[3.13.y-ckt stable] Patch "ARC: dw2 unwind: Ignore CIE version !=1 gracefully instead of bailing" has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ARC: dw2 unwind: Ignore CIE version !=1 gracefully instead of bailing

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt33.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From e7e3ce23ccd709ae341ab0e555d116acb75913ab Mon Sep 17 00:00:00 2001
From: Vineet Gupta <vgupta at synopsys.com>
Date: Wed, 16 Dec 2015 17:17:00 +0530
Subject: ARC: dw2 unwind: Ignore CIE version !=1 gracefully instead of bailing

commit 323f41f9e7d0cb5b1d1586aded6682855f1e646d upstream.

ARC dwarf unwinder only supports CIE version == 1
The boot time dwarf sanitizer (part of binary lookup table constructor)
would simply bail if it saw CIE version == 3, rendering unwinder with a
NULL lookup table.

It seems libgcc linked with kernel does have such entries.

With fallback linear search removed, and a NULL binary lookup table,
unwinder fails to generate any stack trace.

So allow graceful ignoring of unsupported CIE entries.

This problem was initially seen in Alexey's setup (and not mine) as he
was using buildroot built toolchain (libgcc) which doesn't get built with
CFLAGS_FOR_TARGET="-gdwarf-2 which is my default

Fixes STAR 9000985048: "kernel unwinder broken with stock tools"

Fixes: 2e22502c080f ARC: dw2 unwind: Remove falllback linear search thru FDE entries
Reported-by Alexey Brodkin <abrodkin at synopsys.com>
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arc/kernel/unwind.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c
index 5c1d071..9bfbd0a 100644
--- a/arch/arc/kernel/unwind.c
+++ b/arch/arc/kernel/unwind.c
@@ -293,13 +293,13 @@ static void init_unwind_hdr(struct unwind_table *table,
 		const u32 *cie = cie_for_fde(fde, table);
 		signed ptrType;

-		if (cie == &not_fde)
+		if (cie == &not_fde)	/* only process FDE here */
 			continue;
 		if (cie == NULL || cie == &bad_cie)
-			return;
+			continue;	/* say FDE->CIE.version != 1 */
 		ptrType = fde_pointer_type(cie);
 		if (ptrType < 0)
-			return;
+			continue;

 		ptr = (const u8 *)(fde + 2);
 		if (!read_pointer(&ptr, (const u8 *)(fde + 1) + *fde,
@@ -343,6 +343,10 @@ static void init_unwind_hdr(struct unwind_table *table,

 		if (fde[1] == 0xffffffff)
 			continue;	/* this is a CIE */
+
+		if (*(u8 *)(cie + 2) != 1)
+			continue;	/* FDE->CIE.version not supported */
+
 		ptr = (const u8 *)(fde + 2);
 		header->table[n].start = read_pointer(&ptr,
 						      (const u8 *)(fde + 1) +
@@ -519,7 +523,8 @@ static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *table)

 	if (*cie <= sizeof(*cie) + 4 || *cie >= fde[1] - sizeof(*fde)
 	    || (*cie & (sizeof(*cie) - 1))
-	    || (cie[1] != 0xffffffff))
+	    || (cie[1] != 0xffffffff)
+	    || ( *(u8 *)(cie + 2) != 1))   /* version 1 supported */
 		return NULL;	/* this is not a (valid) CIE */
 	return cie;
 }
--
1.9.1