x86/vdso: Hack to keep 64-bit Go programs working (e0bf7b86) · Commits · 戴 / test

arch/x86/vdso/Makefile

+10 −8

Original line number	Diff line number	Diff line
		@@ -15,12 +15,8 @@ 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 +30,7 @@ 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 +100,13 @@ 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.

arch/x86/vdso/vdso-fakesections.c

0 → 100644

+32 −0

Original line number	Diff line number	Diff line
		/*
		* 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),
		}
		};

arch/x86/vdso/vdso2c.h

+18 −5

Original line number	Diff line number	Diff line
		@@ -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 = SHN_UNDEF; /* SHN_UNDEF == 0 */
		/* 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);

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