Author: emaste
Date: Thu Oct 25 13:46:28 2018
New Revision: 339710
URL: https://svnweb.freebsd.org/changeset/base/339710
Log:
elfcopy: avoid stripping relocations from static binaries
MFC r339350: elfcopy: delete filter_reloc, it is broken and unnecessary
elfcopy contained logic to filter individual relocations in STRIP_ALL
mode. However, this is not valid; relocations emitted by the linker are
required, unless they apply to an entire section being removed (which is
handled by other logic in elfcopy).
Note that filter_reloc was also buggy: for RELA relocation sections it
operated on uninitialized rel.r_info resulting in invalid operation.
The logic most likely needs to be inverted: instead of removing
relocations because their associated symbols are being removed, we must
keep symbols referenced by relocations. That said, in practice we do
not encounter this code path today: objects being stripped are either
dynamically linked binaries which retain .dynsym, or static binaries
with no relocations.
Just remove filter_reloc. This fixes certain cases including statically
linked binaries containing ifuncs. Stripping binaries with relocations
referencing removed symbols was already broken, and after this change
may still be broken in a different way.
MFC r339451: objcopy: restore behaviour required by GCC's build
In r339350 filter_reloc() was removed, to fix the case of stripping
statically linked binaries with relocations (which may come from ifunc
use, for example). As a side effect this changed the behaviour when
stripping object files - the output was broken both before and after
r339350, in different ways. Unfortunately GCC's build process relies
on the previous behaviour, so:
- Revert r339350, restoring filter_reloc().
- Fix an unitialized variable use (commited as r3638 in ELF Tool Chain).
- Change filter_reloc() to omit relocations referencing removed
symbols, while retaining relocations with no symbol reference.
- Retain the entire relocation section if it references the dynamic
symbol table (fix from kaiw in D17596).
PR: 232176
Sponsored by: The FreeBSD Foundation
Modified:
stable/11/contrib/elftoolchain/elfcopy/sections.c
Directory Properties:
stable/11/ (props changed)
Modified: stable/11/contrib/elftoolchain/elfcopy/sections.c
==============================================================================
--- stable/11/contrib/elftoolchain/elfcopy/sections.c Thu Oct 25 13:37:57
2018 (r339709)
+++ stable/11/contrib/elftoolchain/elfcopy/sections.c Thu Oct 25 13:46:28
2018 (r339710)
@@ -689,7 +689,7 @@ filter_reloc(struct elfcopy *ecp, struct section *s)
Elf32_Rela *rela32;
Elf64_Rela *rela64;
Elf_Data *id;
- uint64_t cap, n, nrels;
+ uint64_t cap, n, nrels, sym;
int elferr, i;
if (gelf_getshdr(s->is, &ish) == NULL)
@@ -698,15 +698,13 @@ filter_reloc(struct elfcopy *ecp, struct section *s)
/* We don't want to touch relocation info for dynamic symbols. */
if ((ecp->flags & SYMTAB_EXIST) == 0) {
- if (ish.sh_link == 0 || ecp->secndx[ish.sh_link] == 0) {
- /*
- * This reloc section applies to the symbol table
- * that was stripped, so discard whole section.
- */
- s->nocopy = 1;
- s->sz = 0;
- }
- return;
+ /*
+ * No symbol table in output. If sh_link points to a section
+ * that exists in the output object, this relocation section
+ * is for dynamic symbols. Don't touch it.
+ */
+ if (ish.sh_link != 0 && ecp->secndx[ish.sh_link] != 0)
+ return;
} else {
/* Symbol table exist, check if index equals. */
if (ish.sh_link != elf_ndxscn(ecp->symtab->is))
@@ -747,28 +745,45 @@ filter_reloc(struct elfcopy *ecp, struct section *s)
if (gelf_getrel(id, i, &rel) != &rel)
errx(EXIT_FAILURE, "gelf_getrel failed: %s",
elf_errmsg(-1));
+ sym = GELF_R_SYM(rel.r_info);
} else {
if (gelf_getrela(id, i, &rela) != &rela)
errx(EXIT_FAILURE, "gelf_getrel failed: %s",
elf_errmsg(-1));
+ sym = GELF_R_SYM(rela.r_info);
}
- name = elf_strptr(ecp->ein, elf_ndxscn(ecp->strtab->is),
- GELF_R_SYM(rel.r_info));
- if (name == NULL)
- errx(EXIT_FAILURE, "elf_strptr failed: %s",
- elf_errmsg(-1));
- if (lookup_symop_list(ecp, name, SYMOP_KEEP) != NULL) {
- if (ecp->oec == ELFCLASS32) {
- if (s->type == SHT_REL)
- COPYREL(rel, 32);
- else
- COPYREL(rela, 32);
- } else {
- if (s->type == SHT_REL)
- COPYREL(rel, 64);
- else
- COPYREL(rela, 64);
- }
+ /*
+ * If a relocation references a symbol and we are omitting
+ * either that symbol or the entire symbol table we cannot
+ * produce valid output, and so just omit the relocation.
+ * Broken output like this is generally not useful, but some
+ * uses of elfcopy/strip rely on it - for example, GCC's build
+ * process uses it to check for build reproducibility by
+ * stripping objects and comparing them.
+ *
+ * Relocations that do not reference a symbol are retained.
+ */
+ if (sym != 0) {
+ if (ish.sh_link == 0 || ecp->secndx[ish.sh_link] == 0)
+ continue;
+ name = elf_strptr(ecp->ein, elf_ndxscn(ecp->strtab->is),
+ sym);
+ if (name == NULL)
+ errx(EXIT_FAILURE, "elf_strptr failed: %s",
+ elf_errmsg(-1));
+ if (lookup_symop_list(ecp, name, SYMOP_KEEP) == NULL)
+ continue;
+ }
+ if (ecp->oec == ELFCLASS32) {
+ if (s->type == SHT_REL)
+ COPYREL(rel, 32);
+ else
+ COPYREL(rela, 32);
+ } else {
+ if (s->type == SHT_REL)
+ COPYREL(rel, 64);
+ else
+ COPYREL(rela, 64);
}
}
elferr = elf_errno();
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