linux-kernel - Re: [PATCH 0/5] [RFC] printk/ia64/ppc64/parisc64: let's deprecate %pF/%pf printk specifiers

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Date:   Tue, 19 Sep 2017 22:03:57 +0200
From:   Helge Deller <deller@....de>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "James E . J . Bottomley" <jejb@...isc-linux.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] [RFC] printk/ia64/ppc64/parisc64: let's deprecate
 %pF/%pf printk specifiers

* Helge Deller <deller@....de>:
> On 19.09.2017 04:05, Sergey Senozhatsky wrote:
> >On (09/18/17 20:39), Helge Deller wrote:
> >>I did tried your testcases [on parisc] too.
> ...
> >>and here is "modprobe zram":
> >>  printk#7 __UNIQUE_ID_vermagic8+0xb9a4/0xbd04 [zram]
> >>  printk#8 __UNIQUE_ID_vermagic8+0xb9a4/0xbd04 [zram]
> >>  printk#9 do_one_initcall+0x194/0x290
> >>  printk#10 do_one_initcall+0x194/0x290
> >>  printk#11 do_one_initcall+0x194/0x290
> >>  printk#12 do_one_initcall+0x194/0x290
> >>  printk#13 zram_init+0x22c/0x2a0 [zram]
> >>  printk#14 zram_init+0x22c/0x2a0 [zram]
> >>  printk#15 zram_init+0x22c/0x2a0 [zram]
> >>  printk#16 zram_init+0x22c/0x2a0 [zram]
> >>
> >>I wonder why printk#7 and printk#8 don't show "zram_init"...
> >
> >interesting... what does the unpatched kernel show?
> 
> Really strange.
> The unpatched kernel shows __UNIQUE_ID_vermagic8+0xb9a4/0xbd04 too.
> The symbol should be known, because later on in printk13 it shows correctly zram_init.
> I'll need to dig deeper into it, but at least the regression is not due
> to your patch.

Sergey, I was wrong with this assumption.

Your implementation of dereference_module_function_descriptor() in
arch/parisc/kernel/module.c is faulty.
mod->arch.fdesc_offset is relative to the base address of the module,
so you need to add to mod->core_layout.base.

Here is the relevant patch to fix this issue (against mainline).
Additionally I compare against mod->arch.fdesc_count instead of
mod->arch.fdesc_max.
Can you please fold it into your patch
[PATCH 4/5] parisc64: Add .opd based function descriptor dereference
for the next round?

Thanks,
Helge

Signed-off-by: Helge Deller <deller@....de>

diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index f1a7693..ae3e6c5 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -66,6 +66,7 @@
 
 #include <asm/pgtable.h>
 #include <asm/unwind.h>
+#include <asm/sections.h>
 
 #if 0
 #define DEBUGP printk
@@ -954,3 +955,19 @@ void module_arch_cleanup(struct module *mod)
 {
 	deregister_unwind_table(mod);
 }
+
+#ifdef CONFIG_64BIT
+unsigned long dereference_module_function_descriptor(struct module *mod,
+					     unsigned long addr)
+{
+	unsigned long opd_start = (Elf64_Addr) mod->core_layout.base
+					+ mod->arch.fdesc_offset;
+	unsigned long opd_end = opd_start
+			+ mod->arch.fdesc_count * sizeof(Elf64_Fdesc);
+
+	if (addr < opd_start || addr >= opd_end)
+		return addr;
+
+	return (unsigned long) dereference_function_descriptor((void *) addr);
+}
+#endif