linux-kernel - [PATCH 1/4] scripts/faddr2line: fix "size mismatch" error

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Date:   Tue, 25 Oct 2016 09:51:11 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 1/4] scripts/faddr2line: fix "size mismatch" error

I'm not sure how we missed this problem before.  When I take a function
address and size from an oops and give it to faddr2line, it usually
complains about a size mismatch:

  $ scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  skipping write_sysrq_trigger address at 0xffffffff815731a1 due to size mismatch (0x60 != 83)
  no match for write_sysrq_trigger+0x51/0x60

The problem is caused by differences in how kallsyms and faddr2line
determine a function's size.

kallsyms calculates a function's size by parsing the output of 'nm -n'
and subtracting the next function's address from the current function's
address.  This means that nop instructions after the end of the function
are included in the size.

In contrast, faddr2line reads the size from the symbol table, which does
*not* include the ending nops in the function's size.

Change faddr2line to calculate the size from the output of 'nm -n' to be
consistent with kallsyms and oops outputs.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 scripts/faddr2line | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 450b332..29df825 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -105,9 +105,18 @@ __faddr2line() {
 	# In rare cases there might be duplicates.
 	while read symbol; do
 		local fields=($symbol)
-		local sym_base=0x${fields[1]}
-		local sym_size=${fields[2]}
-		local sym_type=${fields[3]}
+		local sym_base=0x${fields[0]}
+		local sym_type=${fields[1]}
+		local sym_end=0x${fields[3]}
+
+		# calculate the size
+		local sym_size=$(($sym_end - $sym_base))
+		if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
+			warn "bad symbol size: base: $sym_base end: $sym_end"
+			DONE=1
+			return
+		fi
+		sym_size=0x$(printf %x $sym_size)
 
 		# calculate the address
 		local addr=$(($sym_base + $offset))
@@ -116,26 +125,26 @@ __faddr2line() {
 			DONE=1
 			return
 		fi
-		local hexaddr=0x$(printf %x $addr)
+		addr=0x$(printf %x $addr)
 
 		# weed out non-function symbols
-		if [[ $sym_type != "FUNC" ]]; then
+		if [[ $sym_type != t ]] && [[ $sym_type != T ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to non-function symbol"
+				echo "skipping $func address at $addr due to non-function symbol of type '$sym_type'"
 			continue
 		fi
 
 		# if the user provided a size, make sure it matches the symbol's size
 		if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($size != $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
 			continue;
 		fi
 
 		# make sure the provided offset is within the symbol's range
 		if [[ $offset -gt $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($offset > $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
 			continue
 		fi
 
@@ -143,12 +152,12 @@ __faddr2line() {
 		[[ $FIRST = 0 ]] && echo
 		FIRST=0
 
-		local hexsize=0x$(printf %x $sym_size)
-		echo "$func+$offset/$hexsize:"
-		addr2line -fpie $objfile $hexaddr | sed "s; $dir_prefix\(\./\)*; ;"
+		# pass real address to addr2line
+		echo "$func+$offset/$sym_size:"
+		addr2line -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;"
 		DONE=1
 
-	done < <(readelf -sW $objfile | awk -v f=$func '$8 == f {print}')
+	done < <(nm -n $objfile | awk -v fn=$func '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, $1 }')
 }
 
 [[ $# -lt 2 ]] && usage
-- 
2.7.4