linux-kernel - [PATCH] ARM: mm: Facilitate debugging CONFIG_KUSER

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Date:   Thu, 25 Oct 2018 11:09:55 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     andrew@...n.ch, Florian Fainelli <f.fainelli@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Tony Lindgren <tony@...mide.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] ARM: mm: Facilitate debugging CONFIG_KUSER_HELPERS disabled

Some software such as perf makes unconditional use of the special
[vectors] page which is only provided when CONFIG_KUSER_HELPERS is
enabled in the kernel.

Facilitate the debugging of such situations by printing a debug message
to the kernel log showing the task name and the faulting address.

Suggested-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 arch/arm/mm/fault.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index f4ea4c62c613..f17471fbc1c4 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned long addr,
 		show_regs(regs);
 	}
 #endif
+#ifndef CONFIG_KUSER_HELPERS
+	if ((sig == SIGSEGV) && ((addr & PAGE_MASK) == 0xffff0000))
+		printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at 0x%08lx\n",
+		       tsk->comm, addr);
+#endif
 
 	tsk->thread.address = addr;
 	tsk->thread.error_code = fsr;
-- 
2.17.1