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Adjust symbol lookup for DT_SYMBOLIC case

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According ELF spec re. DT_SYMBOLIC:
This element's presence in a shared object library alters the dynamic
linker's symbol resolution algorithm for references within the library.
Instead of starting a symbol search with the executable file, the
dynamic linker starts from the shared object itself. If the shared
object fails to supply the referenced symbol, the dynamic linker then
searches the executable file and other shared objects as usual.

This change implements the last part.

Change-Id: Iae95d53d455313a4306f11733941bcd3596ac85f
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
This commit is contained in:
Pavel Chupin 2012-10-31 13:55:51 +04:00
parent 084be59192
commit c77c434149
1 changed files with 53 additions and 23 deletions
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76
linker/linker.cpp Normal file → Executable file
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@ -425,38 +425,68 @@ soinfo_do_lookup(soinfo *si, const char *name, soinfo **lsi,
Elf32_Sym *s = NULL;
int i;
if (si != NULL) {
if (si != NULL && somain != NULL) {
/*
* If this object was built with symbolic relocations disabled, the
* first place to look to resolve external references is the main
* executable.
* Local scope is executable scope. Just start looking into it right away
* for the shortcut.
*/
if (!si->has_DT_SYMBOLIC) {
DEBUG("%5d %s: looking up %s in executable %s\n",
pid, si->name, name, somain->name);
s = soinfo_elf_lookup(somain, elf_hash, name);
if (si == somain) {
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*lsi = somain;
*lsi = si;
goto done;
}
}
} else {
/* Order of symbol lookup is controlled by DT_SYMBOLIC flag */
/* Look for symbols in the local scope (the object who is
* searching). This happens with C++ templates on i386 for some
* reason.
*
* Notes on weak symbols:
* The ELF specs are ambiguous about treatment of weak definitions in
* dynamic linking. Some systems return the first definition found
* and some the first non-weak definition. This is system dependent.
* Here we return the first definition found for simplicity. */
/*
* If this object was built with symbolic relocations disabled, the
* first place to look to resolve external references is the main
* executable.
*/
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*lsi = si;
goto done;
if (!si->has_DT_SYMBOLIC) {
DEBUG("%5d %s: looking up %s in executable %s\n",
pid, si->name, name, somain->name);
s = soinfo_elf_lookup(somain, elf_hash, name);
if (s != NULL) {
*lsi = somain;
goto done;
}
}
/* Look for symbols in the local scope (the object who is
* searching). This happens with C++ templates on i386 for some
* reason.
*
* Notes on weak symbols:
* The ELF specs are ambiguous about treatment of weak definitions in
* dynamic linking. Some systems return the first definition found
* and some the first non-weak definition. This is system dependent.
* Here we return the first definition found for simplicity. */
s = soinfo_elf_lookup(si, elf_hash, name);
if (s != NULL) {
*lsi = si;
goto done;
}
/*
* If this object was built with -Bsymbolic and symbol is not found
* in the local scope, try to find the symbol in the main executable.
*/
if (si->has_DT_SYMBOLIC) {
DEBUG("%5d %s: looking up %s in executable %s after local scope\n",
pid, si->name, name, somain->name);
s = soinfo_elf_lookup(somain, elf_hash, name);
if (s != NULL) {
*lsi = somain;
goto done;
}
}
}
}