[2/3] malloc: Remove LD_TRACE_PRELINKING usage from mtrace

The fix for BZ#22716 replaced LD_TRACE_LOADED_OBJECTS with
LD_TRACE_PRELINKING so mtrace could record executable address
as well.

To provide the same information, LD_TRACE_LOADED_OBJECTS is
extended where a value or '2' also prints the executable address.
It avoid adding another loader environment variable to be used 
solely for mtrace.  The vDSO will be printed as a default library
(with '=>' pointing the same name), which is ok since both mtrace
and ldd already handles it.

The mtrace script is changed to also parse the new format.  To
correctly support PIE and non-PIE executables, both the default
mtrace address and the one calculated as used (it fixes mtrace
for non-PIE exectuable as for BZ#22716 for PIE).

Checked on x86_64-linux-gnu.
---
 elf/dl-main.h    |  3 +++
 elf/rtld.c       | 22 +++++++++++--------
 malloc/mtrace.pl | 55 +++++++++++++++++++++++++++---------------------
 3 files changed, 47 insertions(+), 33 deletions(-)

On 21/01/2022 22:59, Adhemerval Zanella via Libc-alpha wrote:
> The fix for BZ#22716 replaced LD_TRACE_LOADED_OBJECTS with
> LD_TRACE_PRELINKING so mtrace could record executable address
> as well.
> 
> To provide the same information, LD_TRACE_LOADED_OBJECTS is
> extended where a value or '2' also prints the executable address.
> It avoid adding another loader environment variable to be used
> solely for mtrace.  The vDSO will be printed as a default library
> (with '=>' pointing the same name), which is ok since both mtrace
> and ldd already handles it.
> 
> The mtrace script is changed to also parse the new format.  To
> correctly support PIE and non-PIE executables, both the default
> mtrace address and the one calculated as used (it fixes mtrace
> for non-PIE exectuable as for BZ#22716 for PIE).
> 
> Checked on x86_64-linux-gnu.

Looks mostly OK, just a nit below.  Please also enhance the NEWS entry 
in 1/3 to mention the changes in environment variables (i.e. removed 
LD_TRACE_PRELINKING and new value for LD_TRACE_LOADED_OBJECTS).

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> ---
>   elf/dl-main.h    |  3 +++
>   elf/rtld.c       | 22 +++++++++++--------
>   malloc/mtrace.pl | 55 +++++++++++++++++++++++++++---------------------
>   3 files changed, 47 insertions(+), 33 deletions(-)
> 
> diff --git a/elf/dl-main.h b/elf/dl-main.h
> index 3e32f254c5..e4fa19ee4e 100644
> --- a/elf/dl-main.h
> +++ b/elf/dl-main.h
> @@ -94,6 +94,9 @@ struct dl_main_state
>   
>     enum rtld_mode mode;
>   
> +  /* True if program should be also printed for rtld_mode_trace.  */
> +  bool mode_trace_program;
> +
>     /* True if any of the debugging options is enabled.  */
>     bool any_debug;
>   
> diff --git a/elf/rtld.c b/elf/rtld.c
> index dbf40c6bc1..9fea138619 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -2103,18 +2103,18 @@ dl_main (const ElfW(Phdr) *phdr,
>   	_dl_printf ("\tstatically linked\n");
>         else
>   	{
> -	  for (l = main_map->l_next; l; l = l->l_next)
> +	  for (l = state.mode_trace_program ? main_map : main_map->l_next;
> +	       l; l = l->l_next) {
>   	    if (l->l_faked)
>   	      /* The library was not found.  */
> -	      _dl_printf ("\t%s => not found\n", l->l_libname->name);
> -	    else if (strcmp (l->l_libname->name, l->l_name) == 0)
> -	      _dl_printf ("\t%s (0x%0*Zx)\n", l->l_libname->name,
> -			  (int) sizeof l->l_map_start * 2,
> -			  (size_t) l->l_map_start);
> +	      _dl_printf ("\t%s => not found\n",  l->l_libname->name);
>   	    else
> -	      _dl_printf ("\t%s => %s (0x%0*Zx)\n", l->l_libname->name,
> -			  l->l_name, (int) sizeof l->l_map_start * 2,
> +	      _dl_printf ("\t%s => %s (0x%0*Zx)\n",
> +			  DSO_FILENAME (l->l_libname->name),
> +			  DSO_FILENAME (l->l_name),
> +			  (int) sizeof l->l_map_start * 2,
>   			  (size_t) l->l_map_start);
> +	  }
>   	}

Also print address for main_map if tracing.  OK.

>   
>         if (__glibc_unlikely (state.mode != rtld_mode_trace))
> @@ -2675,7 +2675,11 @@ process_envvars (struct dl_main_state *state)
>   	case 20:
>   	  /* The mode of the dynamic linker can be set.  */
>   	  if (memcmp (envline, "TRACE_LOADED_OBJECTS", 20) == 0)
> -	    state->mode = rtld_mode_trace;
> +	    {
> +	      state->mode = rtld_mode_trace;
> +	      state->mode_trace_program
> +		= _dl_strtoul (&envline[21], NULL) > 1;
> +	    }
>   	  break;
>   
>   	  /* We might have some extra environment variable to handle.  This
> diff --git a/malloc/mtrace.pl b/malloc/mtrace.pl
> index 042df725eb..bd2755ca77 100644
> --- a/malloc/mtrace.pl
> +++ b/malloc/mtrace.pl
> @@ -74,15 +74,14 @@ if ($#ARGV == 0) {
>       } else {
>   	$prog = "./$binary";
>       }
> -    # 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>) {
> +    # Set the environment variable LD_TRACE_LOADED_OBJETS to 2 so the

s/LD_TRACE_LOADED_OBJETS/LD_TRACE_LOADED_OBJECTS/

> +    # executable is also printed.
> +    if (open (locs, "env LD_TRACE_LOADED_OBJECTS=2 $prog |")) {
> +	while (<locs>) {
>   	    chop;
> -	    if (/^.*=> (.*) \((0x[0123456789abcdef]*), (0x[0123456789abcdef]*).*/) {
> +	    if (/^.*=> (.*) .(0x[0123456789abcdef]*).$/) {
>   		$locs{$1} = $2;
> -		$rel{$1} = hex($2) - hex($3);
> +		$rel{$1} = hex($2);

OK.

>   	    }
>   	}
>   	close (LOCS);
> @@ -91,6 +90,18 @@ if ($#ARGV == 0) {
>       die "Wrong number of arguments, run $progname --help for help.";
>   }
>   
> +sub addr2line {
> +    my $addr = pop(@_);
> +    my $prog = pop(@_);
> +    if (open (ADDR, "addr2line -e $prog $addr|")) {
> +	my $line = <ADDR>;
> +	chomp $line;
> +	close (ADDR);
> +	if ($line ne '??:0') {
> +	    return $line
> +	}
> +    }
> +}

Consolidated addr2line invocation.  OK.

>   sub location {
>       my $str = pop(@_);
>       return $str if ($str eq "");
> @@ -98,11 +109,9 @@ sub location {
>   	my $addr = $1;
>   	my $fct = $2;
>   	return $cache{$addr} if (exists $cache{$addr});
> -	if ($binary ne "" && open (ADDR, "addr2line -e $binary $addr|")) {
> -	    my $line = <ADDR>;
> -	    chomp $line;
> -	    close (ADDR);
> -	    if ($line ne '??:0') {
> +	if ($binary ne "") {
> +	    my $line = &addr2line($binary, $addr);
> +	    if ($line) {
>   		$cache{$addr} = $line;
>   		return $cache{$addr};
>   	    }
> @@ -114,24 +123,22 @@ sub location {
>   	my $searchaddr;
>   	return $cache{$addr} if (exists $cache{$addr});
>   	$searchaddr = sprintf "%#x", hex($addr) + $rel{$prog};
> -	if ($binary ne "" && open (ADDR, "addr2line -e $prog $searchaddr|")) {
> -	    my $line = <ADDR>;
> -	    chomp $line;
> -	    close (ADDR);
> -	    if ($line ne '??:0') {
> -		$cache{$addr} = $line;
> -		return $cache{$addr};
> +	if ($binary ne "") {
> +	    for my $address ($searchaddr, $addr) {
> +		my $line = &addr2line($prog, $address);
> +		if ($line) {
> +		    $cache{$addr} = $line;
> +		    return $cache{$addr};
> +		}
>   	    }
>   	}
>   	$cache{$addr} = $str = $addr;
>       } elsif ($str =~ /^.*[[](0x[^]]*)]$/) {
>   	my $addr = $1;
>   	return $cache{$addr} if (exists $cache{$addr});
> -	if ($binary ne "" && open (ADDR, "addr2line -e $binary $addr|")) {
> -	    my $line = <ADDR>;
> -	    chomp $line;
> -	    close (ADDR);
> -	    if ($line ne '??:0') {
> +	if ($binary ne "") {
> +	    my $line = &addr2line($binary, $addr);
> +	    if ($line) {
>   		$cache{$addr} = $line;
>   		return $cache{$addr};
>   	    }