Author: markj
Date: Sun Feb 24 15:15:50 2013
New Revision: 247221
URL: http://svnweb.freebsd.org/changeset/base/247221
Log:
Merge part of r1712 from elftoolchain, making it possible to resize ELF
sections and indirectly change the layout of an ELF file when
ELF_F_LAYOUT is not set.
PR: bin/167103
Approved by: rstone (co-mentor)
Obtained from: elftoolchain
MFC after: 2 weeks
Modified:
head/lib/libelf/elf_update.c
Modified: head/lib/libelf/elf_update.c
==============================================================================
--- head/lib/libelf/elf_update.c Sun Feb 24 11:32:45 2013
(r247220)
+++ head/lib/libelf/elf_update.c Sun Feb 24 15:15:50 2013
(r247221)
@@ -41,89 +41,79 @@ __FBSDID("$FreeBSD$");
#include "_libelf.h"
/*
- * Update the internal data structures associated with an ELF object.
- * Returns the size in bytes the ELF object would occupy in its file
- * representation.
+ * Layout strategy:
*
- * After a successful call to this function, the following structures
- * are updated:
+ * - Case 1: ELF_F_LAYOUT is asserted
+ * In this case the application has full control over where the
+ * section header table, program header table, and section data
+ * will reside. The library only perform error checks.
*
- * - The ELF header is updated.
- * - All sections are sorted in order of ascending addresses and their
- * section header table entries updated. An error is signalled
- * if an overlap was detected among sections.
- * - All data descriptors associated with a section are sorted in order
- * of ascending addresses. Overlaps, if detected, are signalled as
- * errors. Other sanity checks for alignments, section types etc. are
- * made.
+ * - Case 2: ELF_F_LAYOUT is not asserted
*
- * After a resync_elf() successfully returns, the ELF descriptor is
- * ready for being handed over to _libelf_write_elf().
+ * The library will do the object layout using the following
+ * ordering:
+ * - The executable header is placed first, are required by the
+ * ELF specification.
+ * - The program header table is placed immediately following the
+ * executable header.
+ * - Section data, if any, is placed after the program header
+ * table, aligned appropriately.
+ * - The section header table, if needed, is placed last.
*
- * File alignments:
- * PHDR - Addr
- * SHDR - Addr
+ * There are two sub-cases to be taken care of:
*
- * XXX: how do we handle 'flags'.
+ * - Case 2a: e->e_cmd == ELF_C_READ or ELF_C_RDWR
+ *
+ * In this sub-case, the underlying ELF object may already have
+ * content in it, which the application may have modified. The
+ * library will retrieve content from the existing object as
+ * needed.
+ *
+ * - Case 2b: e->e_cmd == ELF_C_WRITE
+ *
+ * The ELF object is being created afresh in this sub-case;
+ * there is no pre-existing content in the underlying ELF
+ * object.
*/
/*
* Compute the extents of a section, by looking at the data
- * descriptors associated with it. The function returns zero if an
- * error was detected. `*rc' holds the maximum file extent seen so
- * far.
+ * descriptors associated with it. The function returns 1 if
+ * successful, or zero if an error was detected.
*/
static int
-_libelf_compute_section_extents(Elf *e, Elf_Scn *s, off_t *rc)
+_libelf_compute_section_extents(Elf *e, Elf_Scn *s, off_t rc)
{
int ec;
- Elf_Data *d, *td;
+ size_t fsz, msz;
+ Elf_Data *d;
+ Elf32_Shdr *shdr32;
+ Elf64_Shdr *shdr64;
unsigned int elftype;
uint32_t sh_type;
uint64_t d_align;
uint64_t sh_align, sh_entsize, sh_offset, sh_size;
uint64_t scn_size, scn_alignment;
- /*
- * We need to recompute library private data structures if one
- * or more of the following is true:
- * - The underlying Shdr structure has been marked `dirty'. Significant
- * fields include: `sh_offset', `sh_type', `sh_size', `sh_addralign'.
- * - The Elf_Data structures part of this section have been marked
- * `dirty'. Affected members include `d_align', `d_offset', `d_type',
- * and `d_size'.
- * - The section as a whole is `dirty', e.g., it has been allocated
- * using elf_newscn(), or if a new Elf_Data structure was added using
- * elf_newdata().
- *
- * Each of these conditions would result in the ELF_F_DIRTY bit being
- * set on the section descriptor's `s_flags' field.
- */
-
ec = e->e_class;
+ shdr32 = &s->s_shdr.s_shdr32;
+ shdr64 = &s->s_shdr.s_shdr64;
if (ec == ELFCLASS32) {
- sh_type = s->s_shdr.s_shdr32.sh_type;
- sh_align = (uint64_t) s->s_shdr.s_shdr32.sh_addralign;
- sh_entsize = (uint64_t) s->s_shdr.s_shdr32.sh_entsize;
- sh_offset = (uint64_t) s->s_shdr.s_shdr32.sh_offset;
- sh_size = (uint64_t) s->s_shdr.s_shdr32.sh_size;
+ sh_type = shdr32->sh_type;
+ sh_align = (uint64_t) shdr32->sh_addralign;
+ sh_entsize = (uint64_t) shdr32->sh_entsize;
+ sh_offset = (uint64_t) shdr32->sh_offset;
+ sh_size = (uint64_t) shdr32->sh_size;
} else {
- sh_type = s->s_shdr.s_shdr64.sh_type;
- sh_align = s->s_shdr.s_shdr64.sh_addralign;
- sh_entsize = s->s_shdr.s_shdr64.sh_entsize;
- sh_offset = s->s_shdr.s_shdr64.sh_offset;
- sh_size = s->s_shdr.s_shdr64.sh_size;
+ sh_type = shdr64->sh_type;
+ sh_align = shdr64->sh_addralign;
+ sh_entsize = shdr64->sh_entsize;
+ sh_offset = shdr64->sh_offset;
+ sh_size = shdr64->sh_size;
}
- if (sh_type == SHT_NULL || sh_type == SHT_NOBITS)
- return (1);
-
- if ((s->s_flags & ELF_F_DIRTY) == 0) {
- if ((size_t) *rc < sh_offset + sh_size)
- *rc = sh_offset + sh_size;
- return (1);
- }
+ assert(sh_type != SHT_NULL && sh_type != SHT_NOBITS);
elftype = _libelf_xlate_shtype(sh_type);
if (elftype > ELF_T_LAST) {
@@ -131,15 +121,52 @@ _libelf_compute_section_extents(Elf *e,
return (0);
}
- /*
- * Compute the extent of the data descriptors associated with
- * this section.
- */
- scn_alignment = 0;
if (sh_align == 0)
sh_align = _libelf_falign(elftype, ec);
- /* Compute the section alignment. */
+ /*
+ * Check the section's data buffers for sanity and compute the
+ * section's alignment.
+ * Compute the section's size and alignment using the data
+ * descriptors associated with the section.
+ */
+ if (STAILQ_EMPTY(&s->s_data)) {
+ /*
+ * The section's content (if any) has not been read in
+ * yet. If section is not dirty marked dirty, we can
+ * reuse the values in the 'sh_size' and 'sh_offset'
+ * fields of the section header.
+ */
+ if ((s->s_flags & ELF_F_DIRTY) == 0) {
+ /*
+ * If the library is doing the layout, then we
+ * compute the new start offset for the
+ * section based on the current offset and the
+ * section's alignment needs.
+ *
+ * If the application is doing the layout, we
+ * can use the value in the 'sh_offset' field
+ * in the section header directly.
+ */
+ if (e->e_flags & ELF_F_LAYOUT)
+ goto updatedescriptor;
+ else
+ goto computeoffset;
+ }
+
+ /*
+ * Otherwise, we need to bring in the section's data
+ * from the underlying ELF object.
+ */
+ if (e->e_cmd != ELF_C_WRITE && elf_getdata(s, NULL) == NULL)
+ return (0);
+ }
+
+ /*
+ * Loop through the section's data descriptors.
+ */
+ scn_size = 0L;
+ scn_alignment = 0L;
STAILQ_FOREACH(d, &s->s_data, d_next) {
if (d->d_type > ELF_T_LAST) {
LIBELF_SET_ERROR(DATA, 0);
@@ -153,23 +180,40 @@ _libelf_compute_section_extents(Elf *e,
LIBELF_SET_ERROR(DATA, 0);
return (0);
}
- if (d_align > scn_alignment)
- scn_alignment = d_align;
- }
- scn_size = 0L;
+ /*
+ * The buffer's size should be a multiple of the
+ * memory size of the underlying type.
+ */
+ msz = _libelf_msize(d->d_type, ec, e->e_version);
+ if (d->d_size % msz) {
+ LIBELF_SET_ERROR(DATA, 0);
+ return (0);
+ }
- STAILQ_FOREACH_SAFE(d, &s->s_data, d_next, td) {
+ /*
+ * Compute the section's size.
+ */
if (e->e_flags & ELF_F_LAYOUT) {
if ((uint64_t) d->d_off + d->d_size > scn_size)
scn_size = d->d_off + d->d_size;
} else {
scn_size = roundup2(scn_size, d->d_align);
d->d_off = scn_size;
- scn_size += d->d_size;
+ fsz = _libelf_fsize(d->d_type, ec, d->d_version,
+ d->d_size / msz);
+ scn_size += fsz;
}
+
+ /*
+ * The section's alignment is the maximum alignment
+ * needed for its data buffers.
+ */
+ if (d_align > scn_alignment)
+ scn_alignment = d_align;
}
+
/*
* If the application is requesting full control over the layout
* of the section, check its values for sanity.
@@ -180,46 +224,60 @@ _libelf_compute_section_extents(Elf *e,
LIBELF_SET_ERROR(LAYOUT, 0);
return (0);
}
- } else {
- /*
- * Otherwise compute the values in the section header.
- */
+ goto updatedescriptor;
+ }
- if (scn_alignment > sh_align)
- sh_align = scn_alignment;
+ /*
+ * Otherwise compute the values in the section header.
+ *
+ * The section alignment is the maximum alignment for any of
+ * its contained data descriptors.
+ */
+ if (scn_alignment > sh_align)
+ sh_align = scn_alignment;
- /*
- * If the section entry size is zero, try and fill in an
- * appropriate entry size. Per the elf(5) manual page
- * sections without fixed-size entries should have their
- * 'sh_entsize' field set to zero.
- */
- if (sh_entsize == 0 &&
- (sh_entsize = _libelf_fsize(elftype, ec, e->e_version,
- (size_t) 1)) == 1)
- sh_entsize = 0;
+ /*
+ * If the section entry size is zero, try and fill in an
+ * appropriate entry size. Per the elf(5) manual page
+ * sections without fixed-size entries should have their
+ * 'sh_entsize' field set to zero.
+ */
+ if (sh_entsize == 0 &&
+ (sh_entsize = _libelf_fsize(elftype, ec, e->e_version,
+ (size_t) 1)) == 1)
+ sh_entsize = 0;
- sh_size = scn_size;
- sh_offset = roundup(*rc, sh_align);
+ sh_size = scn_size;
- if (ec == ELFCLASS32) {
- s->s_shdr.s_shdr32.sh_addralign = (uint32_t) sh_align;
- s->s_shdr.s_shdr32.sh_entsize = (uint32_t) sh_entsize;
- s->s_shdr.s_shdr32.sh_offset = (uint32_t) sh_offset;
- s->s_shdr.s_shdr32.sh_size = (uint32_t) sh_size;
- } else {
- s->s_shdr.s_shdr64.sh_addralign = sh_align;
- s->s_shdr.s_shdr64.sh_entsize = sh_entsize;
- s->s_shdr.s_shdr64.sh_offset = sh_offset;
- s->s_shdr.s_shdr64.sh_size = sh_size;
- }
- }
+computeoffset:
+ /*
+ * Compute the new offset for the section based on
+ * the section's alignment needs.
+ */
+ sh_offset = roundup(rc, sh_align);
- if ((size_t) *rc < sh_offset + sh_size)
- *rc = sh_offset + sh_size;
+ /*
+ * Update the section header.
+ */
+ if (ec == ELFCLASS32) {
+ shdr32->sh_addralign = (uint32_t) sh_align;
+ shdr32->sh_entsize = (uint32_t) sh_entsize;
+ shdr32->sh_offset = (uint32_t) sh_offset;
+ shdr32->sh_size = (uint32_t) sh_size;
+ } else {
+ shdr64->sh_addralign = sh_align;
+ shdr64->sh_entsize = sh_entsize;
+ shdr64->sh_offset = sh_offset;
+ shdr64->sh_size = sh_size;
+ }
+updatedescriptor:
+ /*
+ * Update the section descriptor.
+ */
s->s_size = sh_size;
s->s_offset = sh_offset;
+
return (1);
}
@@ -267,13 +325,16 @@ _libelf_insert_section(Elf *e, Elf_Scn *
return (1);
}
+/*
+ * Recompute section layout.
+ */
+
static off_t
_libelf_resync_sections(Elf *e, off_t rc)
{
int ec;
- off_t nrc;
+ Elf_Scn *s;
size_t sh_type, shdr_start, shdr_end;
- Elf_Scn *s, *ts;
ec = e->e_class;
@@ -281,13 +342,7 @@ _libelf_resync_sections(Elf *e, off_t rc
* Make a pass through sections, computing the extent of each
* section. Order in increasing order of addresses.
*/
-
- nrc = rc;
- STAILQ_FOREACH(s, &e->e_u.e_elf.e_scn, s_next)
- if (_libelf_compute_section_extents(e, s, &nrc) == 0)
- return ((off_t) -1);
-
- STAILQ_FOREACH_SAFE(s, &e->e_u.e_elf.e_scn, s_next, ts) {
+ STAILQ_FOREACH(s, &e->e_u.e_elf.e_scn, s_next) {
if (ec == ELFCLASS32)
sh_type = s->s_shdr.s_shdr32.sh_type;
else
@@ -296,21 +351,22 @@ _libelf_resync_sections(Elf *e, off_t rc
if (sh_type == SHT_NOBITS || sh_type == SHT_NULL)
continue;
- if (s->s_offset < (uint64_t) rc) {
- if (s->s_offset + s->s_size < (uint64_t) rc) {
- /*
- * Try insert this section in the
- * correct place in the list,
- * detecting overlaps if any.
- */
- STAILQ_REMOVE(&e->e_u.e_elf.e_scn, s, _Elf_Scn,
- s_next);
- if (_libelf_insert_section(e, s) == 0)
- return ((off_t) -1);
- } else {
- LIBELF_SET_ERROR(LAYOUT, 0);
+ if (_libelf_compute_section_extents(e, s, rc) == 0)
+ return ((off_t) -1);
+
+ if (s->s_size == 0)
+ continue;
+
+ if (s->s_offset + s->s_size < (size_t) rc) {
+ /*
+ * Try insert this section in the
+ * correct place in the list,
+ * detecting overlaps if any.
+ */
+ STAILQ_REMOVE(&e->e_u.e_elf.e_scn, s, _Elf_Scn,
+ s_next);
+ if (_libelf_insert_section(e, s) == 0)
return ((off_t) -1);
- }
} else
rc = s->s_offset + s->s_size;
}
@@ -338,8 +394,6 @@ _libelf_resync_sections(Elf *e, off_t rc
}
}
- assert(nrc == rc);
-
return (rc);
}
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