From 2c58afdb3ae6f900583cf7264cba6ab8a797e3e2 Mon Sep 17 00:00:00 2001 From: linted Date: Sat, 23 Jul 2022 16:25:41 -0400 Subject: Added support for creation of Static Position-Independent Executables (PIE) on i386, x86_64, and arm. This patch adds the generation of rcrt1.o which is used by gcc when compiling with the --static-pie flag. rcrt1.o differs from crt1.o and Scrt1.o in that it the executable has a dynamic section but no relocations have been performed prior to _start being called. crt1.o assumes there to be no dynamic relocations, and Scrt1.o has all relocations performed prior to execution by lsdo. The new reloc_static_pie function handles parsing the dynamic section, and performing the relocations in a architecture agnostic method. It also sets _dl_load_base which is used when initalizing TLS to ensure loading from the proper location. This allows for easier porting of static-pie support to additional architectures as only modifications to crt1.S to find the load address are required. Signed-off-by: linted --- libc/misc/internals/Makefile.in | 1 + libc/misc/internals/reloc_static_pie.c | 47 ++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+) create mode 100644 libc/misc/internals/reloc_static_pie.c (limited to 'libc/misc') diff --git a/libc/misc/internals/Makefile.in b/libc/misc/internals/Makefile.in index a8e4e36f9..4a6e73d2d 100644 --- a/libc/misc/internals/Makefile.in +++ b/libc/misc/internals/Makefile.in @@ -34,6 +34,7 @@ libc-static-$(UCLIBC_FORMAT_FLAT_SEP_DATA) += \ libc-static-$(UCLIBC_FORMAT_SHARED_FLAT) += \ $(MISC_INTERNALS_OUT)/shared_flat_initfini.o \ $(MISC_INTERNALS_OUT)/shared_flat_add_library.o +libc-static-$(STATIC_PIE) += $(MISC_INTERNALS_OUT)/reloc_static_pie.o libc-shared-$(UCLIBC_FORMAT_SHARED_FLAT) += \ $(MISC_INTERNALS_OUT)/shared_flat_initfini.os \ $(MISC_INTERNALS_OUT)/shared_flat_add_library.os diff --git a/libc/misc/internals/reloc_static_pie.c b/libc/misc/internals/reloc_static_pie.c new file mode 100644 index 000000000..578202d23 --- /dev/null +++ b/libc/misc/internals/reloc_static_pie.c @@ -0,0 +1,47 @@ +/* Support for relocating static PIE. + Copyright (C) 2017-2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include + +ElfW(Addr) _dl_load_base = NULL; + +void +reloc_static_pie (ElfW(Addr) load_addr); + +void +reloc_static_pie (ElfW(Addr) load_addr) +{ + ElfW(Word) relative_count = 0; + ElfW(Addr) rel_addr = 0; + ElfW(Dyn) * dyn_addr = NULL; + unsigned long dynamic_info[DYNAMIC_SIZE] = {0}; + + /* Read our own dynamic section and fill in the info array. */ + dyn_addr = ((void *) load_addr + elf_machine_dynamic ()); + + /* Use the underlying function to avoid TLS access before initialization */ + __dl_parse_dynamic_info(dyn_addr, dynamic_info, NULL, load_addr); + + /* Perform relocations */ + relative_count = dynamic_info[DT_RELCONT_IDX]; + rel_addr = dynamic_info[DT_RELOC_TABLE_ADDR]; + elf_machine_relative(load_addr, rel_addr, relative_count); + _dl_load_base = load_addr; +} -- cgit v1.2.3