&stamp=1738215920&raw=0

But this might be related to CONFIG_COMPACTION as Michael Cree already mentioned
as this option is enabled in Debian by default on all architectures except for
m68k.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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