Re: [PATCH][gdb/testsuite] Fail in gdb_compile if nopie results in PIE executable

[Alan Hayward <Alan.Hayward@arm.com>]

> On 23 Jul 2019, at 08:22, Tom de Vries <tdevries@suse.de> wrote:
> 
> Hi,
> 
> When running gdb.base/dump.exp with --target_board=unix/-fPIE/-pie, we get:
> ...
> Running gdb/testsuite/gdb.base/dump.exp ...
> FAIL: gdb.base/dump.exp: dump array as value, intel hex
> ...
> 
> The FAIL happens because although the test specifies nopie, the exec is
> in fact compiled as PIE.  The "-fPIE -pie" options specified using the
> target_board are interpreted by dejagnu as multilib_flags, and end up
> overriding the nopie flags.
> 
> Fix this by checking in gdb_compile if the resulting exec is PIE despite of
> a nopie setting, and if so return an error:
> ...
> Running gdb/testsuite/gdb.base/dump.exp ...
> gdb compile failed, nopie failed to prevent PIE executable
> 
>                === gdb Summary ===
> 
> nr of untested testcases         1
> ...
> 
> Tested on x86_64-linux.
> 
> OK for trunk?

LGTM (but I’m not a global maintainer).

I tried this on an Ubuntu18.04 (which defaults gcc to use PIE), and everything
looks fine.


> 
> Thanks,
> - Tom
> 
> [gdb/testsuite] Fail in gdb_compile if nopie results in PIE executable
> 
> 2019-07-23  Tom de Vries  <tdevries@suse.de>
> 
> 	PR testsuite/24834
> 	* lib/gdb.exp (gdb_compile): Fail if nopie results in PIE executable.
> 	(exec_is_pie): New proc.
> 
> ---
> gdb/testsuite/lib/gdb.exp | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
> 
> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index 49ec8b2a55..5ec0912325 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -3760,6 +3760,12 @@ proc gdb_compile {source dest type options} {
>     regsub "\[\r\n\]*$" "$result" "" result
>     regsub "^\[\r\n\]*" "$result" "" result
> 
> +    if { $type == "executable" && $result == "" && $nopie != -1 } {
> +	if { [exec_is_pie "$dest"] } {
> +	    set result "nopie failed to prevent PIE executable"
> +	}
> +    }
> +

As a side point, I just spotted that if a script specifies both pie and nopie, then
I think it ends up as nopie because the nopie flag gets set second.
Maybe it should error if both options are sent to gdb_compile.
Not something that needs fixing with this patch though.


>     if {[lsearch $options quiet] < 0} {
> 	# We shall update this on a per language basis, to avoid
> 	# changing the entire testsuite in one go.
> @@ -5160,6 +5166,18 @@ proc exec_has_index_section { executable } {
>     return 0
> }
> 
> +# Return true if EXECUTABLE is a Position Independent Executable.
> +
> +proc exec_is_pie { executable } {
> +    set readelf_program [gdb_find_readelf]
> +    set res [catch {exec $readelf_program -d $executable \
> +			| grep -E "(FLAGS_1).*Flags:.* PIE($| )" }]
> +    if { $res == 0 } {
> +	return 1
> +    }
> +    return 0
> +}
> +
> # Return true if a test should be skipped due to lack of floating
> # point support or GDB can't fetch the contents from floating point
> # registers.