From patchwork series 502789

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=502789

Author: Fox Snowpatch

Makefile

@@ -1514,6 +1514,13 @@ ifdef CONFIG_OBJTOOL
 prepare: tools/objtool
 endif
 
+# CONFIG_OBJTOOL and CONFIG_HAVE_OBJTOOL_FTR_FIXUP are unrelated, separate
+# options. It was integrated in objtool in order to borrow the elf parser,
+# but this is different from how the other objtool commands are used.
+ifdef CONFIG_HAVE_OBJTOOL_FTR_FIXUP
+prepare: tools/objtool
+endif
+
 ifdef CONFIG_BPF
 ifdef CONFIG_DEBUG_INFO_BTF
 prepare: tools/bpf/resolve_btfids

arch/powerpc/Kconfig

@@ -23,6 +23,9 @@ config 64BIT
 	bool
 	default y if PPC64
 
+config HAVE_OBJTOOL_FTR_FIXUP
+        def_bool y
+
 config LIVEPATCH_64
 	def_bool PPC64
 	depends on LIVEPATCH

arch/powerpc/Makefile

@@ -105,6 +105,11 @@ LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie --no-dynamic-linker
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext
 LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
 
+# --emit-relocs required for post-link fixup of alternate feature
+# text section relocations.
+LDFLAGS_vmlinux        += --emit-relocs
+KBUILD_LDFLAGS_MODULE += --emit-relocs
+
 ifdef CONFIG_PPC64
 ifndef CONFIG_PPC_KERNEL_PCREL
 	# -mcmodel=medium breaks modules because it uses 32bit offsets from

arch/powerpc/include/asm/feature-fixups.h

@@ -32,7 +32,7 @@
 
 #define FTR_SECTION_ELSE_NESTED(label)			\
 label##2:						\
-	.pushsection __ftr_alt_##label,"a";		\
+	.pushsection __ftr_alt_##label, "ax";		\
 	.align 2;					\
 label##3:
 

arch/powerpc/kernel/vmlinux.lds.S

@@ -99,8 +99,8 @@ SECTIONS
 	.text : AT(ADDR(.text) - LOAD_OFFSET) {
 		ALIGN_FUNCTION();
 #endif
-		/* careful! __ftr_alt_* sections need to be close to .text */
-		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
+		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely
+			.text.unlikely.* .fixup .ref.text);
 		*(.tramp.ftrace.text);
 		NOINSTR_TEXT
 		SCHED_TEXT
@@ -267,6 +267,10 @@ SECTIONS
 		_einittext = .;
 	} :text
 
+	.__ftr_alternates.text : AT(ADDR(.__ftr_alternates.text) - LOAD_OFFSET) {
+		*(__ftr_alt*);
+	}
+
 	/* .exit.text is discarded at runtime, not link time,
 	 * to deal with references from __bug_table
 	 */

arch/powerpc/lib/feature-fixups.c

@@ -53,22 +53,10 @@ static u32 *calc_addr(struct fixup_entry *fcur, long offset)
 
 static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_end)
 {
-	int err;
 	ppc_inst_t instr;
 
 	instr = ppc_inst_read(src);
 
-	if (instr_is_relative_branch(ppc_inst_read(src))) {
-		u32 *target = (u32 *)branch_target(src);
-
-		/* Branch within the section doesn't need translating */
-		if (target < alt_start || target > alt_end) {
-			err = translate_branch(&instr, dest, src);
-			if (err)
-				return 1;
-		}
-	}
-
 	raw_patch_instruction(dest, instr);
 
 	return 0;

scripts/Makefile.lib

@@ -179,10 +179,10 @@ cpp_flags      = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 
 ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F))
 
-ifdef CONFIG_OBJTOOL
-
 objtool := $(objtree)/tools/objtool/objtool
 
+ifdef CONFIG_OBJTOOL
+
 objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
 objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake

scripts/Makefile.vmlinux

@@ -65,7 +65,8 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
 # Final link of vmlinux with optional arch pass after final link
 cmd_link_vmlinux =							\
 	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
-	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
+	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true);	\
+	$(if $(CONFIG_HAVE_OBJTOOL_FTR_FIXUP), $(objtool) --ftr-fixup --link $@, true)
 
 targets += vmlinux.unstripped .vmlinux.export.o
 vmlinux.unstripped: scripts/link-vmlinux.sh vmlinux.o .vmlinux.export.o $(KBUILD_LDS) FORCE
@@ -81,11 +82,15 @@ endif
 # vmlinux
 # ---------------------------------------------------------------------------
 
+# These configurations require vmlinux.unstripped to be linked with
+# '--emit-relocs', which need to be stripped from the final vmlinux.
+uses-emit-relocs := $(or $(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),$(CONFIG_HAVE_OBJTOOL_FTR_FIXUP))
+
 remove-section-y                                   := .modinfo
-remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*' '!.rel*.dyn'
+remove-section-$(uses-emit-relocs)                 += '.rel*' '!.rel*.dyn'
 # for compatibility with binutils < 2.32
 # https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c12d9fa2afe7abcbe407a00e15719e1a1350c2a7
-remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel.*'
+remove-section-$(uses-emit-relocs)                 += '.rel.*'
 
 remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*'
 

tools/objtool/arch/powerpc/decode.c

@@ -59,13 +59,26 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 	enum insn_type typ;
 	unsigned long imm;
 	u32 ins;
+	unsigned int aa;
 
 	ins = bswap_if_needed(file->elf, *(u32 *)(sec->data->d_buf + offset));
 	opcode = ins >> 26;
 	typ = INSN_OTHER;
 	imm = 0;
+	aa = ins & 2;
 
 	switch (opcode) {
+	case 16:
+		if (ins & 1)
+			typ = INSN_OTHER;
+		else
+			typ = INSN_JUMP_CONDITIONAL;
+		imm = ins & 0xfffc;
+		if (imm & 0x8000)
+			imm -= 0x10000;
+		insn->immediate = imm | aa;
+		break;
+
 	case 18: /* b[l][a] */
 		if (ins == 0x48000005)	/* bl .+4 */
 			typ = INSN_OTHER;
@@ -77,7 +90,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 		imm = ins & 0x3fffffc;
 		if (imm & 0x2000000)
 			imm -= 0x4000000;
-		imm |= ins & 2;	/* AA flag */
+		insn->immediate = imm | aa;
 		break;
 	}