[patch] Add --compress-debug-sections option to gas
Cary Coutant
ccoutant@google.com
Mon Jun 28 21:39:00 GMT 2010
A couple of years ago, Craig Silverstein submitted a patch to add
support for compressed debug sections generated by the linker:
http://sourceware.org/ml/binutils/2008-06/msg00203.html
The attached patch extends this support to the assembler, adding a new
--compress-debug-sections option to gas, and adding the necessary
support (and fixing a couple of bugs in the original patch) for
reading compressed sections in relocatables to bfd, objdump, and
readelf.
Tested on x86_64 by compiling with and without
-Wa,--compress-debug-sections, and comparing readelf -w output and
objdump -W output. No regressions in the test suite.
A patch for gold to read files with compressed debug sections is in progress.
I have to admit that I'm not happy with a couple of things:
(1) In both bfd/dwarf2.c and binutils/objdump.c, in order to
uncompress the section before relocating it, I call
bfd_get_section_contents() to get the unrelocated section contents,
then decompress the contents and put a pointer to the decompressed
contents in sec->contents, setting the SEC_IN_MEMORY flag so that
bfd_simple_get_relocated_section_contents() would not go read the
section again. I couldn't find a simpler way to apply relocations
after decompression.
(2) In gas/write.c, I used a similar trick to signal write_contents()
that the frags had already been collected and compressed. An
alternative I considered was to simply replace the frag list with a
single frag containing the entire compressed section contents, but
that seemed a bit more complicated.
Advice on these issues is welcome.
-cary
p.s. I'm not sure why my regenerated libbfd.h is different from the
original -- nothing changed except for parameters to
bfd_generic_get_relocated_section_contents() that used to be unnamed.
Did "make headers" change behavior since the last time that file was
regenerated? Should I just leave this out of the patch?
bfd/ChangeLog:
* bfd-in2.h: Regenerate.
* compress.c (bfd_compress_section_contents): New function.
* dwarf2.c (read_and_uncompress_section): New function.
(read_section): Call it.
(find_line): Likewise.
* libbfd.h: Regenerate.
binutils/ChangeLog:
* objdump.c (load_specific_debug_section): Decompress section contents
before applying relocations.
* readelf.c (load_specific_debug_section): Update section size after
decompression.
gas/ChangeLog:
* as.c (parse_args): Add --compress-debug-sections and
--nocompress-debug-sections.
* as.h (flag_compress_debug): New variable.
* write.c (compress_debug): New function.
(write_contents): Check for uncompressed section.
(write_object_file): Compress debug sections if requested.
-------------- next part --------------
diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 5c42128..bd648ce 100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -5821,6 +5821,9 @@ bfd_byte *bfd_simple_get_relocated_section_contents
bfd_boolean bfd_uncompress_section_contents
(bfd_byte **buffer, bfd_size_type *size);
+bfd_boolean bfd_compress_section_contents
+ (bfd_byte **buffer, bfd_size_type *size);
+
#ifdef __cplusplus
}
#endif
diff --git a/bfd/compress.c b/bfd/compress.c
index 5b6ee0e..7b334a0 100644
--- a/bfd/compress.c
+++ b/bfd/compress.c
@@ -1,4 +1,4 @@
-/* ELF attributes support (based on ARM EABI attributes).
+/* Compressed section support (intended for debug sections).
Copyright 2008
Free Software Foundation, Inc.
@@ -120,3 +120,73 @@ bfd_uncompress_section_contents (bfd_byte **buffer, bfd_size_type *size)
return FALSE;
#endif /* HAVE_ZLIB_H */
}
+
+/*
+FUNCTION
+ bfd_compress_section_contents
+
+SYNOPSIS
+ bfd_boolean bfd_compress_section_contents
+ (bfd_byte **buffer, bfd_size_type *size);
+
+DESCRIPTION
+
+ Compresses a section using zlib, in place. At the call to this
+ function, *@var{buffer} and *@var{size} should point to the section
+ contents to be compressed. At the end of the function, *@var{buffer}
+ and *@var{size} will point to the compressed contents. This function
+ assumes *BUFFER was allocated using bfd_malloc() or equivalent. If
+ zlib is not installed on this machine, the input is unmodified.
+
+ Returns @code{FALSE} if unable to compress successfully; in that case
+ the input is unmodified. Otherwise, returns @code{TRUE}.
+*/
+
+bfd_boolean
+bfd_compress_section_contents (bfd_byte **buffer, bfd_size_type *size)
+{
+#ifndef HAVE_ZLIB_H
+ /* These are just to quiet gcc. */
+ buffer = 0;
+ size = 0;
+ return FALSE;
+#else
+ bfd_size_type uncompressed_size = *size;
+ bfd_byte *uncompressed_buffer = *buffer;
+ bfd_size_type compressed_size;
+ bfd_byte *compressed_buffer;
+ int rc;
+ bfd_size_type header_size = 12;
+
+ compressed_size = compressBound (uncompressed_size) + header_size;
+ compressed_buffer = (bfd_byte *) bfd_malloc (compressed_size);
+
+ rc = compress ((Bytef*) compressed_buffer + header_size,
+ &compressed_size,
+ (const Bytef*) uncompressed_buffer,
+ uncompressed_size);
+ if (rc != Z_OK)
+ {
+ free (compressed_buffer);
+ return FALSE;
+ }
+
+ /* Write the zlib header. In this case, it should be "ZLIB" followed
+ by the uncompressed section size, 8 bytes in big-endian order. */
+ memcpy (compressed_buffer, "ZLIB", 4);
+ compressed_buffer[4] = uncompressed_size >> 56;
+ compressed_buffer[5] = uncompressed_size >> 48;
+ compressed_buffer[6] = uncompressed_size >> 40;
+ compressed_buffer[7] = uncompressed_size >> 32;
+ compressed_buffer[8] = uncompressed_size >> 24;
+ compressed_buffer[9] = uncompressed_size >> 16;
+ compressed_buffer[10] = uncompressed_size >> 8;
+ compressed_buffer[11] = uncompressed_size;
+ compressed_size += header_size;
+
+ free (uncompressed_buffer);
+ *buffer = compressed_buffer;
+ *size = compressed_size;
+ return TRUE;
+#endif /* HAVE_ZLIB_H */
+}
diff --git a/bfd/dwarf2.c b/bfd/dwarf2.c
index 9b194aa..ffe1108 100644
--- a/bfd/dwarf2.c
+++ b/bfd/dwarf2.c
@@ -405,6 +405,54 @@ lookup_info_hash_table (struct info_hash_table *hash_table, const char *key)
return entry ? entry->head : NULL;
}
+/* Read a section, uncompress it if necessary, and relocate it. */
+
+static bfd_boolean
+read_and_uncompress_section (bfd * abfd,
+ asection * msec,
+ bfd_boolean section_is_compressed,
+ asymbol ** syms,
+ bfd_byte ** section_buffer,
+ bfd_size_type * section_size)
+{
+ /* Get the unrelocated contents of the section. */
+ *section_buffer = (bfd_byte *) bfd_malloc (*section_size);
+ if (! *section_buffer)
+ return FALSE;
+ if (! bfd_get_section_contents (abfd, msec, *section_buffer,
+ 0, *section_size))
+ return FALSE;
+
+ if (section_is_compressed)
+ {
+ if (! bfd_uncompress_section_contents (section_buffer, section_size))
+ {
+ (*_bfd_error_handler) (_("Dwarf Error: unable to decompress %s section."),
+ bfd_get_section_name (abfd, msec));
+ bfd_set_error (bfd_error_bad_value);
+ return FALSE;
+ }
+ }
+
+ if (syms)
+ {
+ /* We want to relocate the data we've already read (and
+ decompressed), so we store a pointer to the data in
+ the bfd_section, and tell it that the contents are
+ already in memory. */
+ BFD_ASSERT (msec->contents == NULL && (msec->flags & SEC_IN_MEMORY) == 0);
+ msec->contents = *section_buffer;
+ msec->flags |= SEC_IN_MEMORY;
+ msec->size = *section_size;
+ *section_buffer
+ = bfd_simple_get_relocated_section_contents (abfd, msec, NULL, syms);
+ if (! *section_buffer)
+ return FALSE;
+ }
+
+ return TRUE;
+}
+
/* Read a section into its appropriate place in the dwarf2_debug
struct (indicated by SECTION_BUFFER and SECTION_SIZE). If SYMS is
not NULL, use bfd_simple_get_relocated_section_contents to read the
@@ -440,32 +488,10 @@ read_section (bfd * abfd,
}
*section_size = msec->rawsize ? msec->rawsize : msec->size;
- if (syms)
- {
- *section_buffer
- = bfd_simple_get_relocated_section_contents (abfd, msec, NULL, syms);
- if (! *section_buffer)
- return FALSE;
- }
- else
- {
- *section_buffer = (bfd_byte *) bfd_malloc (*section_size);
- if (! *section_buffer)
- return FALSE;
- if (! bfd_get_section_contents (abfd, msec, *section_buffer,
- 0, *section_size))
- return FALSE;
- }
- if (section_is_compressed)
- {
- if (! bfd_uncompress_section_contents (section_buffer, section_size))
- {
- (*_bfd_error_handler) (_("Dwarf Error: unable to decompress %s section."), compressed_section_name);
- bfd_set_error (bfd_error_bad_value);
- return FALSE;
- }
- }
+ if (! read_and_uncompress_section (abfd, msec, section_is_compressed,
+ syms, section_buffer, section_size))
+ return FALSE;
}
/* It is possible to get a bad value for the offset into the section
@@ -3242,23 +3268,17 @@ find_line (bfd *abfd,
{
bfd_size_type size = msec->size;
bfd_byte *buffer, *tmp;
+ bfd_boolean is_compressed =
+ strcmp (msec->name, DWARF2_COMPRESSED_DEBUG_INFO) == 0;
if (size == 0)
continue;
- buffer = (bfd_simple_get_relocated_section_contents
- (debug_bfd, msec, NULL, symbols));
- if (! buffer)
+ if (! read_and_uncompress_section (debug_bfd, msec,
+ is_compressed, symbols,
+ &buffer, &size))
goto done;
- if (strcmp (msec->name, DWARF2_COMPRESSED_DEBUG_INFO) == 0)
- {
- if (! bfd_uncompress_section_contents (&buffer, &size))
- {
- free (buffer);
- goto done;
- }
- }
tmp = (bfd_byte *) bfd_realloc (stash->info_ptr_memory,
total_size + size);
if (tmp == NULL)
diff --git a/bfd/libbfd.h b/bfd/libbfd.h
index 233891c..3da79d9 100644
--- a/bfd/libbfd.h
+++ b/bfd/libbfd.h
@@ -2243,12 +2243,12 @@ bfd_boolean bfd_generic_merge_sections
(bfd *, struct bfd_link_info *);
bfd_byte *bfd_generic_get_relocated_section_contents
- (bfd *,
- struct bfd_link_info *,
- struct bfd_link_order *,
- bfd_byte *,
- bfd_boolean,
- asymbol **);
+ (bfd *abfd,
+ struct bfd_link_info *link_info,
+ struct bfd_link_order *link_order,
+ bfd_byte *data,
+ bfd_boolean relocatable,
+ asymbol **symbols);
/* Extracted from archures.c. */
extern const bfd_arch_info_type bfd_default_arch_struct;
diff --git a/binutils/objdump.c b/binutils/objdump.c
index 2a419b7..f94dee9 100644
--- a/binutils/objdump.c
+++ b/binutils/objdump.c
@@ -2205,14 +2205,8 @@ load_specific_debug_section (enum dwarf_section_display_enum debug,
section->size = bfd_get_section_size (sec);
section->start = (unsigned char *) xmalloc (section->size);
- if (is_relocatable && debug_displays [debug].relocate)
- ret = bfd_simple_get_relocated_section_contents (abfd,
- sec,
- section->start,
- syms) != NULL;
- else
- ret = bfd_get_section_contents (abfd, sec, section->start, 0,
- section->size);
+ ret = bfd_get_section_contents (abfd, sec, section->start, 0,
+ section->size);
if (! ret)
{
@@ -2234,6 +2228,30 @@ load_specific_debug_section (enum dwarf_section_display_enum debug,
section->size = size;
}
+ if (is_relocatable && debug_displays [debug].relocate)
+ {
+ /* We want to relocate the data we've already read (and
+ decompressed), so we store a pointer to the data in
+ the bfd_section, and tell it that the contents are
+ already in memory. */
+ sec->contents = section->start;
+ sec->flags |= SEC_IN_MEMORY;
+ sec->size = section->size;
+
+ ret = bfd_simple_get_relocated_section_contents (abfd,
+ sec,
+ section->start,
+ syms) != NULL;
+
+ if (! ret)
+ {
+ free_debug_section (debug);
+ printf (_("\nCan't get contents for section '%s'.\n"),
+ section->name);
+ return 0;
+ }
+ }
+
return 1;
}
diff --git a/binutils/readelf.c b/binutils/readelf.c
index d4f47ca..1c3cb8b 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -9962,8 +9962,11 @@ load_specific_debug_section (enum dwarf_section_display_enum debug,
return 0;
if (section_is_compressed)
- if (! uncompress_section_contents (§ion->start, §ion->size))
- return 0;
+ {
+ if (! uncompress_section_contents (§ion->start, §ion->size))
+ return 0;
+ sec->sh_size = section->size;
+ }
if (debug_displays [debug].relocate)
apply_relocations ((FILE *) file, sec, section->start);
diff --git a/gas/as.c b/gas/as.c
index d617b33..e494fa5 100644
--- a/gas/as.c
+++ b/gas/as.c
@@ -437,7 +437,9 @@ parse_args (int * pargc, char *** pargv)
OPTION_AL,
OPTION_HASH_TABLE_SIZE,
OPTION_REDUCE_MEMORY_OVERHEADS,
- OPTION_WARN_FATAL
+ OPTION_WARN_FATAL,
+ OPTION_COMPRESS_DEBUG,
+ OPTION_NOCOMPRESS_DEBUG
/* When you add options here, check that they do
not collide with OPTION_MD_BASE. See as.h. */
};
@@ -455,6 +457,8 @@ parse_args (int * pargc, char *** pargv)
,{"a", optional_argument, NULL, 'a'}
/* Handle -al=<FILE>. */
,{"al", optional_argument, NULL, OPTION_AL}
+ ,{"compress-debug-sections", no_argument, NULL, OPTION_COMPRESS_DEBUG}
+ ,{"nocompress-debug-sections", no_argument, NULL, OPTION_NOCOMPRESS_DEBUG}
,{"debug-prefix-map", required_argument, NULL, OPTION_DEBUG_PREFIX_MAP}
,{"defsym", required_argument, NULL, OPTION_DEFSYM}
,{"dump-config", no_argument, NULL, OPTION_DUMPCONFIG}
@@ -634,6 +638,14 @@ This program has absolutely no warranty.\n"));
#endif
exit (EXIT_SUCCESS);
+ case OPTION_COMPRESS_DEBUG:
+ flag_compress_debug = 1;
+ break;
+
+ case OPTION_NOCOMPRESS_DEBUG:
+ flag_compress_debug = 0;
+ break;
+
case OPTION_DEBUG_PREFIX_MAP:
add_debug_prefix_map (optarg);
break;
diff --git a/gas/as.h b/gas/as.h
index 2b2562e..7c16382 100644
--- a/gas/as.h
+++ b/gas/as.h
@@ -365,6 +365,9 @@ COMMON int flag_strip_local_absolute;
/* True if we should generate a traditional format object file. */
COMMON int flag_traditional_format;
+/* TRUE if debug sections should be compressed. */
+COMMON int flag_compress_debug;
+
/* TRUE if .note.GNU-stack section with SEC_CODE should be created */
COMMON int flag_execstack;
diff --git a/gas/write.c b/gas/write.c
index a148b24..4fc27fc 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -1289,6 +1289,77 @@ write_relocs (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
}
static void
+compress_debug (bfd *abfd ATTRIBUTE_UNUSED,
+ asection *sec,
+ void *xxx ATTRIBUTE_UNUSED)
+{
+ segment_info_type *seginfo = seg_info (sec);
+ addressT offset = 0;
+ fragS *f;
+ bfd_size_type section_size = (bfd_size_type) sec->size;
+ bfd_byte *contents;
+ const char *section_name;
+ char *compressed_name;
+ int x;
+
+ if (seginfo == NULL
+ || !(bfd_get_section_flags (abfd, sec) & SEC_HAS_CONTENTS)
+ || (bfd_get_section_flags (abfd, sec) & SEC_ALLOC))
+ return;
+
+ section_name = bfd_get_section_name (stdoutput, sec);
+ if (strncmp (section_name, ".debug_", 7) != 0)
+ return;
+
+ /* Gather the frags into a contiguous buffer. */
+ contents = (bfd_byte *) xmalloc (section_size);
+ for (f = seginfo->frchainP->frch_root;
+ f;
+ f = f->fr_next)
+ {
+ addressT fill_size;
+ char *fill_literal;
+ offsetT count;
+
+ gas_assert (f->fr_type == rs_fill);
+ if (f->fr_fix)
+ {
+ memcpy (contents + offset, f->fr_literal, (size_t) f->fr_fix);
+ offset += f->fr_fix;
+ }
+ fill_literal = f->fr_literal + f->fr_fix;
+ fill_size = f->fr_var;
+ count = f->fr_offset;
+ gas_assert (count >= 0);
+ if (fill_size && count)
+ {
+ while (count--)
+ {
+ memcpy (contents + offset, fill_literal, (size_t) fill_size);
+ offset += fill_size;
+ }
+ }
+ }
+
+ /* Compress the buffer. */
+ if (!bfd_compress_section_contents (&contents, §ion_size))
+ return;
+
+ /* Store the compressed contents in the section. */
+ sec->contents = contents;
+ sec->flags |= SEC_IN_MEMORY;
+ x = bfd_set_section_size (abfd, sec, section_size);
+ gas_assert (x);
+
+ /* Change the section name. */
+ compressed_name = (char *) xmalloc (strlen (section_name) + 2);
+ compressed_name[0] = '.';
+ compressed_name[1] = 'z';
+ strcpy (compressed_name + 2, section_name + 1);
+ bfd_section_name (stdoutput, sec) = compressed_name;
+}
+
+static void
write_contents (bfd *abfd ATTRIBUTE_UNUSED,
asection *sec,
void *xxx ATTRIBUTE_UNUSED)
@@ -1297,6 +1368,20 @@ write_contents (bfd *abfd ATTRIBUTE_UNUSED,
addressT offset = 0;
fragS *f;
+ if (bfd_get_section_flags (abfd, sec) & SEC_IN_MEMORY)
+ {
+ /* We already gathered the frags and compressed the data. */
+ int x;
+
+ x = bfd_set_section_contents (stdoutput, sec, sec->contents,
+ (file_ptr) offset,
+ (bfd_size_type) sec->size);
+ if (!x)
+ as_fatal (_("can't write %s: %s"), stdoutput->filename,
+ bfd_errmsg (bfd_get_error ()));
+ return;
+ }
+
/* Write out the frags. */
if (seginfo == NULL
|| !(bfd_get_section_flags (abfd, sec) & SEC_HAS_CONTENTS))
@@ -1912,6 +1997,13 @@ write_object_file (void)
obj_frob_file_after_relocs ();
#endif
+ /* Once all relocations have been written, we can compress the
+ contents of the debug sections. This needs to be done before
+ we start writing any sections, because it will affect the file
+ layout, which is fixed once we start writing contents. */
+ if (flag_compress_debug)
+ bfd_map_over_sections (stdoutput, compress_debug, (char *) 0);
+
bfd_map_over_sections (stdoutput, write_contents, (char *) 0);
}
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