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Merge "Make the linker relocatable."

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This commit is contained in:
Nick Kralevich 2012-05-15 15:10:24 -07:00 committed by android code review
commit cf8e554c72
3 changed files with 121 additions and 44 deletions
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22
linker/Android.mk
View file

@ -10,27 +10,9 @@ LOCAL_SRC_FILES:= \
dlfcn.c \
debugger.c
ifeq ($(TARGET_ARCH),sh)
# SH-4A series virtual address range from 0x00000000 to 0x7FFFFFFF.
LINKER_TEXT_BASE := 0x70000100
else
# This is aligned to 4K page boundary so that both GNU ld and gold work. Gold
# actually produces a correct binary with starting address 0xB0000100 but the
# extra objcopy step to rename symbols causes the resulting binary to be misaligned
# and unloadable. Increasing the alignment adds an extra 3840 bytes in padding
# but switching to gold saves about 1M of space.
LINKER_TEXT_BASE := 0xB0001000
endif
LOCAL_LDFLAGS := -shared
# The maximum size set aside for the linker, from
# LINKER_TEXT_BASE rounded down to a megabyte.
LINKER_AREA_SIZE := 0x01000000
LOCAL_LDFLAGS := -Wl,-Ttext,$(LINKER_TEXT_BASE)
LOCAL_CFLAGS += -DPRELINK
LOCAL_CFLAGS += -DLINKER_TEXT_BASE=$(LINKER_TEXT_BASE)
LOCAL_CFLAGS += -DLINKER_AREA_SIZE=$(LINKER_AREA_SIZE)
LOCAL_CFLAGS += -fno-stack-protector
# Set LINKER_DEBUG to either 1 or 0
#

142
linker/linker.c
View file

@ -313,15 +313,6 @@ static void free_info(soinfo *si)
freelist = si;
}
#ifndef LINKER_TEXT_BASE
#error "linker's makefile must define LINKER_TEXT_BASE"
#endif
#ifndef LINKER_AREA_SIZE
#error "linker's makefile must define LINKER_AREA_SIZE"
#endif
#define LINKER_BASE ((LINKER_TEXT_BASE) & 0xfff00000)
#define LINKER_TOP (LINKER_BASE + (LINKER_AREA_SIZE))
const char *addr_to_name(unsigned addr)
{
soinfo *si;
@ -332,10 +323,6 @@ const char *addr_to_name(unsigned addr)
}
}
if((addr >= LINKER_BASE) && (addr < LINKER_TOP)){
return "linker";
}
return "";
}
@ -354,12 +341,10 @@ _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount)
soinfo *si;
unsigned addr = (unsigned)pc;
if ((addr < LINKER_BASE) || (addr >= LINKER_TOP)) {
for (si = solist; si != 0; si = si->next){
if ((addr >= si->base) && (addr < (si->base + si->size))) {
*pcount = si->ARM_exidx_count;
return (_Unwind_Ptr)(si->base + (unsigned long)si->ARM_exidx);
}
for (si = solist; si != 0; si = si->next){
if ((addr >= si->base) && (addr < (si->base + si->size))) {
*pcount = si->ARM_exidx_count;
return (_Unwind_Ptr)(si->base + (unsigned long)si->ARM_exidx);
}
}
*pcount = 0;
@ -420,6 +405,33 @@ static Elf32_Sym *_elf_lookup(soinfo *si, unsigned hash, const char *name)
return NULL;
}
/*
* Essentially the same method as _elf_lookup() above, but only
* searches for LOCAL symbols
*/
static Elf32_Sym *_elf_lookup_local(soinfo *si, unsigned hash, const char *name)
{
Elf32_Sym *symtab = si->symtab;
const char *strtab = si->strtab;
unsigned n = hash % si->nbucket;;
TRACE_TYPE(LOOKUP, "%5d LOCAL SEARCH %s in %s@0x%08x %08x %d\n", pid,
name, si->name, si->base, hash, hash % si->nbucket);
for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){
Elf32_Sym *s = symtab + n;
if (strcmp(strtab + s->st_name, name)) continue;
if (ELF32_ST_BIND(s->st_info) != STB_LOCAL) continue;
/* no section == undefined */
if(s->st_shndx == 0) continue;
TRACE_TYPE(LOOKUP, "%5d FOUND LOCAL %s in %s (%08x) %d\n", pid,
name, si->name, s->st_value, s->st_size);
return s;
}
return NULL;
}
static unsigned elfhash(const char *_name)
{
const unsigned char *name = (const unsigned char *) _name;
@ -443,7 +455,17 @@ _do_lookup(soinfo *si, const char *name, unsigned *base)
soinfo *lsi = si;
int i;
/* Look for symbols in the local scope first (the object who is
/* If we are trying to find a symbol for the linker itself, look
* for LOCAL symbols first. Avoid using LOCAL symbols for other
* shared libraries until we have a better understanding of what
* might break by doing so. */
if (si->flags & FLAG_LINKER) {
s = _elf_lookup_local(si, elf_hash, name);
if(s != NULL)
goto done;
}
/* Look for symbols in the local scope (the object who is
* searching). This happens with C++ templates on i386 for some
* reason.
*
@ -452,6 +474,7 @@ _do_lookup(soinfo *si, const char *name, unsigned *base)
* 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 = _elf_lookup(si, elf_hash, name);
if(s != NULL)
goto done;
@ -1628,10 +1651,10 @@ static int link_image(soinfo *si, unsigned wr_offset)
DEBUG("%5d si->base = 0x%08x si->flags = 0x%08x\n", pid,
si->base, si->flags);
if (si->flags & FLAG_EXE) {
if (si->flags & (FLAG_EXE | FLAG_LINKER)) {
/* Locate the needed program segments (DYNAMIC/ARM_EXIDX) for
* linkage info if this is the executable. If this was a
* dynamic lib, that would have been done at load time.
* linkage info if this is the executable or the linker itself.
* If this was a dynamic lib, that would have been done at load time.
*
* TODO: It's unfortunate that small pieces of this are
* repeated from the load_library routine. Refactor this just
@ -1958,7 +1981,12 @@ int main(int argc, char **argv)
static void * __tls_area[ANDROID_TLS_SLOTS];
unsigned __linker_init(unsigned **elfdata)
/*
* This code is called after the linker has linked itself and
* fixed it's own GOT. It is safe to make references to externs
* and other non-local data at this point.
*/
static unsigned __linker_init_post_relocation(unsigned **elfdata)
{
static soinfo linker_soinfo;
@ -2158,3 +2186,69 @@ sanitize:
si->entry);
return si->entry;
}
/*
* Find the value of AT_BASE passed to us by the kernel. This is the load
* location of the linker.
*/
static unsigned find_linker_base(unsigned **elfdata) {
int argc = (int) *elfdata;
char **argv = (char**) (elfdata + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1);
while (vecs[0] != 0) {
vecs++;
}
/* The end of the environment block is marked by two NULL pointers */
vecs++;
while(vecs[0]) {
if (vecs[0] == AT_BASE) {
return vecs[1];
}
vecs += 2;
}
return 0; // should never happen
}
/*
* This is the entry point for the linker, called from begin.S. This
* method is responsible for fixing the linker's own relocations, and
* then calling __linker_init_post_relocation().
*
* Because this method is called before the linker has fixed it's own
* relocations, any attempt to reference an extern variable, extern
* function, or other GOT reference will generate a segfault.
*/
unsigned __linker_init(unsigned **elfdata) {
unsigned linker_addr = find_linker_base(elfdata);
Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr;
Elf32_Phdr *phdr =
(Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff);
soinfo linker_so;
memset(&linker_so, 0, sizeof(soinfo));
linker_so.base = linker_addr;
linker_so.dynamic = (unsigned *) -1;
linker_so.phdr = phdr;
linker_so.phnum = elf_hdr->e_phnum;
linker_so.flags |= FLAG_LINKER;
linker_so.wrprotect_start = 0xffffffff;
linker_so.wrprotect_end = 0;
if (link_image(&linker_so, 0)) {
// It would be nice to print an error message, but if the linker
// can't link itself, there's no guarantee that we'll be able to
// call write() (because it involves a GOT reference).
//
// This situation should never occur unless the linker itself
// is corrupt.
exit(-1);
}
// We have successfully fixed our own relocations. It's safe to run
// the main part of the linker now.
return __linker_init_post_relocation(elfdata);
}

1
linker/linker.h
View file

@ -83,6 +83,7 @@ typedef struct soinfo soinfo;
#define FLAG_LINKED 0x00000001
#define FLAG_ERROR 0x00000002
#define FLAG_EXE 0x00000004 // The main executable
#define FLAG_LINKER 0x00000010 // The linker itself
#define SOINFO_NAME_LEN 128