Re: [PATCH v3 02/14] Change gdb.base/skip-solib.exp deal with lack of epilogue information

[Andrew Burgess <aburgess@redhat.com>]

Bruno Larsen via Gdb-patches <gdb-patches@sourceware.org> writes:

> When running gdb.base/skip-solib.exp, the backtrace tests could fail if
> the compiler did not emit epilogue information for trivial epilogues,
> despite the feature being fully functional.  As an example, when testing
> skipping the function square, the testsuite would show
>
> Breakpoint 1, main () at (...)/binutils-gdb/gdb/testsuite/gdb.base/skip-solib-main.c:5
> 5         return square(0);
> (gdb) step
> 0x00007ffff7cef560 in __libc_start_call_main () from /lib64/libc.so.6
> (gdb) PASS: gdb.base/skip-solib.exp: ignoring solib file: step
> bt
>  #0  0x00007ffff7cef560 in __libc_start_call_main () from /lib64/libc.so.6
>  #1  0x00007ffff7cef60c in __libc_start_main_impl () from /lib64/libc.so.6
>  #2  0x0000000000401065 in _start ()
> (gdb) FAIL: gdb.base/skip-solib.exp: ignoring solib file: bt
>
> Which means that the feature is working, the testsuite is just
> mis-identifying it.  To avoid this problem, the skipped function calls
> have been sent to a line before `return`, so epilogues won't factor in.
>
> This commit has also changed a few hardcoded steps to leave functions to
> the newly introduced gdb_step_until_regexp to leave those functions.
> ---
>
> No change in v3
>
> v2: chagned to use step_until_regexp instead of finish
>
> ---
>  gdb/testsuite/gdb.base/skip-inline.exp   | 18 +++++++++++-------
>  gdb/testsuite/gdb.base/skip-solib-lib.c  |  3 ++-
>  gdb/testsuite/gdb.base/skip-solib-main.c |  3 ++-
>  gdb/testsuite/gdb.base/skip-solib.exp    | 12 ++++++++++--
>  4 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.base/skip-inline.exp b/gdb/testsuite/gdb.base/skip-inline.exp
> index f6e9926b66c..327ea676140 100644
> --- a/gdb/testsuite/gdb.base/skip-inline.exp
> +++ b/gdb/testsuite/gdb.base/skip-inline.exp
> @@ -35,16 +35,20 @@ gdb_test "skip function foo" "Function foo will be skipped when stepping\."
>  gdb_test "bt" "\\s*\\#0\\s+main.*" "in the main"
>  gdb_test "step" ".*" "step into baz, since foo will be skipped"
>  gdb_test "bt" "\\s*\\#0\\s+baz.*" "in the baz, since foo was skipped"
> -gdb_test "step" ".*" "step in the baz"
> -gdb_test "bt" "\\s*\\#0\\s+baz.*" "still in the baz"
> -gdb_test "step" ".*" "step back to main"
> +gdb_step_until_regexp ".*x = 0; x = baz \\(foo \\(\\)\\).*"
>  gdb_test "bt" "\\s*\\#0\\s+main.*" "again in the main"
>  gdb_test "step" ".*" "step again into baz, since foo will be skipped"
>  gdb_test "bt" "\\s*\\#0\\s+baz.*" "again in the baz"
> -gdb_test "step" ".*" "step in the baz, again"
> -gdb_test "bt" "\\s*\\#0\\s+baz.*" "still in the baz, again"
> -gdb_test "step" ".*" "step back to main, again"
> -gdb_test "bt" "\\s*\\#0\\s+main.*" "again back to main"
> +gdb_step_until_regexp "main \\(\\) at .*" "step back to main, again"
> +gdb_test "bt" "\\s*\\#0.*main.*" "again back to main"
> +
> +# because clang doesn't add epilogue information, having a set number of

Capital letter - 'Because'.

> +# steps puts clang more and more out of sync with gcc.  It is unlikely that
> +# the effort of keeping both outputs will be useful.
> +if {[test_compiler_info "clang-*"]} {
> +    untested "Multiple steps are not supported with clang"

I'd reword this as "Multiple step tests are not supported with clang"
just to avoid confusion.  Multiple steps are fine, it's the tests
themselves we're not proposing to support with clang.

> +    return
> +}
>  
>  if ![runto_main] {
>      return
> diff --git a/gdb/testsuite/gdb.base/skip-solib-lib.c b/gdb/testsuite/gdb.base/skip-solib-lib.c
> index b2c4d86d703..341f1440a3b 100644
> --- a/gdb/testsuite/gdb.base/skip-solib-lib.c
> +++ b/gdb/testsuite/gdb.base/skip-solib-lib.c
> @@ -7,5 +7,6 @@ int multiply(int a, int b)
>  
>  int square(int num)
>  {
> -  return multiply(num, num);
> +  int res = multiply(num, num);
> +  return res;
>  }
> diff --git a/gdb/testsuite/gdb.base/skip-solib-main.c b/gdb/testsuite/gdb.base/skip-solib-main.c
> index 746bb5f36bb..a3b6d417935 100644
> --- a/gdb/testsuite/gdb.base/skip-solib-main.c
> +++ b/gdb/testsuite/gdb.base/skip-solib-main.c
> @@ -2,5 +2,6 @@ int square(int num);
>  
>  int main()
>  {
> -  return square(0);
> +  int s = square(0);
> +  return s;
>  }
> diff --git a/gdb/testsuite/gdb.base/skip-solib.exp b/gdb/testsuite/gdb.base/skip-solib.exp
> index 0f2ce7e1ad8..8e61725ad1b 100644
> --- a/gdb/testsuite/gdb.base/skip-solib.exp
> +++ b/gdb/testsuite/gdb.base/skip-solib.exp
> @@ -82,7 +82,7 @@ with_test_prefix "ignoring solib file" {
>      # We shouldn't step into square(), since we skipped skip-solib-lib.c.
>      #
>      gdb_test "step" ""
> -    gdb_test "bt" "#0\\s+main.*"
> +    gdb_test "bt 1" "#0\\s+main.*"

I don't object to this change, but it's not necessary.

>  }
>  
>  #
> @@ -114,5 +114,13 @@ with_test_prefix "ignoring solib function" {
>      # the last line of square.
>      #
>      gdb_test "step" ""
> -    gdb_test "bt" "#0\\s+square.*"
> +    gdb_test "bt 1" "#0\\s+square.*" "skipped multiply"
> +#    gdb_test_multiple "bt 1" "skipped multiply" {
> +#	-re "#0\\s+square.*" {
> +#	    pass "skipped multiply"
> +#	}
> +#	-re "#0.*main.*" {
> +#	    pass "skipped multiply"
> +#	}
> +#    }

So, I was worried while looking at this change that we might end up
removing all the places where we try to step through code like:

  int square(int num)
  {
    return multiply(num, num);
  }

Which I think would be a shame.  However, I notice you (accidentally)
left in some commented out code - and I think we might be able to use
that.

What if we reverted the change to the `square` function, and then, for
this last test did this:

    gdb_test_multiple "bt 1" "skipped multiply" {
	-re "#0\\s+square.*" {
	    pass $gdb_test_name
	}
	-re "#0.*main.*" {
	    # Clang doesn't add sufficient epilogue information to
	    # allow GDB to stop within square after the call to
	    # multiply.  We accept ending up back in main, but only
	    # for clang.
	    if [test_compiler_info clang*] {
		pass $gdb_test_name
	    }
	}
    }

For any compiler that, like gcc, emits some line info for the function
epilogue, the test passes.  But we let clang pass even though it appears
to unwind the extra frame.

Thoughts?

Thanks,
Andrew