gas: Add --compress-debug-sections=force
Checks
Commit Message
[ was: Re: [PATCH] gas: Add --force-compress-debug-sections ]
On 2/27/23 10:03, Jan Beulich wrote:
> On 24.02.2023 15:57, Tom de Vries wrote:
>> On 2/24/23 15:26, Jan Beulich wrote:
>>> On 24.02.2023 15:11, Tom de Vries wrote:
>>>> On 2/24/23 14:23, Jan Beulich wrote:
>>>>> On 24.02.2023 13:21, Tom de Vries wrote:
>>>>>> On 2/24/23 12:28, Jan Beulich wrote:
>>>>>>> I also wouldn't see anything wrong with something
>>>>>>> like "...=force,zstd,none" - the last one(s) win. That's no different
>>>>>>> from specifying a second instance of the option. And without that it
>>>>>>> looks as if the parsing would end up simpler.
>>>>>>
>>>>>> OK, gave that a try.
>>>>>
>>>>> That's still accumulating none and force across the entire sequence
>>>>> (and then giving none priority over force, no matter that force may
>>>>> have been specified last),
>>>>
>>>> Um, so you're saying that none+zstd+force is currently interpreted as none?
>>>>
>>>> Lets try:
>>>> ...
>>>> $ gcc ~/hello.c -c -Wa,-gdwarf-5 -Xassembler
>>>> --compress-debug-sections=none+zstd+force
>>>> $ readelf -S -W hello.o | grep " .debug"
>>>> [ 9] .debug_line PROGBITS 0000a8 000064 00 C 0 0 8
>>>> [11] .debug_line_str PROGBITS 000110 000046 01 MSC 0 0 8
>>>> [12] .debug_info PROGBITS 000158 000046 00 C 0 0 8
>>>> [14] .debug_abbrev PROGBITS 0001a0 000049 00 C 0 0 8
>>>> [15] .debug_aranges PROGBITS 0001f0 000034 00 C 0 0 8
>>>> [17] .debug_str PROGBITS 000228 00005a 01 MSC 0 0 8
>>>>
>>>> ...
>>>>
>>>> So, that doesn't seem to be the case, compression is done, as expected.
>>>
>>> Oh, I've overlooked that you explicitly clear *none when you set *force
>>> (my attention was mainly on the bottom of parse_compress_debug_optarg()).
>>> I think that's more involved than necessary (possibly merely a result of
>>> you having worked incrementally from your earlier version), and less
>>> obviously doing the same as would happen when multiple separate options
>>> were parsed.
>>
>> I've tried to simplify further.
>>
>> Is this more how you want it?
>
> I have to admit that I'm still puzzled by the presence of
> finalize_parse_compress_debug_optarg() as well as you needing both a new
> static variable and a new global one.
The latter I've fixed, by exporting the static variable.
That eliminates one half of finalize_parse_compress_debug_optarg().
The remaining half is necessary because we accumulate "none" into
compress_debug_action instead of into flag_compress_debug, so after
parsing is over we need to assign the accumulation result, if it is
indeed cda_none, to flag_compress_debug.
And the reason we have that complicated setup is related to preventing
none from zapping compression type.
> But I guess whether that's really
> needed first of all depends on the semantics we want e.g.
>
> --nocompress-debug-sections --compress-debug-sections=force
>
> to have (which, with how you have it presently, could also be expressed
> as
>
> --compress-debug-sections=none+force
>
> or
>
> --compress-debug-sections=none --compress-debug-sections=force
>
> afaict). I view the present meaning as one sensible one, but I could
> also see "none" (or equivalent) simply zapping the compression type
> (and hence rendering "force" meaningless) as another sensible one.
Sure, that's another possible semantics.
Should I implement that instead?
> A
> change in meaning may then also result in the three option combinations
> above possibly not all doing the same.
>
> As an aside: As you update the patch, please try to keep the title in
> line with what the patch actually does.
>
I'm assuming you mean the email title (the patch title looks ok to me),
and I've updated it.
> Also, ftaod, I don't mean to stand in the way of another maintainer
> approving any of the forms proposed so far. This specifically also
> includes the use of '+' as a separator, which I personally don't
> (currently) intend to approve.
Well, in case that's blocking you from giving approval, I've updated the
patch to use the ',' separator.
Thanks,
- Tom
Comments
On 27.02.2023 12:43, Tom de Vries wrote:
> On 2/27/23 10:03, Jan Beulich wrote:
>> But I guess whether that's really
>> needed first of all depends on the semantics we want e.g.
>>
>> --nocompress-debug-sections --compress-debug-sections=force
>>
>> to have (which, with how you have it presently, could also be expressed
>> as
>>
>> --compress-debug-sections=none+force
>>
>> or
>>
>> --compress-debug-sections=none --compress-debug-sections=force
>>
>> afaict). I view the present meaning as one sensible one, but I could
>> also see "none" (or equivalent) simply zapping the compression type
>> (and hence rendering "force" meaningless) as another sensible one.
>
> Sure, that's another possible semantics.
>
> Should I implement that instead?
Not sure - as said, depends on what exactly is wanted. I find both
variants leaving too much room for ambiguity, so I can't really decide
(for myself).
>> A
>> change in meaning may then also result in the three option combinations
>> above possibly not all doing the same.
>>
>
>> As an aside: As you update the patch, please try to keep the title in
>> line with what the patch actually does.
>>
>
> I'm assuming you mean the email title (the patch title looks ok to me),
> and I've updated it.
Hmm, yes, sorry - I'm normally implying new patch versions to be at
the root of new threads (and with increased version number), not in
reply to earlier versions. Hence I didn't pay attention to the Re: ...
still being there from the initial patch.
Jan
From 0fb4ed6d648a69799cdbf6b19fd36c6125c5fc41 Mon Sep 17 00:00:00 2001
From: Tom de Vries <tdevries@suse.de>
Date: Thu, 23 Feb 2023 12:53:40 +0100
Subject: [PATCH] gas: Add --compress-debug-sections=force
Gas has an option --compress-debug-sections that allows it to generate
compressed debug sections.
That does not guarantee that the debug sections are in fact compressed:
...
$ gcc hello.c -Wa,-gdwarf-5 -c -Wa,--compress-debug-sections=zstd
$ readelf -S -W hello.o | grep " .debug"
[ 9] .debug_line PROGBITS 0000a8 000053 00 0 0 1
[11] .debug_line_str PROGBITS 0000fb 000025 01 MS 0 0 1
[12] .debug_info PROGBITS 000120 000039 00 0 0 1
[14] .debug_abbrev PROGBITS 000159 000028 00 0 0 1
[15] .debug_aranges PROGBITS 000190 000030 00 0 0 16
[17] .debug_str PROGBITS 0001c0 000039 01 MS 0 0 1
...
Sensibly so, they're only compressed if that provides a size benefit.
However, for the purpose of testing components consuming dwarf
we may want the sections to be compressed regardless.
Add a new suboption --compress-debug-sections=force that ignores the size
heuristic, such that we have instead:
...
$ gcc hello.c -Wa,-gdwarf-5 -c -Xassembler \
--compress-debug-sections=zstd,force
$ readelf -S -W hello.o | grep " .debug"
[ 9] .debug_line PROGBITS 0000a8 000064 00 C 0 0 8
[11] .debug_line_str PROGBITS 000110 000046 01 MSC 0 0 8
[12] .debug_info PROGBITS 000158 000046 00 C 0 0 8
[14] .debug_abbrev PROGBITS 0001a0 000049 00 C 0 0 8
[15] .debug_aranges PROGBITS 0001f0 000034 00 C 0 0 8
[17] .debug_str PROGBITS 000228 00005a 01 MSC 0 0 8
...
Advertised as:
...
$ as --help
...
--compress-debug-sections[={none|<format>|force|force,<format>}]
where <format> is {zlib|zlib-gnu|zlib-gabi|zstd}
compress DWARF debug sections
Default: zstd
...
Tested on x86_64-linux.
---
gas/as.c | 106 +++++++++++++++++++++++++++++++++++++++---------
gas/as.h | 10 +++++
gas/doc/as.texi | 10 ++++-
gas/write.c | 5 ++-
4 files changed, 108 insertions(+), 23 deletions(-)
@@ -230,6 +230,8 @@ enum compressed_debug_section_type flag_compress_debug
= DEFAULT_COMPRESSED_DEBUG_ALGORITHM;
#endif
+enum compress_debug_action compress_debug_action = cda_default;
+
static void
show_usage (FILE * stream)
{
@@ -252,7 +254,8 @@ Options:\n\
fprintf (stream, _("\
--alternate initially turn on alternate macro syntax\n"));
fprintf (stream, _("\
- --compress-debug-sections[={none|zlib|zlib-gnu|zlib-gabi|zstd}]\n\
+ --compress-debug-sections[={none|<format>|force|force,<format>}]\n\
+ where <format> is {zlib|zlib-gnu|zlib-gabi|zstd}\n\
compress DWARF debug sections\n")),
fprintf (stream, _("\
Default: %s\n"),
@@ -418,6 +421,84 @@ Options:\n\
fprintf (stream, _("Report bugs to %s\n"), REPORT_BUGS_TO);
}
+static void
+parse_compress_debug_optarg_1 (const char *optarg)
+{
+ gas_assert (optarg != NULL);
+
+ if (strcmp (optarg, "force") == 0)
+ {
+ compress_debug_action = cda_force;
+ return;
+ }
+
+ enum compressed_debug_section_type tmp
+ = bfd_get_compression_algorithm (optarg);
+
+#ifndef HAVE_ZSTD
+ if (tmp == COMPRESS_DEBUG_ZSTD)
+ as_fatal (_ ("--compress-debug-sections=zstd: gas is not "
+ "built with zstd support"));
+#endif
+
+ if (tmp == COMPRESS_UNKNOWN)
+ as_fatal (_("Invalid --compress-debug-sections option: `%s'"),
+ optarg);
+
+ if (tmp == COMPRESS_DEBUG_NONE)
+ {
+ compress_debug_action = cda_none;
+ return;
+ }
+
+ compress_debug_action = cda_yes;
+ flag_compress_debug = tmp;
+}
+
+static void
+parse_compress_debug_optarg (const char *optarg)
+{
+#if !defined OBJ_ELF && !defined OBJ_MAYBE_ELF
+ as_fatal (_("--compress-debug-sections=%s is unsupported"),
+ optarg);
+#endif
+
+ /* Tokenize subopts pass to parse_compress_debug_optarg_1. */
+ char sep = ',';
+ while (true)
+ {
+ const char *idx = optarg;
+ while (*idx != '\0' && *idx != sep)
+ idx++;
+
+ size_t len = idx - optarg;
+ if (len == 0)
+ {
+ /* Generate error. */
+ parse_compress_debug_optarg_1 ("");
+ break;
+ }
+
+ char *tmp = xstrndup (optarg, len);
+ parse_compress_debug_optarg_1 (tmp);
+ free (tmp);
+
+ if (*idx == '\0')
+ break;
+
+ /* Step over separator and continue tokenizing. */
+ gas_assert (*idx == sep);
+ optarg = idx + 1;
+ }
+}
+
+static void
+finalize_parse_compress_debug_optarg (void)
+{
+ if (compress_debug_action == cda_none)
+ flag_compress_debug = COMPRESS_DEBUG_NONE;
+}
+
/* Since it is easy to do here we interpret the special arg "-"
to mean "use stdin" and we set that argv[] pointing to "".
After we have munged argv[], the only things left are source file
@@ -747,28 +828,13 @@ This program has absolutely no warranty.\n"));
case OPTION_COMPRESS_DEBUG:
if (optarg)
- {
-#if defined OBJ_ELF || defined OBJ_MAYBE_ELF
- flag_compress_debug = bfd_get_compression_algorithm (optarg);
-#ifndef HAVE_ZSTD
- if (flag_compress_debug == COMPRESS_DEBUG_ZSTD)
- as_fatal (_ ("--compress-debug-sections=zstd: gas is not "
- "built with zstd support"));
-#endif
- if (flag_compress_debug == COMPRESS_UNKNOWN)
- as_fatal (_("Invalid --compress-debug-sections option: `%s'"),
- optarg);
-#else
- as_fatal (_("--compress-debug-sections=%s is unsupported"),
- optarg);
-#endif
- }
+ parse_compress_debug_optarg (optarg);
else
- flag_compress_debug = COMPRESS_DEBUG_GABI_ZLIB;
+ parse_compress_debug_optarg ("zlib-gabi");
break;
case OPTION_NOCOMPRESS_DEBUG:
- flag_compress_debug = COMPRESS_DEBUG_NONE;
+ parse_compress_debug_optarg ("none");
break;
case OPTION_DEBUG_PREFIX_MAP:
@@ -1136,6 +1202,8 @@ This program has absolutely no warranty.\n"));
*pargc = new_argc;
*pargv = new_argv;
+ finalize_parse_compress_debug_optarg ();
+
#ifdef md_after_parse_args
md_after_parse_args ();
#endif
@@ -331,6 +331,16 @@ COMMON int flag_traditional_format;
/* Type of compressed debug sections we should generate. */
COMMON enum compressed_debug_section_type flag_compress_debug;
+/* Whether we should compress debug sections. */
+enum compress_debug_action
+{
+ cda_default,
+ cda_none,
+ cda_force,
+ cda_yes,
+};
+COMMON enum compress_debug_action compress_debug_action;
+
/* TRUE if .note.GNU-stack section with SEC_CODE should be created */
COMMON int flag_execstack;
@@ -718,7 +718,8 @@ Begin in alternate macro mode.
Compress DWARF debug sections using zlib with SHF_COMPRESSED from the
ELF ABI. The resulting object file may not be compatible with older
linkers and object file utilities. Note if compression would make a
-given section @emph{larger} then it is not compressed.
+given section @emph{larger} then it is not compressed, unless
+@option{--compress-debug-section=force} is used.
@ifset ELF
@cindex @samp{--compress-debug-sections=} option
@@ -727,6 +728,7 @@ given section @emph{larger} then it is not compressed.
@itemx --compress-debug-sections=zlib-gnu
@itemx --compress-debug-sections=zlib-gabi
@itemx --compress-debug-sections=zstd
+@itemx --compress-debug-sections=force
These options control how DWARF debug sections are compressed.
@option{--compress-debug-sections=none} is equivalent to
@option{--nocompress-debug-sections}.
@@ -738,7 +740,11 @@ using the obsoleted zlib-gnu format. The debug sections are renamed to begin
with @samp{.zdebug}.
@option{--compress-debug-sections=zstd} compresses DWARF debug
sections using zstd. Note - if compression would actually make a section
-@emph{larger}, then it is not compressed nor renamed.
+@emph{larger}, then it is not compressed nor renamed, unless
+@option{--compress-debug-section=force} is used.
+@option{--compress-debug-sections=force} compresses DWARF debug sections,
+even if this does not reduce size. It can be used in conjunction with a format
+selection, for instance @option{--compress-debug-section=zstd,force}.
@end ifset
@@ -1463,9 +1463,10 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
segment_info_type *seginfo = seg_info (sec);
bfd_size_type uncompressed_size = sec->size;
flagword flags = bfd_section_flags (sec);
+ bool force_compress_debug = compress_debug_action == cda_force;
if (seginfo == NULL
- || uncompressed_size < 32
+ || (!force_compress_debug && uncompressed_size < 32)
|| (flags & SEC_HAS_CONTENTS) == 0)
return;
@@ -1582,7 +1583,7 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
/* PR binutils/18087: If compression didn't make the section smaller,
just keep it uncompressed. */
- if (compressed_size >= uncompressed_size)
+ if (!force_compress_debug && compressed_size >= uncompressed_size)
return;
/* Replace the uncompressed frag list with the compressed frag list. */
--
2.35.3