* Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
@ 2019-04-29 10:38 John Paul Adrian Glaubitz
2019-04-29 11:34 ` John Paul Adrian Glaubitz
0 siblings, 1 reply; 6+ messages in thread
From: John Paul Adrian Glaubitz @ 2019-04-29 10:38 UTC (permalink / raw)
To: Tony Luck
Cc: Sergei Trofimovich, Frank Scheiner, Fenghua Yu, linux-ia64, linux-kernel
Hello!
Is there a chance that Sergey's patch from [1] could get applied upstream?
Currently, the kernel in Debian doesn't boot on the RX2800 and crashes very
early directly after the bootloader. I can also confirm that both strace
and gdb currently don't build on Debian/ia64 due to this particular bug.
Thanks,
Adrian
> [1] https://lkml.org/lkml/2018/2/2/914
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
@ 2018-02-02 22:12 Sergei Trofimovich
2018-02-02 22:22 ` Luck, Tony
0 siblings, 1 reply; 6+ messages in thread
From: Sergei Trofimovich @ 2018-02-02 22:12 UTC (permalink / raw)
To: Tony Luck, Fenghua Yu, linux-ia64, linux-kernel; +Cc: Sergei Trofimovich
The strace breakage looks like that:
./strace: get_regs: get_regs_error: Input/output error
It happens because ia64 needs to load unwind tables
to read certain registers. Unwind tables fail to load
due to GCC quirk on the following code:
extern char __end_unwind[];
const struct unw_table_entry *end = (struct unw_table_entry *)table_end;
table->end = segment_base + end[-1].end_offset;
GCC does not generate correct code for this single memory
reference after constant propagation (see https://gcc.gnu.org/PR84184).
Two triggers are required for bad code generation:
- '__end_unwind' has alignment lower (char), than
'struct unw_table_entry' (8).
- symbol offset is negative.
This commit workarounds it by fixing alignment of '__end_unwind'.
While at it use hidden symbols to generate shorter gp-relative
relocations.
CC: Tony Luck <tony.luck@intel.com>
CC: Fenghua Yu <fenghua.yu@intel.com>
CC: linux-ia64@vger.kernel.org
CC: linux-kernel@vger.kernel.org
Bug: https://github.com/strace/strace/issues/33
Bug: https://gcc.gnu.org/PR84184
Reported-by: Émeric Maschino <emeric.maschino@gmail.com>
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---
arch/ia64/include/asm/sections.h | 1 -
arch/ia64/kernel/unwind.c | 15 ++++++++++++++-
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
index f3481408594e..0fc4f1757a44 100644
--- a/arch/ia64/include/asm/sections.h
+++ b/arch/ia64/include/asm/sections.h
@@ -24,7 +24,6 @@ extern char __start_gate_mckinley_e9_patchlist[], __end_gate_mckinley_e9_patchli
extern char __start_gate_vtop_patchlist[], __end_gate_vtop_patchlist[];
extern char __start_gate_fsyscall_patchlist[], __end_gate_fsyscall_patchlist[];
extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_bubble_down_patchlist[];
-extern char __start_unwind[], __end_unwind[];
extern char __start_ivt_text[], __end_ivt_text[];
#undef dereference_function_descriptor
diff --git a/arch/ia64/kernel/unwind.c b/arch/ia64/kernel/unwind.c
index e04efa088902..025ba6700790 100644
--- a/arch/ia64/kernel/unwind.c
+++ b/arch/ia64/kernel/unwind.c
@@ -2243,7 +2243,20 @@ __initcall(create_gate_table);
void __init
unw_init (void)
{
- extern char __gp[];
+ #define __ia64_hidden __attribute__((visibility("hidden")))
+ /*
+ * We use hidden symbols to generate more efficient code using
+ * gp-relative addressing.
+ */
+ extern char __gp[] __ia64_hidden;
+ /*
+ * Unwind tables need to have proper alignment as init_unwind_table()
+ * uses negative offsets against '__end_unwind'.
+ * See https://gcc.gnu.org/PR84184
+ */
+ extern const struct unw_table_entry __start_unwind[] __ia64_hidden;
+ extern const struct unw_table_entry __end_unwind[] __ia64_hidden;
+ #undef __ia64_hidden
extern void unw_hash_index_t_is_too_narrow (void);
long i, off;
--
2.16.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
2018-02-02 22:12 Sergei Trofimovich
@ 2018-02-02 22:22 ` Luck, Tony
2018-02-02 23:02 ` Sergei Trofimovich
0 siblings, 1 reply; 6+ messages in thread
From: Luck, Tony @ 2018-02-02 22:22 UTC (permalink / raw)
To: Sergei Trofimovich; +Cc: Fenghua Yu, linux-ia64, linux-kernel
On Fri, Feb 02, 2018 at 10:12:24PM +0000, Sergei Trofimovich wrote:
> The strace breakage looks like that:
> ./strace: get_regs: get_regs_error: Input/output error
>
> It happens because ia64 needs to load unwind tables
> to read certain registers. Unwind tables fail to load
> due to GCC quirk on the following code:
>
> extern char __end_unwind[];
> const struct unw_table_entry *end = (struct unw_table_entry *)table_end;
> table->end = segment_base + end[-1].end_offset;
>
> GCC does not generate correct code for this single memory
> reference after constant propagation (see https://gcc.gnu.org/PR84184).
I'm not seeing this ... probably because I build with
a pre-historic 4.3.4 version of gcc.
Do you know which version(s) are affected? I'm not looking
for an exhaustive list, just the one on which you found this
would be good.
-Tony
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
2018-02-02 22:22 ` Luck, Tony
@ 2018-02-02 23:02 ` Sergei Trofimovich
2018-02-11 18:51 ` Sergei Trofimovich
0 siblings, 1 reply; 6+ messages in thread
From: Sergei Trofimovich @ 2018-02-02 23:02 UTC (permalink / raw)
To: Luck, Tony; +Cc: Fenghua Yu, linux-ia64, linux-kernel
On Fri, 2 Feb 2018 14:22:32 -0800
"Luck, Tony" <tony.luck@intel.com> wrote:
> On Fri, Feb 02, 2018 at 10:12:24PM +0000, Sergei Trofimovich wrote:
> > The strace breakage looks like that:
> > ./strace: get_regs: get_regs_error: Input/output error
> >
> > It happens because ia64 needs to load unwind tables
> > to read certain registers. Unwind tables fail to load
> > due to GCC quirk on the following code:
> >
> > extern char __end_unwind[];
> > const struct unw_table_entry *end = (struct unw_table_entry *)table_end;
> > table->end = segment_base + end[-1].end_offset;
> >
> > GCC does not generate correct code for this single memory
> > reference after constant propagation (see https://gcc.gnu.org/PR84184).
>
> I'm not seeing this ... probably because I build with
> a pre-historic 4.3.4 version of gcc.
>
> Do you know which version(s) are affected? I'm not looking
> for an exhaustive list, just the one on which you found this
> would be good.
>
> -Tony
Original bug https://bugs.gentoo.org/518130 claims regression appeared
around gcc-4.5. Locally am seeing the problem with gcc-6.4.0, gcc-7.2.0 and
gcc-8 (HEAD).
--
Sergei
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
2018-02-02 23:02 ` Sergei Trofimovich
@ 2018-02-11 18:51 ` Sergei Trofimovich
0 siblings, 0 replies; 6+ messages in thread
From: Sergei Trofimovich @ 2018-02-11 18:51 UTC (permalink / raw)
To: Luck, Tony; +Cc: Fenghua Yu, linux-ia64, linux-kernel, stanton_arch
On Fri, 2 Feb 2018 23:02:20 +0000
Sergei Trofimovich <slyfox@gentoo.org> wrote:
> On Fri, 2 Feb 2018 14:22:32 -0800
> "Luck, Tony" <tony.luck@intel.com> wrote:
>
> > On Fri, Feb 02, 2018 at 10:12:24PM +0000, Sergei Trofimovich wrote:
> > > The strace breakage looks like that:
> > > ./strace: get_regs: get_regs_error: Input/output error
> > >
> > > It happens because ia64 needs to load unwind tables
> > > to read certain registers. Unwind tables fail to load
> > > due to GCC quirk on the following code:
> > >
> > > extern char __end_unwind[];
> > > const struct unw_table_entry *end = (struct unw_table_entry *)table_end;
> > > table->end = segment_base + end[-1].end_offset;
> > >
> > > GCC does not generate correct code for this single memory
> > > reference after constant propagation (see https://gcc.gnu.org/PR84184).
> >
> > I'm not seeing this ... probably because I build with
> > a pre-historic 4.3.4 version of gcc.
> >
> > Do you know which version(s) are affected? I'm not looking
> > for an exhaustive list, just the one on which you found this
> > would be good.
> >
> > -Tony
>
> Original bug https://bugs.gentoo.org/518130 claims regression appeared
> around gcc-4.5. Locally am seeing the problem with gcc-6.4.0, gcc-7.2.0 and
> gcc-8 (HEAD).
Another report on the positive patch effect:
rx2600 boots successfully with this patch (did not without, my guess is due to
early access fault at bad address): https://bugs.gentoo.org/579278#c13
Tested-by: stanton_arch@mail.com
--
Sergei
^ permalink raw reply [flat|nested] 6+ messages in thread
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2019-04-29 10:38 [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb) John Paul Adrian Glaubitz
2019-04-29 11:34 ` John Paul Adrian Glaubitz
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2018-02-02 22:12 Sergei Trofimovich
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