linker: rename load_offset to load_bias.
This patch changes the definition of the 'load_offset' field
in struct soinfo. The field is renamed because it is not the
basic load bias to add to every p_vaddr value read from the ELF
file to get the corresponding memory address.
This also slightly simplifies the relocation code.
+ Fix for proper load_bias computation for relocatable executables.
Change-Id: I72502c75a70751cba324deee7d313ae61f96609e
diff --git a/linker/linker.c b/linker/linker.c
index 1bf017f..c725d02 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -424,7 +424,7 @@
}
static Elf32_Sym *
-soinfo_do_lookup(soinfo *si, const char *name, unsigned *base, Elf32_Addr *offset)
+soinfo_do_lookup(soinfo *si, const char *name, Elf32_Addr *offset)
{
unsigned elf_hash = elfhash(name);
Elf32_Sym *s;
@@ -487,11 +487,10 @@
done:
if(s != NULL) {
TRACE_TYPE(LOOKUP, "%5d si %s sym %s s->st_value = 0x%08x, "
- "found in %s, base = 0x%08x, load offset = 0x%08x\n",
+ "found in %s, base = 0x%08x, load bias = 0x%08x\n",
pid, si->name, name, s->st_value,
- lsi->name, lsi->base, lsi->load_offset);
- *base = lsi->base;
- *offset = lsi->load_offset;
+ lsi->name, lsi->base, lsi->load_bias);
+ *offset = lsi->load_bias;
return s;
}
@@ -812,13 +811,13 @@
* header table appear in ascending order, sorted on the
* p_vaddr member."
*/
- si->load_offset = PAGE_START(phdr->p_vaddr);
+ si->load_bias = si->base - PAGE_START(phdr->p_vaddr);
break;
}
}
/* "base" might wrap around UINT32_MAX. */
- base = (Elf32_Addr)(si->base - si->load_offset);
+ base = si->load_bias;
/* Now go through all the PT_LOAD segments and map them into memory
* at the appropriate locations. */
@@ -1271,7 +1270,7 @@
for (idx = 0; idx < count; ++idx) {
unsigned type = ELF32_R_TYPE(rel->r_info);
unsigned sym = ELF32_R_SYM(rel->r_info);
- unsigned reloc = (unsigned)(rel->r_offset + si->base - si->load_offset);
+ unsigned reloc = (unsigned)(rel->r_offset + si->load_bias);
unsigned sym_addr = 0;
char *sym_name = NULL;
@@ -1279,7 +1278,7 @@
si->name, idx);
if(sym != 0) {
sym_name = (char *)(strtab + symtab[sym].st_name);
- s = soinfo_do_lookup(si, sym_name, &base, &offset);
+ s = soinfo_do_lookup(si, sym_name, &offset);
if(s == NULL) {
/* We only allow an undefined symbol if this is a weak
reference.. */
@@ -1346,7 +1345,7 @@
return -1;
}
#endif
- sym_addr = (unsigned)(s->st_value + base - offset);
+ sym_addr = (unsigned)(s->st_value + offset);
}
COUNT_RELOC(RELOC_SYMBOL);
} else {
@@ -1652,7 +1651,7 @@
{
unsigned *d;
/* "base" might wrap around UINT32_MAX. */
- Elf32_Addr base = si->base - si->load_offset;
+ Elf32_Addr base = si->load_bias;
Elf32_Phdr *phdr = si->phdr;
int phnum = si->phnum;
@@ -2128,13 +2127,14 @@
*/
int nn;
si->base = 0;
+ si->load_bias = 0;
for ( nn = 0; nn < si->phnum; nn++ ) {
if (si->phdr[nn].p_type == PT_PHDR) {
- si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_vaddr;
+ si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr;
+ si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset;
break;
}
}
- si->load_offset = 0;
si->dynamic = (unsigned *)-1;
si->wrprotect_start = 0xffffffff;
si->wrprotect_end = 0;
@@ -2233,6 +2233,32 @@
return 0; // should never happen
}
+/* Compute the load-bias of an existing executable. This shall only
+ * be used to compute the load bias of an executable or shared library
+ * that was loaded by the kernel itself.
+ *
+ * Input:
+ * elf -> address of ELF header, assumed to be at the start of the file.
+ * Return:
+ * load bias, i.e. add the value of any p_vaddr in the file to get
+ * the corresponding address in memory.
+ */
+static Elf32_Addr
+get_elf_exec_load_bias(const Elf32_Ehdr* elf)
+{
+ Elf32_Addr offset = elf->e_phoff;
+ const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset);
+ const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum;
+ const Elf32_Phdr* phdr;
+
+ for (phdr = phdr_table; phdr < phdr_end; phdr++) {
+ if (phdr->p_type == PT_LOAD) {
+ return (Elf32_Addr)elf + phdr->p_offset - phdr->p_vaddr;
+ }
+ }
+ return 0;
+}
+
/*
* This is the entry point for the linker, called from begin.S. This
* method is responsible for fixing the linker's own relocations, and
@@ -2252,7 +2278,7 @@
memset(&linker_so, 0, sizeof(soinfo));
linker_so.base = linker_addr;
- linker_so.load_offset = 0;
+ linker_so.load_bias = get_elf_exec_load_bias(elf_hdr);
linker_so.dynamic = (unsigned *) -1;
linker_so.phdr = phdr;
linker_so.phnum = elf_hdr->e_phnum;