x86: Support compiling out human-friendly processor feature names

The table mapping CPUID bits to human-readable strings takes up a
non-trivial amount of space, and only exists to support /proc/cpuinfo
and a couple of kernel messages.  Since programs depend on the format of
/proc/cpuinfo, force inclusion of the table when building with /proc
support; otherwise, support omitting that table to save space, in which
case the kernel messages will print features numerically instead.

In addition to saving 1408 bytes out of vmlinux, this also saves 1373
bytes out of the uncompressed setup code, which contributes directly to
the size of bzImage.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>

arch/x86/Kconfig

@@ -136,6 +136,7 @@ config X86
 	select HAVE_ACPI_APEI if ACPI
 	select HAVE_ACPI_APEI_NMI if ACPI
 	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
+	select X86_FEATURE_NAMES if PROC_FS
 
 config INSTRUCTION_DECODER
 	def_bool y
@@ -313,6 +314,17 @@ config SMP
 
 	  If you don't know what to do here, say N.
 
+config X86_FEATURE_NAMES
+	bool "Processor feature human-readable names" if EMBEDDED
+	default y
+	---help---
+	  This option compiles in a table of x86 feature bits and corresponding
+	  names.  This is required to support /proc/cpuinfo and a few kernel
+	  messages.  You can disable this to save space, at the expense of
+	  making those few kernel messages show numeric feature bits instead.
+
+	  If in doubt, say Y.
+
 config X86_X2APIC
 	bool "Support x2apic"
 	depends on X86_LOCAL_APIC && X86_64 && IRQ_REMAP

arch/x86/boot/Makefile

@@ -35,12 +35,14 @@ setup-y		+= video-vesa.o
 setup-y		+= video-bios.o
 
 targets		+= $(setup-y)
-hostprogs-y	:= mkcpustr tools/build
+hostprogs-y	:= tools/build
+hostprogs-$(CONFIG_X86_FEATURE_NAMES) += mkcpustr
 
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include \
 		    -include include/generated/autoconf.h \
 	            -D__EXPORTED_HEADERS__
 
+ifdef CONFIG_X86_FEATURE_NAMES
 $(obj)/cpu.o: $(obj)/cpustr.h
 
 quiet_cmd_cpustr = CPUSTR  $@
@@ -48,6 +50,7 @@ quiet_cmd_cpustr = CPUSTR  $@
 targets += cpustr.h
 $(obj)/cpustr.h: $(obj)/mkcpustr FORCE
 	$(call if_changed,cpustr)
+endif
 
 # ---------------------------------------------------------------------------
 

arch/x86/boot/cpu.c

@@ -16,7 +16,9 @@
  */
 
 #include "boot.h"
+#ifdef CONFIG_X86_FEATURE_NAMES
 #include "cpustr.h"
+#endif
 
 static char *cpu_name(int level)
 {
@@ -32,32 +34,13 @@ static char *cpu_name(int level)
 	}
 }
 
-int validate_cpu(void)
+static void show_cap_strs(u32 *err_flags)
 {
-	u32 *err_flags;
-	int cpu_level, req_level;
-	const unsigned char *msg_strs;
-
-	check_cpu(&cpu_level, &req_level, &err_flags);
-
-	if (cpu_level < req_level) {
-		printf("This kernel requires an %s CPU, ",
-		       cpu_name(req_level));
-		printf("but only detected an %s CPU.\n",
-		       cpu_name(cpu_level));
-		return -1;
-	}
-
-	if (err_flags) {
 	int i, j;
-		puts("This kernel requires the following features "
-		     "not present on the CPU:\n");
-
-		msg_strs = (const unsigned char *)x86_cap_strs;
-
+#ifdef CONFIG_X86_FEATURE_NAMES
+	const unsigned char *msg_strs = (const unsigned char *)x86_cap_strs;
 	for (i = 0; i < NCAPINTS; i++) {
 		u32 e = err_flags[i];
-
 		for (j = 0; j < 32; j++) {
 			if (msg_strs[0] < i ||
 			    (msg_strs[0] == i && msg_strs[1] < j)) {
@@ -77,6 +60,37 @@ int validate_cpu(void)
 			e >>= 1;
 		}
 	}
+#else
+	for (i = 0; i < NCAPINTS; i++) {
+		u32 e = err_flags[i];
+		for (j = 0; j < 32; j++) {
+			if (e & 1)
+				printf("%d:%d ", i, j);
+			e >>= 1;
+		}
+	}
+#endif
+}
+
+int validate_cpu(void)
+{
+	u32 *err_flags;
+	int cpu_level, req_level;
+
+	check_cpu(&cpu_level, &req_level, &err_flags);
+
+	if (cpu_level < req_level) {
+		printf("This kernel requires an %s CPU, ",
+		       cpu_name(req_level));
+		printf("but only detected an %s CPU.\n",
+		       cpu_name(cpu_level));
+		return -1;
+	}
+
+	if (err_flags) {
+		puts("This kernel requires the following features "
+		     "not present on the CPU:\n");
+		show_cap_strs(err_flags);
 		putchar('\n');
 		return -1;
 	} else {

arch/x86/include/asm/cpufeature.h

@@ -250,8 +250,15 @@
 #include <asm/asm.h>
 #include <linux/bitops.h>
 
+#ifdef CONFIG_X86_FEATURE_NAMES
 extern const char * const x86_cap_flags[NCAPINTS*32];
 extern const char * const x86_power_flags[32];
+#define X86_CAP_FMT "%s"
+#define x86_cap_flag(flag) x86_cap_flags[flag]
+#else
+#define X86_CAP_FMT "%d:%d"
+#define x86_cap_flag(flag) ((flag) >> 5), ((flag) & 31)
+#endif
 
 /*
  * In order to save room, we index into this array by doing

arch/x86/kernel/cpu/Makefile

@@ -13,11 +13,12 @@ nostackp := $(call cc-option, -fno-stack-protector)
 CFLAGS_common.o		:= $(nostackp)
 
 obj-y			:= intel_cacheinfo.o scattered.o topology.o
-obj-y			+= capflags.o powerflags.o common.o
+obj-y			+= common.o
 obj-y			+= rdrand.o
 obj-y			+= match.o
 
 obj-$(CONFIG_PROC_FS)	+= proc.o
+obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
 
 obj-$(CONFIG_X86_32)	+= bugs.o
 obj-$(CONFIG_X86_64)	+= bugs_64.o
@@ -50,6 +51,7 @@ obj-$(CONFIG_X86_LOCAL_APIC)		+= perfctr-watchdog.o perf_event_amd_ibs.o
 
 obj-$(CONFIG_HYPERVISOR_GUEST)		+= vmware.o hypervisor.o mshyperv.o
 
+ifdef CONFIG_X86_FEATURE_NAMES
 quiet_cmd_mkcapflags = MKCAP   $@
       cmd_mkcapflags = $(CONFIG_SHELL) $(srctree)/$(src)/mkcapflags.sh $< $@
 
@@ -58,3 +60,4 @@ cpufeature = $(src)/../../include/asm/cpufeature.h
 targets += capflags.c
 $(obj)/capflags.c: $(cpufeature) $(src)/mkcapflags.sh FORCE
 	$(call if_changed,mkcapflags)
+endif

arch/x86/kernel/cpu/common.c

@@ -346,8 +346,8 @@ static void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 			continue;
 
 		printk(KERN_WARNING
-		       "CPU: CPU feature %s disabled, no CPUID level 0x%x\n",
-				x86_cap_flags[df->feature], df->level);
+		       "CPU: CPU feature " X86_CAP_FMT " disabled, no CPUID level 0x%x\n",
+				x86_cap_flag(df->feature), df->level);
 	}
 }