#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/module.h>
+#include <linux/sort.h>
#include <asm/cache.h>
#include <asm/opcodes.h>
u32 lit[PLT_ENT_COUNT];
};
-static bool in_init(const struct module *mod, u32 addr)
+u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
- return addr - (u32)mod->init_layout.base < mod->init_layout.size;
+ struct plt_entries *plt = (struct plt_entries *)mod->arch.plt->sh_addr;
+ int idx = 0;
+
+ /*
+ * Look for an existing entry pointing to 'val'. Given that the
+ * relocations are sorted, this will be the last entry we allocated.
+ * (if one exists).
+ */
+ if (mod->arch.plt_count > 0) {
+ plt += (mod->arch.plt_count - 1) / PLT_ENT_COUNT;
+ idx = (mod->arch.plt_count - 1) % PLT_ENT_COUNT;
+
+ if (plt->lit[idx] == val)
+ return (u32)&plt->ldr[idx];
+
+ idx = (idx + 1) % PLT_ENT_COUNT;
+ if (!idx)
+ plt++;
+ }
+
+ mod->arch.plt_count++;
+ BUG_ON(mod->arch.plt_count * PLT_ENT_SIZE > mod->arch.plt->sh_size);
+
+ if (!idx)
+ /* Populate a new set of entries */
+ *plt = (struct plt_entries){
+ { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
+ { val, }
+ };
+ else
+ plt->lit[idx] = val;
+
+ return (u32)&plt->ldr[idx];
}
-u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
+#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
+
+static int cmp_rel(const void *a, const void *b)
{
- struct plt_entries *plt, *plt_end;
- int c, *count;
-
- if (in_init(mod, loc)) {
- plt = (void *)mod->arch.init_plt->sh_addr;
- plt_end = (void *)plt + mod->arch.init_plt->sh_size;
- count = &mod->arch.init_plt_count;
- } else {
- plt = (void *)mod->arch.core_plt->sh_addr;
- plt_end = (void *)plt + mod->arch.core_plt->sh_size;
- count = &mod->arch.core_plt_count;
- }
+ const Elf32_Rel *x = a, *y = b;
+ int i;
- /* Look for an existing entry pointing to 'val' */
- for (c = *count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
- int i;
-
- if (!c) {
- /* Populate a new set of entries */
- *plt = (struct plt_entries){
- { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
- { val, }
- };
- ++*count;
- return (u32)plt->ldr;
- }
- for (i = 0; i < PLT_ENT_COUNT; i++) {
- if (!plt->lit[i]) {
- plt->lit[i] = val;
- ++*count;
- }
- if (plt->lit[i] == val)
- return (u32)&plt->ldr[i];
- }
+ /* sort by type and symbol index */
+ i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
+ if (i == 0)
+ i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
+ return i;
+}
+
+static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
+{
+ u32 *tval = (u32 *)(base + rel->r_offset);
+
+ /*
+ * Do a bitwise compare on the raw addend rather than fully decoding
+ * the offset and doing an arithmetic comparison.
+ * Note that a zero-addend jump/call relocation is encoded taking the
+ * PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
+ */
+ switch (ELF32_R_TYPE(rel->r_info)) {
+ u16 upper, lower;
+
+ case R_ARM_THM_CALL:
+ case R_ARM_THM_JUMP24:
+ upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
+ lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);
+
+ return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;
+
+ case R_ARM_CALL:
+ case R_ARM_PC24:
+ case R_ARM_JUMP24:
+ return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
}
BUG();
}
-static int duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num,
- u32 mask)
+static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
{
- u32 *loc1, *loc2;
- int i;
+ const Elf32_Rel *prev;
- for (i = 0; i < num; i++) {
- if (rel[i].r_info != rel[num].r_info)
- continue;
+ /*
+ * Entries are sorted by type and symbol index. That means that,
+ * if a duplicate entry exists, it must be in the preceding
+ * slot.
+ */
+ if (!num)
+ return false;
- /*
- * Identical relocation types against identical symbols can
- * still result in different PLT entries if the addend in the
- * place is different. So resolve the target of the relocation
- * to compare the values.
- */
- loc1 = (u32 *)(base + rel[i].r_offset);
- loc2 = (u32 *)(base + rel[num].r_offset);
- if (((*loc1 ^ *loc2) & mask) == 0)
- return 1;
- }
- return 0;
+ prev = rel + num - 1;
+ return cmp_rel(rel + num, prev) == 0 &&
+ is_zero_addend_relocation(base, prev);
}
/* Count how many PLT entries we may need */
-static unsigned int count_plts(Elf32_Addr base, const Elf32_Rel *rel, int num)
+static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
+ const Elf32_Rel *rel, int num)
{
unsigned int ret = 0;
+ const Elf32_Sym *s;
int i;
- /*
- * Sure, this is order(n^2), but it's usually short, and not
- * time critical
- */
- for (i = 0; i < num; i++)
+ for (i = 0; i < num; i++) {
switch (ELF32_R_TYPE(rel[i].r_info)) {
case R_ARM_CALL:
case R_ARM_PC24:
case R_ARM_JUMP24:
- if (!duplicate_rel(base, rel, i,
- __opcode_to_mem_arm(0x00ffffff)))
- ret++;
- break;
-#ifdef CONFIG_THUMB2_KERNEL
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
- if (!duplicate_rel(base, rel, i,
- __opcode_to_mem_thumb32(0x07ff2fff)))
+ /*
+ * We only have to consider branch targets that resolve
+ * to undefined symbols. This is not simply a heuristic,
+ * it is a fundamental limitation, since the PLT itself
+ * is part of the module, and needs to be within range
+ * as well, so modules can never grow beyond that limit.
+ */
+ s = syms + ELF32_R_SYM(rel[i].r_info);
+ if (s->st_shndx != SHN_UNDEF)
+ break;
+
+ /*
+ * Jump relocations with non-zero addends against
+ * undefined symbols are supported by the ELF spec, but
+ * do not occur in practice (e.g., 'jump n bytes past
+ * the entry point of undefined function symbol f').
+ * So we need to support them, but there is no need to
+ * take them into consideration when trying to optimize
+ * this code. So let's only check for duplicates when
+ * the addend is zero.
+ */
+ if (!is_zero_addend_relocation(base, rel + i) ||
+ !duplicate_rel(base, rel, i))
ret++;
-#endif
}
+ }
return ret;
}
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
- unsigned long core_plts = 0, init_plts = 0;
+ unsigned long plts = 0;
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
+ Elf32_Sym *syms = NULL;
/*
* To store the PLTs, we expand the .text section for core module code
- * and the .init.text section for initialization code.
+ * and for initialization code.
*/
- for (s = sechdrs; s < sechdrs_end; ++s)
- if (strcmp(".core.plt", secstrings + s->sh_name) == 0)
- mod->arch.core_plt = s;
- else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
- mod->arch.init_plt = s;
-
- if (!mod->arch.core_plt || !mod->arch.init_plt) {
- pr_err("%s: sections missing\n", mod->name);
+ for (s = sechdrs; s < sechdrs_end; ++s) {
+ if (strcmp(".plt", secstrings + s->sh_name) == 0)
+ mod->arch.plt = s;
+ else if (s->sh_type == SHT_SYMTAB)
+ syms = (Elf32_Sym *)s->sh_addr;
+ }
+
+ if (!mod->arch.plt) {
+ pr_err("%s: module PLT section missing\n", mod->name);
+ return -ENOEXEC;
+ }
+ if (!syms) {
+ pr_err("%s: module symtab section missing\n", mod->name);
return -ENOEXEC;
}
for (s = sechdrs + 1; s < sechdrs_end; ++s) {
- const Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
+ Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
int numrels = s->sh_size / sizeof(Elf32_Rel);
Elf32_Shdr *dstsec = sechdrs + s->sh_info;
if (s->sh_type != SHT_REL)
continue;
- if (strstr(secstrings + s->sh_name, ".init"))
- init_plts += count_plts(dstsec->sh_addr, rels, numrels);
- else
- core_plts += count_plts(dstsec->sh_addr, rels, numrels);
+ /* ignore relocations that operate on non-exec sections */
+ if (!(dstsec->sh_flags & SHF_EXECINSTR))
+ continue;
+
+ /* sort by type and symbol index */
+ sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);
+
+ plts += count_plts(syms, dstsec->sh_addr, rels, numrels);
}
- mod->arch.core_plt->sh_type = SHT_NOBITS;
- mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
- mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES;
- mod->arch.core_plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
- sizeof(struct plt_entries));
- mod->arch.core_plt_count = 0;
-
- mod->arch.init_plt->sh_type = SHT_NOBITS;
- mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
- mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES;
- mod->arch.init_plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
- sizeof(struct plt_entries));
- mod->arch.init_plt_count = 0;
- pr_debug("%s: core.plt=%x, init.plt=%x\n", __func__,
- mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size);
+ mod->arch.plt->sh_type = SHT_NOBITS;
+ mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ mod->arch.plt->sh_addralign = L1_CACHE_BYTES;
+ mod->arch.plt->sh_size = round_up(plts * PLT_ENT_SIZE,
+ sizeof(struct plt_entries));
+ mod->arch.plt_count = 0;
+
+ pr_debug("%s: plt=%x\n", __func__, mod->arch.plt->sh_size);
return 0;
}
projects / cascardo / linux.git / commitdiff