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eu-strip --reloc-debug-sections
- From: Mark Wielaard <mjw at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Mon, 23 May 2011 22:04:38 +0200
- Subject: eu-strip --reloc-debug-sections
Hi,
The following patch adds a new option to eu-strip.
2011-05-23 Mark Wielaard <mjw@redhat.com>
* strip.c (OPT_RELOC_DEBUG): New option.
(argp_option): Add new --reloc-debug-sections option.
(main): Check new option.
(parse_opt): Likewise.
(handle_elf): Remove any relocations between debug sections
in ET_REL for the debug file when requested.
eu-strip --reloc-debug-sections is mostly for the separate debuginfo
kernel modules. Which are ET_REL files. So they have relocation
sections. These take up a lot of space for the debug sections. Which
isn't really necessary since those sections are not allocated and will
not be relinked. So you can use eu-strip --reloc-debug-sections in
combination with -f to create a separate .debug file that has all
(simple absolute) cross debug section relocations resolved.
Rebuilding kernel-debuginfo-2.6.35.13-91.fc14.x86_64 showed a nice
reduction in size.
Before: Compressed: 238 M Expanded: 1381 M
After : Compressed: 207 M Expanded: 908 M
On the mjw/reloc-debug-sections branch there are also a couple of
testcases, which make sure there is no difference in readelf -w output
with/without --reloc-debug-sections:
2011-05-23 Mark Wielaard <mjw@redhat.com>
* Makefile.am (TESTS): Add run-strip-reloc.sh.
(EXTRA_DIST): Add run-strip-reloc.sh, hello_i386.ko.bz2
hello_x86_64.ko.bz2 and hello_ppc64.ko.bz2
* run-strip-reloc.sh: New test.
* hello_i386.ko.bz2: New test file.
* hello_x86_64.ko.bz2: Likewise.
* hello_ppc64.ko.bz2: Likewise.
Also tested against the above rebuild kernel package with systemtap make
installcheck, which showed no difference in failures.
Please let me know about any comments on the patch before I push it.
Thanks,
Mark
commit 1662bc3880ae5acae6aa2a3013d193223c36f189
Author: Mark Wielaard <mjw@redhat.com>
Date: Mon May 16 11:33:11 2011 +0200
strip: Add --reloc-debug-sections option.
diff --git a/src/strip.c b/src/strip.c
index 8c3c57d..f680061 100644
--- a/src/strip.c
+++ b/src/strip.c
@@ -53,6 +53,7 @@
#include <libebl.h>
#include <system.h>
+typedef uint8_t GElf_Byte;
/* Name and version of program. */
static void print_version (FILE *stream, struct argp_state *state);
@@ -66,6 +67,7 @@ ARGP_PROGRAM_BUG_ADDRESS_DEF = PACKAGE_BUGREPORT;
#define OPT_REMOVE_COMMENT 0x100
#define OPT_PERMISSIVE 0x101
#define OPT_STRIP_SECTIONS 0x102
+#define OPT_RELOC_DEBUG 0x103
/* Definitions of arguments for argp functions. */
@@ -85,6 +87,8 @@ static const struct argp_option options[] =
N_("Remove section headers (not recommended)"), 0 },
{ "preserve-dates", 'p', NULL, 0,
N_("Copy modified/access timestamps to the output"), 0 },
+ { "reloc-debug-sections", OPT_RELOC_DEBUG, NULL, 0,
+ N_("Resolve all trivial relocations between debug sections if the removed sections are placed in a debug file (only relevant for ET_REL files, operation is not reversable, needs -f)"), 0 },
{ "remove-comment", OPT_REMOVE_COMMENT, NULL, 0,
N_("Remove .comment section"), 0 },
{ "remove-section", 'R', "SECTION", OPTION_HIDDEN, NULL, 0 },
@@ -149,6 +153,9 @@ static bool remove_shdrs;
/* If true relax some ELF rules for input files. */
static bool permissive;
+/* If true perform relocations between debug sections. */
+static bool reloc_debug;
+
int
main (int argc, char *argv[])
@@ -177,6 +184,10 @@ main (int argc, char *argv[])
if (argp_parse (&argp, argc, argv, 0, &remaining, NULL) != 0)
return EXIT_FAILURE;
+ if (reloc_debug && debug_fname == NULL)
+ error (EXIT_FAILURE, 0,
+ gettext ("--reloc-debug-sections used without -f"));
+
/* Tell the library which version we are expecting. */
elf_version (EV_CURRENT);
@@ -253,6 +264,10 @@ parse_opt (int key, char *arg, struct argp_state *state)
preserve_dates = true;
break;
+ case OPT_RELOC_DEBUG:
+ reloc_debug = true;
+ break;
+
case OPT_REMOVE_COMMENT:
remove_comment = true;
break;
@@ -447,10 +462,12 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
int debug_fd = -1;
- /* Get the EBL handling. The -g option is currently the only reason
+ /* Get the EBL handling. Removing all debugging symbols with the -g
+ option or resolving all relocations between debug sections with
+ the --reloc-debug-sections option are currently the only reasons
we need EBL so don't open the backend unless necessary. */
Ebl *ebl = NULL;
- if (remove_debug)
+ if (remove_debug || reloc_debug)
{
ebl = ebl_openbackend (elf);
if (ebl == NULL)
@@ -1609,6 +1626,200 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
}
}
+ /* Remove any relocations between debug sections in ET_REL
+ for the debug file when requested. These relocations are always
+ zero based between the unallocated sections. */
+ if (debug_fname != NULL && reloc_debug && ehdr->e_type == ET_REL)
+ {
+ scn = NULL;
+ cnt = 0;
+ while ((scn = elf_nextscn (debugelf, scn)) != NULL)
+ {
+ cnt++;
+ /* We need the actual section and header from the debugelf
+ not just the cached original in shdr_info because we
+ might want to change the size. */
+ GElf_Shdr shdr_mem;
+ GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
+ if (shdr->sh_type == SHT_REL || shdr->sh_type == SHT_RELA)
+ {
+ /* Make sure that this relocation section points to a
+ section to relocate with contents, that isn't
+ allocated and that is a debug section. */
+ Elf_Scn *tscn = elf_getscn (debugelf, shdr->sh_info);
+ GElf_Shdr tshdr_mem;
+ GElf_Shdr *tshdr = gelf_getshdr (tscn, &tshdr_mem);
+ if (tshdr->sh_type == SHT_NOBITS
+ || tshdr->sh_size == 0
+ || (tshdr->sh_flags & SHF_ALLOC) != 0)
+ continue;
+
+ const char *tname = elf_strptr (debugelf, shstrndx,
+ tshdr->sh_name);
+ if (! tname || ! ebl_debugscn_p (ebl, tname))
+ continue;
+
+ /* OK, lets relocate all trivial cross debug section
+ relocations. */
+ Elf_Data *reldata = elf_getdata (scn, NULL);
+ /* We actually wanted the rawdata, but since we already
+ accessed it earlier as elf_getdata () that won't
+ work. But debug sections are all ELF_T_BYTE, so it
+ doesn't really matter. */
+ Elf_Data *tdata = elf_getdata (tscn, NULL);
+ if (tdata->d_type != ELF_T_BYTE)
+ INTERNAL_ERROR (fname);
+
+ /* Pick up the symbol table and shndx table to
+ resolve relocation symbol indexes. */
+ Elf64_Word symt = shdr->sh_link;
+ Elf_Data *symdata, *xndxdata;
+ symdata = (shdr_info[symt].debug_data
+ ?: shdr_info[symt].data);
+ xndxdata = (shdr_info[shdr_info[symt].symtab_idx].debug_data
+ ?: shdr_info[shdr_info[symt].symtab_idx].data);
+
+ /* Apply one relocation. Returns true when trivial
+ relocation actually done. */
+ bool relocate (GElf_Addr offset, const GElf_Sxword addend,
+ int rtype, int symndx)
+ {
+ /* R_*_NONE relocs can always just be removed. */
+ if (rtype == 0)
+ return true;
+
+ /* We only do simple absolute relocations. */
+ Elf_Type type = ebl_reloc_simple_type (ebl, rtype);
+ if (type == ELF_T_NUM)
+ return false;
+
+ /* These are the types we can relocate. */
+#define TYPES DO_TYPE (BYTE, Byte); DO_TYPE (HALF, Half); \
+ DO_TYPE (WORD, Word); DO_TYPE (SWORD, Sword); \
+ DO_TYPE (XWORD, Xword); DO_TYPE (SXWORD, Sxword)
+
+ /* And only for relocations against other debug sections. */
+ GElf_Sym sym_mem;
+ Elf32_Word xndx;
+ GElf_Sym *sym = gelf_getsymshndx (symdata, xndxdata,
+ symndx, &sym_mem,
+ &xndx);
+ if (GELF_ST_TYPE (sym->st_info) == STT_SECTION)
+ {
+ Elf32_Word sec = (sym->st_shndx == SHN_XINDEX
+ ? xndx : sym->st_shndx);
+ if (ebl_debugscn_p (ebl, shdr_info[sec].name))
+ {
+ size_t size;
+ switch (type)
+ {
+#define DO_TYPE(NAME, Name) \
+ case ELF_T_##NAME: \
+ size = sizeof (GElf_##Name); \
+ break;
+ TYPES;
+#undef DO_TYPE
+ default:
+ return false;
+ }
+
+ if (offset + size > tdata->d_size)
+ error (0, 0, gettext ("bad relocation"));
+
+ /* For SHT_REL sections this is all that needs
+ to be checked. The addend is contained in
+ the original data at the offset already.
+ And the (section) symbol address is zero.
+ So just remove the relocation, it isn't
+ needed anymore. */
+ if (addend == 0)
+ return true;
+
+#define DO_TYPE(NAME, Name) GElf_##Name Name;
+ union { TYPES; } tmpbuf;
+#undef DO_TYPE
+ Elf_Data tmpdata =
+ {
+ .d_type = type,
+ .d_buf = &tmpbuf,
+ .d_size = size,
+ .d_version = EV_CURRENT,
+ };
+ Elf_Data rdata =
+ {
+ .d_type = type,
+ .d_buf = tdata->d_buf + offset,
+ .d_size = size,
+ .d_version = EV_CURRENT,
+ };
+
+ /* For SHT_RELA sections we just take the
+ addend and put it into the relocation slot.
+ The (section) symbol address can be
+ ignored, since it is zero. */
+ switch (type)
+ {
+#define DO_TYPE(NAME, Name) \
+ case ELF_T_##NAME: \
+ tmpbuf.Name = addend; \
+ break;
+ TYPES;
+#undef DO_TYPE
+ default:
+ abort ();
+ }
+
+ Elf_Data *s = gelf_xlatetof (debugelf, &rdata,
+ &tmpdata,
+ ehdr->e_ident[EI_DATA]);
+ if (s == NULL)
+ INTERNAL_ERROR (fname);
+ assert (s == &rdata);
+
+ return true;
+ }
+ }
+ return false;
+ }
+
+ size_t nrels = shdr->sh_size / shdr->sh_entsize;
+ size_t next = 0;
+ if (shdr->sh_type == SHT_REL)
+ for (size_t relidx = 0; relidx < nrels; ++relidx)
+ {
+ GElf_Rel rel_mem;
+ GElf_Rel *r = gelf_getrel (reldata, relidx, &rel_mem);
+ if (! relocate (r->r_offset, 0,
+ GELF_R_TYPE (r->r_info),
+ GELF_R_SYM (r->r_info)))
+ {
+ if (relidx != next)
+ gelf_update_rel (reldata, next, r);
+ ++next;
+ }
+ }
+ else
+ for (size_t relidx = 0; relidx < nrels; ++relidx)
+ {
+ GElf_Rela rela_mem;
+ GElf_Rela *r = gelf_getrela (reldata, relidx, &rela_mem);
+ if (! relocate (r->r_offset, r->r_addend,
+ GELF_R_TYPE (r->r_info),
+ GELF_R_SYM (r->r_info)))
+ {
+ if (relidx != next)
+ gelf_update_rela (reldata, next, r);
+ ++next;
+ }
+ }
+
+ nrels = next;
+ shdr->sh_size = reldata->d_size = nrels * shdr->sh_entsize;
+ gelf_update_shdr (scn, shdr);
+ }
+ }
+ }
+
/* Now that we have done all adjustments to the data,
we can actually write out the debug file. */
if (debug_fname != NULL)