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 <linted@users.noreply.github.com>

2 files changed, 48 insertions, 0 deletions

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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <link.h>
+#include <elf.h>
+#include <dl-elf.h>
+
+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;
+}