[PATCH v2] mtrace: Fix output with PIE and ASLR [BZ #22716]

[PATCH v2] mtrace: Fix output with PIE and ASLR [BZ #22716]

[Siddhesh Poyarekar]

Record only the relative address of the caller in mtrace file.  Use
LD_TRACE_PRELINKING to get the executable as well as binary vs
executable load offsets so that we may compute a base to add to the
relative address in the mtrace file.  This allows us to get a valid
address to pass to addr2line in all cases.

Co-authored-by:  John Ogness <john.ogness@linutronix.de>
---
Changes from v1:
- Set LD_TRACE_PRELINK to an empty string so that it doesn't match any
  files and add a comment explaining it.
- Formatting change in mtrace-impl.c

 malloc/mtrace-impl.c |  6 +++---
 malloc/mtrace.pl     | 15 +++++++--------
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/malloc/mtrace-impl.c b/malloc/mtrace-impl.c
index 6af1a6e01a..23afc9a1df 100644
--- a/malloc/mtrace-impl.c
+++ b/malloc/mtrace-impl.c
@@ -67,9 +67,9 @@ tr_where (const void *caller, Dl_info *info)
 		       offset);
             }
 
-	  fprintf (mallstream, "@ %s%s%s[%p] ", info->dli_fname ? : "",
-		   info->dli_fname ? ":" : "",
-                   buf, caller);
+	  fprintf (mallstream, "@ %s%s%s[0x%" PRIxPTR "] ",
+		   info->dli_fname ? : "", info->dli_fname ? ":" : "", buf,
+		   caller - info->dli_fbase);
         }
       else
         fprintf (mallstream, "@ [%p] ", caller);
diff --git a/malloc/mtrace.pl b/malloc/mtrace.pl
index 6f49c8338d..bdc407122b 100644
--- a/malloc/mtrace.pl
+++ b/malloc/mtrace.pl
@@ -75,11 +75,15 @@ if ($#ARGV == 0) {
     } else {
 	$prog = "./$binary";
     }
-    if (open (LOCS, "env LD_TRACE_LOADED_OBJECTS=1 $prog |")) {
+    # Set the environment variable LD_TRACE_PRELINKING to an empty string so
+    # that we trigger tracing but do not match with the executable or any of
+    # its dependencies.
+    if (open (LOCS, "env LD_TRACE_PRELINKING=\"\" $prog |")) {
 	while (<LOCS>) {
 	    chop;
-	    if (/^.*=> (.*) .(0x[0123456789abcdef]*).$/) {
+	    if (/^.*=> (.*) \((0x[0123456789abcdef]*), (0x[0123456789abcdef]*).*/) {
 		$locs{$1} = $2;
+		$rel{$1} = hex($2) - hex($3);
 	    }
 	}
 	close (LOCS);
@@ -110,12 +114,7 @@ sub location {
 	my $addr = $2;
 	my $searchaddr;
 	return $cache{$addr} if (exists $cache{$addr});
-	if ($locs{$prog} ne "") {
-	    $searchaddr = sprintf "%#x", $addr - $locs{$prog};
-	} else {
-	    $searchaddr = $addr;
-	    $prog = $binary;
-	}
+	$searchaddr = sprintf "%#x", hex($addr) + $rel{$prog};
 	if ($binary ne "" && open (ADDR, "addr2line -e $prog $searchaddr|")) {
 	    my $line = <ADDR>;
 	    chomp $line;
-- 
2.31.1

Re: [PATCH v2] mtrace: Fix output with PIE and ASLR [BZ #22716]

[Andreas Schwab]

On Aug 12 2021, Siddhesh Poyarekar via Libc-alpha wrote:

> +    if (open (LOCS, "env LD_TRACE_PRELINKING=\"\" $prog |")) {

No need for "".

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."