kpatch-build: Support gcc-6 function prologue

With gcc-6 the function prologue is changeg by
moving the toc base resolution func - 0x8 bytes:

        .globl my_func
        .type my_func, @function
        .quad .TOC.-my_func
my_func:
        .reloc ., R_PPC64_ENTRY ; optional
        ld r2,-8(r12)
        add r2,r2,r12
        .localentry my_func, .-my_func

Add support for function prologue, along with gcc-5.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

kpatch-build/create-diff-object.c

@@ -2253,6 +2253,27 @@ static void kpatch_create_intermediate_sections(struct kpatch_elf *kelf,
 			 */
 			sym_objname = objname;
 
+			/*
+			 * function prologue generated by gcc6 on ppc64le has
+			 * the sequence:
+			 *
+			 *	.globl my_func
+			 *	.type my_func, @function
+			 *	.quad .TOC.-my_func
+			 * my_func:
+			 *	.reloc ., R_PPC64_ENTRY ; optional
+			 *	ld r2,-8(r12)
+			 *	add r2,r2,r12
+			 * 	.localentry my_func, .-my_func
+			 *
+			 * first entry past function global entry point is optional
+			 * and has the relocation type R_PPC64_ENTRY. We should *not*
+			 * skip this entry while building up the rela list, rather
+			 * skip it's lookup.
+			 */
+			if (rela->type == R_PPC64_ENTRY)
+				continue;
+
 			if (rela->sym->bind == STB_LOCAL) {
 				/* An unchanged local symbol */
 				ret = lookup_local_symbol(table,

kpatch-build/create-klp-module.c

@@ -243,7 +243,19 @@ static void create_klp_relasecs_and_syms(struct kpatch_elf *kelf, struct section
 			rela->offset = toc_offset;
 		else
 			rela->offset = krelas[index].offset;
-		rela->addend = krelas[index].addend;
+
+		/*
+		 * gcc6 adds offset for 0x8 for every local function entry in
+		 * .toc section, for avoiding setup of toc but when the previously
+		 * local function becomes global, toc is anyways setup. So remove
+		 * the wrong addend.
+		 */
+		if (!strcmp(base->name, ".toc") &&
+			rela->sym->type == STT_FUNC && rela->sym->bind == STB_LOCAL) {
+				rela->addend = 0;
+		} else {
+			rela->addend = krelas[index].addend;
+		}
 	}
 }
 

kpatch-build/kpatch-elf.c

@@ -76,6 +76,50 @@ int is_debug_section(struct section *sec)
 	       !strncmp(name, ".eh_frame", 9);
 }
 
+#ifdef __powerpc__
+
+/* Symbol st_others value for powerpc */
+#define STO_PPC64_LOCAL_BIT     5
+#define STO_PPC64_LOCAL_MASK    (7 << STO_PPC64_LOCAL_BIT)
+#define PPC64_LOCAL_ENTRY_OFFSET(other)                                 \
+	        (((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2) << 2)
+
+/*
+ * function prologue generated by gcc6 on ppc64le has
+ * the sequence:
+ *
+ *	.globl my_func
+ *	.type my_func, @function
+ *	.quad .TOC.-my_func
+ * my_func:
+ *	.reloc ., R_PPC64_ENTRY ; optional
+ *	ld r2,-8(r12)
+ *	add r2,r2,r12
+ * 	.localentry my_func, .-my_func
+ *
+ * my_func is resolved by .TOC.-my_func to a 64-bit offset stored
+ * above the global entry point. my_func st_value is set 0x8, for
+ * calling into the .localentry of the function.
+ *
+ * Number of instructions between global and local entry point of a
+ * function is mostly 8 instructions. i.e st_other == 3. The count of
+ * instruction can be decoded only for local function symbols.
+ */
+static int is_localentry_sym(struct symbol *sym)
+{
+	if (sym->type != STT_FUNC || sym->sym.st_shndx == SHN_UNDEF)
+		return 0;
+
+	if (sym->sym.st_value != 0x8)
+		return 0;
+
+	if (!PPC64_LOCAL_ENTRY_OFFSET(sym->sym.st_other))
+		return 0;
+
+	return 1;
+}
+#endif
+
 struct section *find_section_by_index(struct list_head *list, unsigned int index)
 {
 	struct section *sec;
@@ -328,9 +372,14 @@ void kpatch_create_symbol_list(struct kpatch_elf *kelf)
 					sym->name);
 
 			if (is_bundleable(sym)) {
-				if (sym->sym.st_value != 0)
+				if (sym->sym.st_value != 0) {
+#ifdef __powerpc__
+					if (!is_localentry_sym(sym))
+#endif
 					ERROR("symbol %s at offset %lu within section %s, expected 0",
-					      sym->name, sym->sym.st_value, sym->sec->name);
+						sym->name, sym->sym.st_value, sym->sec->name);
+				}
+
 				sym->sec->sym = sym;
 			} else if (sym->type == STT_SECTION) {
 				sym->sec->secsym = sym;

kpatch-build/kpatch-elf.h

@@ -131,6 +131,10 @@ struct rela *find_rela_by_offset(struct section *relasec, unsigned int offset);
 
 int offset_of_string(struct list_head *list, char *name);
 
+#ifndef R_PPC64_ENTRY
+#define R_PPC64_ENTRY   118
+#endif
+
 /*************
  * Functions
  * **********/