Re: [PATCH] gdb: improve error reporting for 'save gdb-index'

[Tom de Vries <tdevries@suse.de>]

On 12/4/23 20:29, Andrew Burgess wrote:
> While making recent changes to 'save gdb-index' command I triggered
> some errors -- of the kind a user might be expected to trigger if they
> do something wrong -- and I didn't find GDB's output as helpful as it
> might be.
> 
> For example:
> 
>    $ gdb -q /tmp/hello.x
>    ...
>    (gdb) save gdb-index /non_existing_dir
>    Error while writing index for `/tmp/hello': mkstemp: No such file or directory.
> 
> That the error message mentions '/tmp/hello', which does exit, but

exit -> exist

> doesn't mention '/non_existing_dir', which doesn't is, I think,
> confusing.
> 

Agreed.

> Also, I find the 'mkstemp' in the error message confusing for a user
> facing error.  A user might not know what mkstemp means, and even if
> they do, that it appears in the error message is an internal GDB
> detail.  The user doesn't care what function failed, why want to know

why want -> but wants ?

> what was wrong with their input, and what they should do to fix
> things.
> 
> Similarly, for a directory that does exist, but can't be written to:
> 
>    (gdb) save gdb-index /no_access_dir
>    Error while writing index for `/tmp/hello': mkstemp: Permission denied.
> 
> In this case, the 'Permission denied' might make the user thing there
> is a permissions issue with '/tmp/hello', which is not the case.
> 
> After this patch, the new errors are:
> 
>    (gdb) save gdb-index /non_existing_dir
>    Error while writing index for `/tmp/hello': `/non_existing_dir': No such file or directory.
> 
> and:
> 
>    (gdb) save gdb-index /no_access_dir
>    Error while writing index for `/tmp/hello': `/no_access_dir': Permission denied.
> 
> we also have:
> 
>    (gdb) save gdb-index /tmp/not_a_directory
>    Error while writing index for `/tmp/hello': `/tmp/not_a_directory': Is not a directory.
> 
> I think these do a better job of guiding the user towards fixing the
> problem.
> 

Agreed, I think this is a nice improvement.

> I've added a new test that exercises all of these cases, and also
> checks the case where a user tries to use an executable that already
> contains an index in order to generate an index.
> 
> Nothing that worked correctly before this patch should give an error
> after this patch; I've only changed the output when the user was going
> to get an error anyway.
> ---
>   gdb/dwarf2/index-write.c                 |  10 +-
>   gdb/testsuite/gdb.base/gdb-index-err.c   |  22 +++++
>   gdb/testsuite/gdb.base/gdb-index-err.exp | 118 +++++++++++++++++++++++
>   3 files changed, 149 insertions(+), 1 deletion(-)
>   create mode 100644 gdb/testsuite/gdb.base/gdb-index-err.c
>   create mode 100644 gdb/testsuite/gdb.base/gdb-index-err.exp
> 
> diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
> index b4a0117330e..4e5490e734e 100644
> --- a/gdb/dwarf2/index-write.c
> +++ b/gdb/dwarf2/index-write.c
> @@ -1569,6 +1569,13 @@ struct index_wip_file
>     index_wip_file (const char *dir, const char *basename,
>   		  const char *suffix)
>     {
> +    /* Validate DIR is a  valid directory.  */

double space.

> +    struct stat buf;
> +    if (stat (dir, &buf) == -1)
> +      perror_with_name (string_printf (_("`%s'"), dir).c_str ());
> +    if ((buf.st_mode & S_IFDIR) != S_IFDIR)
> +      error (_("`%s': Is not a directory."), dir);
> +
>       filename = (std::string (dir) + SLASH_STRING + basename
>   		+ suffix);
>   
> @@ -1577,7 +1584,8 @@ struct index_wip_file
>       scoped_fd out_file_fd = gdb_mkostemp_cloexec (filename_temp.data (),
>   						  O_BINARY);
>       if (out_file_fd.get () == -1)
> -      perror_with_name (("mkstemp"));
> +      perror_with_name (string_printf (_("couldn't open `%s'"),
> +				       filename_temp.data ()).c_str ());
>   
>       out_file = out_file_fd.to_file ("wb");
>   
> diff --git a/gdb/testsuite/gdb.base/gdb-index-err.c b/gdb/testsuite/gdb.base/gdb-index-err.c
> new file mode 100644
> index 00000000000..3a264f239ed
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/gdb-index-err.c
> @@ -0,0 +1,22 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> +   Copyright 2023 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +int
> +main ()
> +{
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.base/gdb-index-err.exp b/gdb/testsuite/gdb.base/gdb-index-err.exp
> new file mode 100644
> index 00000000000..9493c3aafd2
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/gdb-index-err.exp
> @@ -0,0 +1,118 @@
> +# Copyright 2023 Free Software Foundation, Inc.
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Test some error messages that can arise from the 'save gdb-index'
> +# command.
> +
> +standard_testfile
> +
> +if {[build_executable "build executable" $testfile $srcfile] == -1} {
> +    return -1
> +}
> +
> +clean_restart $binfile
> +

I think the usual shorthand for this is prepare_for_testing.

> +# This test isn't going to work when the board file automatically adds
> +# an index section, or if the debug information is split into a
> +# separate objfile.
> +set has_cooked_index false
> +gdb_test_multiple "maint print objfiles ${binfile}" "check debug style" -lbl {
> +    -re "\r\n\\.gdb_index: version ${decimal}(?=\r\n)" {
> +	gdb_test_lines "" $gdb_test_name ".*"
> +    }
> +    -re "\r\n\\.debug_names: exists(?=\r\n)" {
> +	gdb_test_lines "" $gdb_test_name ".*"
> +    }
> +    -re "\r\n(Cooked index in use:|Psymtabs)(?=\r\n)" {
> +	set has_cooked_index true
> +	gdb_test_lines "" $gdb_test_name ".*"
> +    }
> +    -re ".gdb_index: faked for \"readnow\"" {
> +	gdb_test_lines "" $gdb_test_name ".*"
> +    }
> +    -re -wrap "" {
> +	# Have no debug information!
> +    }
> +}
> +

I think ideally we do this kind of checks using a factored out function 
in gdb.exp.  There may already be one, I haven't checked.  If not, maybe 
consider moving it there.

Anyway, LGTM.

Reviewed-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom

> +if { !$has_cooked_index } {
> +    unsupported "cannot test without a cooked index"
> +    return -1
> +}
> +
> +
> +# The name of a directory that doesn't exist.
> +set bad_dir [standard_output_file "non-existent"]
> +
> +# Try to write the index into a non-existent directory.
> +foreach_with_prefix flag { "" "-dwarf-5" } {
> +    gdb_test "save gdb-index ${flag} ${bad_dir}" \
> +	"Error while writing index for `[string_to_regexp $binfile]': `[string_to_regexp $bad_dir]': No such file or directory\\." \
> +	"try to write index to non-existent directory"
> +}
> +
> +# Create a text-file.
> +set text_file [standard_output_file "text-file"]
> +set fd [open $text_file w]
> +puts $fd "A line of text.\n"
> +close $fd
> +
> +# Try to write the index into something that is not a directory.
> +foreach_with_prefix flag { "" "-dwarf-5" } {
> +    gdb_test "save gdb-index ${flag} ${text_file}" \
> +	"Error while writing index for `[string_to_regexp $binfile]': `[string_to_regexp $text_file]': Is not a directory\\." \
> +	"try to write index to something that's not a directory"
> +}
> +
> +# Create a directory which can't be written too.
> +set non_writable_dir [standard_output_file "private"]
> +remote_exec host "mkdir -p ${non_writable_dir}"
> +remote_exec host "chmod u-w,g-w ${non_writable_dir}"
> +
> +# Try to write the index into a non-writable directory.
> +foreach_with_prefix flag { "" "-dwarf-5" } {
> +    gdb_test "save gdb-index ${flag} ${non_writable_dir}" \
> +	"Error while writing index for `[string_to_regexp $binfile]': couldn't open `[string_to_regexp $non_writable_dir]/${gdb_test_file_name}.*': Permission denied\\." \
> +	"try to write index to a non-writable directory"
> +}
> +
> +# Create copies of the executable, we will add an index section to
> +# each of these.
> +remote_exec host "cp $binfile ${binfile}.gdb_index"
> +remote_exec host "cp $binfile ${binfile}.dwarf_5"
> +
> +# Create a directory in which we can try to generate the index files.
> +set already_indexed_dir [standard_output_file "already_indexed"]
> +remote_exec host "mkdir -p $already_indexed_dir"
> +
> +foreach_with_prefix flag { "" "-dwarf-5" } {
> +    if { $flag eq "" } {
> +	set extension "gdb_index"
> +    } else {
> +	set extension "dwarf_5"
> +    }
> +
> +    # Add the index section to the executable.
> +    clean_restart ${binfile}.${extension}
> +    gdb_assert {[ensure_gdb_index ${binfile}.${extension} ${flag}] == 1} \
> +	"add index to executable"
> +
> +    # Reload the executable (which now has an index), and try to
> +    # generate and index from it.  This will fail.
> +    clean_restart ${binfile}.${extension}
> +    gdb_test "save gdb-index ${flag} $already_indexed_dir" \
> +	"Error while writing index for `[string_to_regexp $binfile.$extension]': Cannot use an index to create the index" \
> +	"try to generate an index from a binary with an index"
> +}
> 
> base-commit: 2c4caca9873ef4e97a51a538dfbecde8fe334082