powerpc/vdso: Disable building the 32-bit VDSO on little endian

The only little endian configuration we support is ppc64le. As such if
we're building little endian we don't need a 32-bit VDSO, because there
is no 32-bit userspace.

This patch is a fairly ugly mess of #ifdefs, but is the minimal logic
required to disable the 32-bit VDSO. We can hopefully clean up the
result in future with some further refactoring.

Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/kernel/Makefile

···
 				   signal.o sysfs.o cacheinfo.o time.o \
 				   prom.o traps.o setup-common.o \
 				   udbg.o misc.o io.o dma.o \
-				   misc_$(CONFIG_WORD_SIZE).o vdso32/ \
+				   misc_$(CONFIG_WORD_SIZE).o \
 				   of_platform.o prom_parse.o
 obj-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
 				   signal_64.o ptrace32.o \
 				   paca.o nvram_64.o firmware.o
+obj-$(CONFIG_VDSO32)		+= vdso32/
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_ppc970.o cpu_setup_pa6t.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_power.o

arch/powerpc/kernel/vdso.c

···
 /* The alignment of the vDSO */
 #define VDSO_ALIGNMENT	(1 << 16)
 
-extern char vdso32_start, vdso32_end;
-static void *vdso32_kbase = &vdso32_start;
 static unsigned int vdso32_pages;
+static void *vdso32_kbase;
 static struct page **vdso32_pagelist;
 unsigned long vdso32_sigtramp;
 unsigned long vdso32_rt_sigtramp;
+
+#ifdef CONFIG_VDSO32
+extern char vdso32_start, vdso32_end;
+#endif
 
 #ifdef CONFIG_PPC64
 extern char vdso64_start, vdso64_end;
···
 
 
 
+#ifdef CONFIG_VDSO32
 static void * __init find_section32(Elf32_Ehdr *ehdr, const char *secname,
 				  unsigned long *size)
 {
···
 
 	return 0;
 }
+#else /* !CONFIG_VDSO32 */
+static unsigned long __init find_function32(struct lib32_elfinfo *lib,
+					    const char *symname)
+{
+	return 0;
+}
+
+static int __init vdso_do_func_patch32(struct lib32_elfinfo *v32,
+				       struct lib64_elfinfo *v64,
+				       const char *orig, const char *fix)
+{
+	return 0;
+}
+#endif /* CONFIG_VDSO32 */
 
 
 #ifdef CONFIG_PPC64
···
 	 * Locate symbol tables & text section
 	 */
 
+#ifdef CONFIG_VDSO32
 	v32->dynsym = find_section32(v32->hdr, ".dynsym", &v32->dynsymsize);
 	v32->dynstr = find_section32(v32->hdr, ".dynstr", NULL);
 	if (v32->dynsym == NULL || v32->dynstr == NULL) {
···
 		return -1;
 	}
 	v32->text = sect - vdso32_kbase;
+#endif
 
 #ifdef CONFIG_PPC64
 	v64->dynsym = find_section64(v64->hdr, ".dynsym", &v64->dynsymsize);
···
 static __init int vdso_fixup_datapage(struct lib32_elfinfo *v32,
 				       struct lib64_elfinfo *v64)
 {
+#ifdef CONFIG_VDSO32
 	Elf32_Sym *sym32;
+#endif
 #ifdef CONFIG_PPC64
 	Elf64_Sym *sym64;
 
···
 		(sym64->st_value - VDSO64_LBASE);
 #endif /* CONFIG_PPC64 */
 
+#ifdef CONFIG_VDSO32
 	sym32 = find_symbol32(v32, "__kernel_datapage_offset");
 	if (sym32 == NULL) {
 		printk(KERN_ERR "vDSO32: Can't find symbol "
···
 	*((int *)(vdso32_kbase + (sym32->st_value - VDSO32_LBASE))) =
 		(vdso32_pages << PAGE_SHIFT) -
 		(sym32->st_value - VDSO32_LBASE);
+#endif
 
 	return 0;
 }
···
 				 start, start + size);
 #endif /* CONFIG_PPC64 */
 
+#ifdef CONFIG_VDSO32
 	start = find_section32(v32->hdr, "__ftr_fixup", &size);
 	if (start)
 		do_feature_fixups(cur_cpu_spec->cpu_features,
···
 	if (start)
 		do_lwsync_fixups(cur_cpu_spec->cpu_features,
 				 start, start + size);
+#endif
 
 	return 0;
 }
···
 #endif /* CONFIG_PPC64 */
 
 
+#ifdef CONFIG_VDSO32
+	vdso32_kbase = &vdso32_start;
+
 	/*
 	 * Calculate the size of the 32 bits vDSO
 	 */
 	vdso32_pages = (&vdso32_end - &vdso32_start) >> PAGE_SHIFT;
 	DBG("vdso32_kbase: %p, 0x%x pages\n", vdso32_kbase, vdso32_pages);
+#endif
 
 
 	/*
···
 		return 0;
 	}
 
+#ifdef CONFIG_VDSO32
 	/* Make sure pages are in the correct state */
 	vdso32_pagelist = kzalloc(sizeof(struct page *) * (vdso32_pages + 2),
 				  GFP_KERNEL);
···
 	}
 	vdso32_pagelist[i++] = virt_to_page(vdso_data);
 	vdso32_pagelist[i] = NULL;
+#endif
 
 #ifdef CONFIG_PPC64
 	vdso64_pagelist = kzalloc(sizeof(struct page *) * (vdso64_pages + 2),

arch/powerpc/platforms/Kconfig.cputype

···
 
 endmenu
 
+config VDSO32
+	def_bool y
+	depends on PPC32 || CPU_BIG_ENDIAN
+	help
+	  This symbol controls whether we build the 32-bit VDSO. We obviously
+	  want to do that if we're building a 32-bit kernel. If we're building
+	  a 64-bit kernel then we only want a 32-bit VDSO if we're building for
+	  big endian. That is because the only little endian configuration we
+	  support is ppc64le which is 64-bit only.
+
 choice
 	prompt "Endianness selection"
 	default CPU_BIG_ENDIAN