Re: [RFC PATCH v3 4/6] livepatch: reuse module loader code to write relocations

Hi Jessica,

I walked through the series and it looks really nice. Others have already 
pointed out the issues I also found, so only few minor things below.

First thing, could you copy&paste the information and reasoning from the 
cover letter to the changelogs where appropriate? It is very detailed and 
it would be a pity to lost it.

On Fri, 8 Jan 2016, Jessica Yu wrote:

You left klp_write_module_reloc() in arch/s390/include/asm/livepatch.h I'm 
afraid. Anyway it would be really great if you managed to test the series 
on s390 somehow. Just to know that all the roadblocks are really gone.

-/*
- * external symbols are located outside the parent object (where the parent
- * object is either vmlinux or the kmod being patched).
- */
-static int klp_find_external_symbol(struct module *pmod, const char *name,
-				    unsigned long *addr)
+static int klp_resolve_symbols(Elf_Shdr *relsec, struct module *pmod)
 {
-	const struct kernel_symbol *sym;
+	int i, len, ret = 0;
+	Elf_Rela *relas;
+	Elf_Sym *sym;
+	char *symname, *sym_objname;
 
-	/* first, check if it's an exported symbol */
-	preempt_disable();
-	sym = find_symbol(name, NULL, NULL, true, true);
-	if (sym) {
-		*addr = sym->value;
-		preempt_enable();
-		return 0;
+	relas = (Elf_Rela *) relsec->sh_addr;
+	/* For each rela in this .klp.rel. section */
+	for (i = 0; i < relsec->sh_size / sizeof(Elf_Rela); i++) {
+		sym = pmod->core_symtab + ELF_R_SYM(relas[i].r_info);
+		symname = pmod->core_strtab + sym->st_name;

Maybe it would be better to use pmod->symtab and pmod->strtab everywhere. 
It should be the same, but core_* versions are only helpers used in 
load_module and friends. There is even a comment in 
include/linux/module.h.

	/*
	 * We keep the symbol and string tables for kallsyms.
	 * The core_* fields below are temporary, loader-only (they
	 * could really be discarded after module init).
	 */

We should respect that.

Thanks,
Miroslav