From bfad381c0d1e19cae8461e105d8d4387dd2a14fe Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 18 Jun 2014 15:59:48 -0700 Subject: x86/vdso: Improve the fake section headers Fully stripping the vDSO has other unfortunate side effects: - binutils is unable to find ELF notes without a SHT_NOTE section. - Even elfutils has trouble: it can find ELF notes without a section table at all, but if a section table is present, it won't look for PT_NOTE. - gdb wants section names to match between stripped DSOs and their symbols; otherwise it will corrupt symbol addresses. We're also breaking the rules: section 0 is supposed to be SHT_NULL. Fix these problems by building a better fake section table. While we're at it, we might as well let buggy Go versions keep working well by giving the SHT_DYNSYM entry the correct size. This is a bit unfortunate: it adds quite a bit of size to the vdso image. If/when binutils improves and the improved versions become widespread, it would be worth considering dropping most of this. Signed-off-by: Andy Lutomirski Link: http://lkml.kernel.org/r/0e546a5eeaafdf1840e6ee654a55c1e727c26663.1403129369.git.luto@amacapital.net Signed-off-by: H. Peter Anvin --- arch/x86/vdso/vdso-fakesections.c | 44 ++++++++++++++++----------------------- 1 file changed, 18 insertions(+), 26 deletions(-) (limited to 'arch/x86/vdso/vdso-fakesections.c') diff --git a/arch/x86/vdso/vdso-fakesections.c b/arch/x86/vdso/vdso-fakesections.c index cb8a8d72c24..56927a7e497 100644 --- a/arch/x86/vdso/vdso-fakesections.c +++ b/arch/x86/vdso/vdso-fakesections.c @@ -2,31 +2,23 @@ * 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 + * String table for loadable section headers. See vdso2c.h for why + * this exists. */ -#ifndef __x86_64__ -#error This hack is specific to the 64-bit vDSO -#endif - -#include - -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), - } -}; +const char fake_shstrtab[] __attribute__((section(".fake_shstrtab"))) = + ".hash\0" + ".dynsym\0" + ".dynstr\0" + ".gnu.version\0" + ".gnu.version_d\0" + ".dynamic\0" + ".rodata\0" + ".fake_shstrtab\0" /* Yay, self-referential code. */ + ".note\0" + ".data\0" + ".altinstructions\0" + ".altinstr_replacement\0" + ".eh_frame_hdr\0" + ".eh_frame\0" + ".text"; -- cgit v1.2.3-70-g09d2