Re: [PATCH v5 4/6] livepatch: reuse module loader code to write relocations

On Mon, Mar 21, 2016 at 05:31:57PM +0100, Petr Mladek wrote:

quoted

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 780f00c..2aa20fa 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
+static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
+{
+	int i, cnt, vmlinux, ret;
+	struct klp_buf bufs = {0};
+	Elf_Rela *relas;
+	Elf_Sym *sym;
+	char *symname;
+	unsigned long sympos;
+
+	relas = (Elf_Rela *) relasec->sh_addr;
+	/* For each rela in this klp relocation section */
+	for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
+		sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
+		if (sym->st_shndx != SHN_LIVEPATCH)
+			return -EINVAL;
+
+		klp_clear_buf(&bufs);
+
+		/* Format: .klp.sym.objname.symbol_name,sympos */
+		symname = pmod->core_kallsyms.strtab + sym->st_name;
+		cnt = sscanf(symname, ".klp.sym.%64[^.].%128[^,],%lu",
+			     bufs.objname, bufs.symname, &sympos);

Note that MODULE_NAME_LEN even is not 64. It is defined by:

#define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))

I strongly suggest to use the proposal from Josh.

Hm, looks like my suggestion to use __stringify(MODULE_NAME_LEN) doesn't
work.  It results in the string "MODULE_NAME_LEN".  Which surprises me:
isn't is supposed to resolve the macro before applying the '#' operation
to it?

I was going to suggest another idea: hard-code it at 63 and then do
something like

  BUILD_BUG_ON(MODULE_NAME_LEN != 64)

But you're right... it's not even 64!

Need to think on this some more...

-- 
Josh