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

[Siddhesh Poyarekar]

Ping!

On 7/22/21 6:54 PM, Siddhesh Poyarekar via Libc-alpha wrote:
> 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>
> ---
>   malloc/mtrace-impl.c |  4 ++--
>   malloc/mtrace.pl     | 12 ++++--------
>   2 files changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/malloc/mtrace-impl.c b/malloc/mtrace-impl.c
> index 83008ca18f..3a65863d24 100644
> --- a/malloc/mtrace-impl.c
> +++ b/malloc/mtrace-impl.c
> @@ -65,9 +65,9 @@ tr_where (const void *caller, Dl_info *info)
>   		       offset);
>               }
>   
> -	  fprintf (mallstream, "@ %s%s%s[%p] ", info->dli_fname ? : "",
> +	  fprintf (mallstream, "@ %s%s%s[0x%" PRIxPTR "] ", info->dli_fname ? : "",
>   		   info->dli_fname ? ":" : "",
> -                   buf, caller);
> +                   buf, caller - info->dli_fbase);
>           }
>         else
>           fprintf (mallstream, "@ [%p] ", caller);
> diff --git a/malloc/mtrace.pl b/malloc/mtrace.pl
> index 6f49c8338d..f2570d2186 100644
> --- a/malloc/mtrace.pl
> +++ b/malloc/mtrace.pl
> @@ -75,11 +75,12 @@ if ($#ARGV == 0) {
>       } else {
>   	$prog = "./$binary";
>       }
> -    if (open (LOCS, "env LD_TRACE_LOADED_OBJECTS=1 $prog |")) {
> +    if (open (LOCS, "env LD_TRACE_PRELINKING=1 $prog |")) {
>   	while (<LOCS>) {
>   	    chop;
> -	    if (/^.*=> (.*) .(0x[0123456789abcdef]*).$/) {
> +	    if (/^.*=> (.*) \((0x[0123456789abcdef]*), (0x[0123456789abcdef]*).*/) {
>   		$locs{$1} = $2;
> +		$rel{$1} = hex($2) - hex($3);
>   	    }
>   	}
>   	close (LOCS);
> @@ -110,12 +111,7 @@ 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;
>