Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 vdso fixes from Peter Anvin:
 "Fixes for x86/vdso.

  One is a simple build fix for bigendian hosts, one is to make "make
  vdso_install" work again, and the rest is about working around a bug
  in Google's Go language -- two are documentation patches that improves
  the sample code that the Go coders took, modified, and broke; the
  other two implements a workaround that keeps existing Go binaries from
  segfaulting at least"

* 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/vdso: Fix vdso_install
  x86/vdso: Hack to keep 64-bit Go programs working
  x86/vdso: Add PUT_LE to store little-endian values
  x86/vdso/doc: Make vDSO examples more portable
  x86/vdso/doc: Rename vdso_test.c to vdso_standalone_test_x86.c
  x86, vdso: Remove one final use of htole16()

4 files changed, 87 insertions, 27 deletions

diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index 9769df0..3c0809a 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -9,18 +9,9 @@ VDSOX32-$(CONFIG_X86_X32_ABI)	:= y
 VDSO32-$(CONFIG_X86_32)		:= y
 VDSO32-$(CONFIG_COMPAT)		:= y
 
-vdso-install-$(VDSO64-y)	+= vdso.so
-vdso-install-$(VDSOX32-y)	+= vdsox32.so
-vdso-install-$(VDSO32-y)	+= $(vdso32-images)
-
-
 # files to link into the vdso
-vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
-
-vobjs-$(VDSOX32-y) += $(vobjx32s-compat)
-
-# Filter out x32 objects.
-vobj64s := $(filter-out $(vobjx32s-compat),$(vobjs-y))
+vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vdso-fakesections.o
+vobjs-nox32 := vdso-fakesections.o
 
 # files to link into kernel
 obj-y				+= vma.o
@@ -34,7 +25,7 @@ vdso_img-$(VDSO32-y)		+= 32-sysenter
 
 obj-$(VDSO32-y)			+= vdso32-setup.o
 
-vobjs := $(foreach F,$(vobj64s),$(obj)/$F)
+vobjs := $(foreach F,$(vobjs-y),$(obj)/$F)
 
 $(obj)/vdso.o: $(obj)/vdso.so
 
@@ -104,7 +95,13 @@ VDSO_LDFLAGS_vdsox32.lds = -Wl,-m,elf32_x86_64 \
 			   -Wl,-z,max-page-size=4096 \
 			   -Wl,-z,common-page-size=4096
 
-vobjx32s-y := $(vobj64s:.o=-x32.o)
+# 64-bit objects to re-brand as x32
+vobjs64-for-x32 := $(filter-out $(vobjs-nox32),$(vobjs-y))
+
+# x32-rebranded versions
+vobjx32s-y := $(vobjs64-for-x32:.o=-x32.o)
+
+# same thing, but in the output directory
 vobjx32s := $(foreach F,$(vobjx32s-y),$(obj)/$F)
 
 # Convert 64bit object file to x32 for x32 vDSO.
@@ -176,15 +173,20 @@ VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) \
 GCOV_PROFILE := n
 
 #
-# Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
+# Install the unstripped copies of vdso*.so.
 #
-quiet_cmd_vdso_install = INSTALL $@
-      cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
-$(vdso-install-y): %.so: $(obj)/%.so.dbg FORCE
+quiet_cmd_vdso_install = INSTALL $(@:install_%=%)
+      cmd_vdso_install = cp $< $(MODLIB)/vdso/$(@:install_%=%)
+
+vdso_img_insttargets := $(vdso_img_sodbg:%.dbg=install_%)
+
+$(MODLIB)/vdso: FORCE
 	@mkdir -p $(MODLIB)/vdso
+
+$(vdso_img_insttargets): install_%: $(obj)/%.dbg $(MODLIB)/vdso FORCE
 	$(call cmd,vdso_install)
 
-PHONY += vdso_install $(vdso-install-y)
-vdso_install: $(vdso-install-y)
+PHONY += vdso_install $(vdso_img_insttargets)
+vdso_install: $(vdso_img_insttargets) FORCE
 
 clean-files := vdso32-syscall* vdso32-sysenter* vdso32-int80*
diff --git a/arch/x86/vdso/vdso-fakesections.c b/arch/x86/vdso/vdso-fakesections.c
new file mode 100644
index 0000000..cb8a8d7
--- /dev/null
+++ b/arch/x86/vdso/vdso-fakesections.c
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2014 Andy Lutomirski
+ * Subject to the GNU Public License, v.2
+ *
+ * Hack to keep broken Go programs working.
+ *
+ * The Go runtime had a couple of bugs: it would read the section table to try
+ * to figure out how many dynamic symbols there were (it shouldn't have looked
+ * at the section table at all) and, if there were no SHT_SYNDYM section table
+ * entry, it would use an uninitialized value for the number of symbols.  As a
+ * workaround, we supply a minimal section table.  vdso2c will adjust the
+ * in-memory image so that "vdso_fake_sections" becomes the section table.
+ *
+ * The bug was introduced by:
+ * https://code.google.com/p/go/source/detail?r=56ea40aac72b (2012-08-31)
+ * and is being addressed in the Go runtime in this issue:
+ * https://code.google.com/p/go/issues/detail?id=8197
+ */
+
+#ifndef __x86_64__
+#error This hack is specific to the 64-bit vDSO
+#endif
+
+#include <linux/elf.h>
+
+extern const __visible struct elf64_shdr vdso_fake_sections[];
+const __visible struct elf64_shdr vdso_fake_sections[] = {
+	{
+		.sh_type = SHT_DYNSYM,
+		.sh_entsize = sizeof(Elf64_Sym),
+	}
+};
diff --git a/arch/x86/vdso/vdso2c.c b/arch/x86/vdso/vdso2c.c
index 450ac6e..7a6bf50 100644
--- a/arch/x86/vdso/vdso2c.c
+++ b/arch/x86/vdso/vdso2c.c
@@ -54,7 +54,7 @@ static void fail(const char *format, ...)
 }
 
 /*
- * Evil macros to do a little-endian read.
+ * Evil macros for little-endian reads and writes
  */
 #define GLE(x, bits, ifnot)						\
 	__builtin_choose_expr(						\
@@ -62,11 +62,24 @@ static void fail(const char *format, ...)
 		(__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
 
 extern void bad_get_le(void);
-#define LAST_LE(x)							\
+#define LAST_GLE(x)							\
 	__builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
 
 #define GET_LE(x)							\
-	GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_LE(x))))
+	GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
+
+#define PLE(x, val, bits, ifnot)					\
+	__builtin_choose_expr(						\
+		(sizeof(*(x)) == bits/8),				\
+		put_unaligned_le##bits((val), (x)), ifnot)
+
+extern void bad_put_le(void);
+#define LAST_PLE(x, val)						\
+	__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
+
+#define PUT_LE(x, val)					\
+	PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
+
 
 #define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
 
diff --git a/arch/x86/vdso/vdso2c.h b/arch/x86/vdso/vdso2c.h
index 8a07463..c6eefaf 100644
--- a/arch/x86/vdso/vdso2c.h
+++ b/arch/x86/vdso/vdso2c.h
@@ -18,6 +18,8 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
 	const char *secstrings;
 	uint64_t syms[NSYMS] = {};
 
+	uint64_t fake_sections_value = 0, fake_sections_size = 0;
+
 	Elf_Phdr *pt = (Elf_Phdr *)(addr + GET_LE(&hdr->e_phoff));
 
 	/* Walk the segment table. */
@@ -84,6 +86,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
 			GET_LE(&symtab_hdr->sh_entsize) * i;
 		const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
 			GET_LE(&sym->st_name);
+
 		for (k = 0; k < NSYMS; k++) {
 			if (!strcmp(name, required_syms[k])) {
 				if (syms[k]) {
@@ -93,6 +96,13 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
 				syms[k] = GET_LE(&sym->st_value);
 			}
 		}
+
+		if (!strcmp(name, "vdso_fake_sections")) {
+			if (fake_sections_value)
+				fail("duplicate vdso_fake_sections\n");
+			fake_sections_value = GET_LE(&sym->st_value);
+			fake_sections_size = GET_LE(&sym->st_size);
+		}
 	}
 
 	/* Validate mapping addresses. */
@@ -112,11 +122,14 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
 	if (syms[sym_end_mapping] % 4096)
 		fail("end_mapping must be a multiple of 4096\n");
 
-	/* Remove sections. */
-	hdr->e_shoff = 0;
-	hdr->e_shentsize = 0;
-	hdr->e_shnum = 0;
-	hdr->e_shstrndx = htole16(SHN_UNDEF);
+	/* Remove sections or use fakes */
+	if (fake_sections_size % sizeof(Elf_Shdr))
+		fail("vdso_fake_sections size is not a multiple of %ld\n",
+		     (long)sizeof(Elf_Shdr));
+	PUT_LE(&hdr->e_shoff, fake_sections_value);
+	PUT_LE(&hdr->e_shentsize, fake_sections_value ? sizeof(Elf_Shdr) : 0);
+	PUT_LE(&hdr->e_shnum, fake_sections_size / sizeof(Elf_Shdr));
+	PUT_LE(&hdr->e_shstrndx, SHN_UNDEF);
 
 	if (!name) {
 		fwrite(addr, load_size, 1, outfile);