gdb: improve error reporting for 'save gdb-index'

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

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
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.

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


base-commit: 2c4caca9873ef4e97a51a538dfbecde8fe334082
  

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