[v2,3/3] gas: Add --compress-debug-sections={heuristic-always, heuristic-sizewin}
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Commit Message
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=heuristic-always that ignores
the size heuristic, such that we have instead:
...
$ gcc hello.c -Wa,-gdwarf-5 -c -Xassembler \
--compress-debug-sections=zstd,heuristic-always
$ 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
...
Also add an option --compress-debug-sections=heuristic-sizewin that represents
the current default.
Advertised as:
...
$ as --help
...
--compress-debug-sections[={none|zlib|zlib-gnu|zlib-gabi|zstd|heuristic-always|heuristic-sizewin}]
compress DWARF debug sections
Default: zlib
...
Tested on x86_64-linux.
---
gas/as.c | 16 +++++++++++++++-
gas/as.h | 8 ++++++++
gas/write.c | 7 +++++--
3 files changed, 28 insertions(+), 3 deletions(-)
@@ -230,6 +230,8 @@ enum compressed_debug_section_type flag_compress_debug
= DEFAULT_COMPRESSED_DEBUG_ALGORITHM;
#endif
+enum compress_debug_heuristic compress_debug_heuristic = cdh_sizewin;
+
static void
show_usage (FILE * stream)
{
@@ -252,7 +254,7 @@ 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|zlib|zlib-gnu|zlib-gabi|zstd|heuristic-sizewin|heuristic-always}]\n\
compress DWARF debug sections\n")),
fprintf (stream, _("\
Default: %s\n"),
@@ -423,6 +425,18 @@ parse_compress_debug_optarg_1 (const char *optarg)
{
gas_assert (optarg != NULL);
+ if (strcmp (optarg, "heuristic-sizewin") == 0)
+ {
+ compress_debug_heuristic = cdh_sizewin;
+ return;
+ }
+
+ if (strcmp (optarg, "heuristic-always") == 0)
+ {
+ compress_debug_heuristic = cdh_always;
+ return;
+ }
+
enum compressed_debug_section_type tmp
= bfd_get_compression_algorithm (optarg);
@@ -331,6 +331,14 @@ COMMON int flag_traditional_format;
/* Type of compressed debug sections we should generate. */
COMMON enum compressed_debug_section_type flag_compress_debug;
+/* Debug sections compression heuristics. */
+enum compress_debug_heuristic
+{
+ cdh_sizewin,
+ cdh_always
+};
+COMMON enum compress_debug_heuristic compress_debug_heuristic;
+
/* TRUE if .note.GNU-stack section with SEC_CODE should be created */
COMMON int flag_execstack;
@@ -1463,9 +1463,11 @@ 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 compress_debug_heuristic_sizewin
+ = compress_debug_heuristic == cdh_sizewin;
if (seginfo == NULL
- || uncompressed_size < 32
+ || (compress_debug_heuristic_sizewin && uncompressed_size < 32)
|| (flags & SEC_HAS_CONTENTS) == 0)
return;
@@ -1582,7 +1584,8 @@ 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 (compress_debug_heuristic_sizewin
+ && compressed_size >= uncompressed_size)
return;
/* Replace the uncompressed frag list with the compressed frag list. */