[PATCH v3] Static PIE support for mips - devel

2 Sep 2022

Hello,
This is a slight update to the v2 patch. I realized that I left some
extraneous comments in crt1.S. This patch removes those comments.
--------
From f5a4f77a396631bfceea2967b6a9100b09802f6c Mon Sep 17 00:00:00 2001
From: linted linted@users.noreply.github.com
Date: Sat, 20 Aug 2022 16:41:38 -0400
Subject: [PATCH] Added support for creation of Static Position-Independent
 Executables (PIE) on mips
Updated config to allow compilation of rcrt1.o for mips and modified it's
crt1.S to perform relocates in __start.
The mips architecture performs relocations differently then most other
architectures. reloc_static_pie was rewritten, taking code from
dl-startup.c, in order to perfrom the additional relocations. Modifications
were made to mips' dl-startup.h to allow for the use of contained macros
without including _start definition.
Signed-off-by: linted linted@users.noreply.github.com
---
 extra/Configs/Config.in                |  2 +-
 ldso/ldso/mips/dl-startup.h            |  3 +-
 libc/misc/internals/Makefile.in        |  2 +-
 libc/misc/internals/reloc_static_pie.c | 93 +++++++++++++++++++++-----
 libc/sysdeps/linux/mips/crt1.S         | 23 +++++++
 5 files changed, 105 insertions(+), 18 deletions(-)

diff --git a/extra/Configs/Config.in b/extra/Configs/Config.in
index e0905e956..43c04fd0a 100644
--- a/extra/Configs/Config.in
+++ b/extra/Configs/Config.in
@@ -324,7 +324,7 @@ config DOPIC
 config STATIC_PIE
  bool "Add support for Static Position Independent Executables (PIE)"
  default n
- depends on DOPIC && !UCLIBC_FORMAT_FDPIC_ELF && (TARGET_arm ||
TARGET_i386 || TARGET_x86_64 || TARGET_aarch64)
+ depends on DOPIC && !UCLIBC_FORMAT_FDPIC_ELF && (TARGET_arm ||
TARGET_i386 || TARGET_x86_64 || TARGET_aarch64 || TARGET_mips)
config ARCH_HAS_NO_SHARED
  bool
diff --git a/ldso/ldso/mips/dl-startup.h b/ldso/ldso/mips/dl-startup.h
index 8026f1702..c2168d774 100644
--- a/ldso/ldso/mips/dl-startup.h
+++ b/ldso/ldso/mips/dl-startup.h
@@ -7,6 +7,7 @@
#include <sgidefs.h>
+#ifndef L_rcrt1
 __asm__(""
     " .text\n"
     " .globl _start\n"
@@ -114,6 +115,7 @@ __asm__(""
     "\n\n"
     ".previous\n"
 );
+#endif
/*
  * Get a pointer to the argv array.  On many platforms this can be just
@@ -191,6 +193,5 @@ do { \
  case R_MIPS_NONE: \
  break; \
  default: \
- SEND_STDERR("Aiieeee!"); \
  _dl_exit(1); \
  }
diff --git a/libc/misc/internals/Makefile.in
b/libc/misc/internals/Makefile.in
index 69af8b76e..908b18321 100644
--- a/libc/misc/internals/Makefile.in
+++ b/libc/misc/internals/Makefile.in
@@ -17,7 +17,7 @@ MISC_INTERNALS_SRC := $(patsubst
%.c,$(MISC_INTERNALS_DIR)/%.c,$(CSRC-y))
 MISC_INTERNALS_OBJ := $(patsubst %.c,$(MISC_INTERNALS_OUT)/%.o,$(CSRC-y))
CFLAGS-__uClibc_main.c := $(SSP_DISABLE_FLAGS)
-CFLAGS-reloc_static_pie.c := $(SSP_DISABLE_FLAGS)
+CFLAGS-reloc_static_pie.c := $(SSP_DISABLE_FLAGS) -DL_rcrt1
libc-y += $(MISC_INTERNALS_OBJ)
 ifneq ($(UCLIBC_FORMAT_SHARED_FLAT),y)
diff --git a/libc/misc/internals/reloc_static_pie.c
b/libc/misc/internals/reloc_static_pie.c
index 578202d23..c0027de6f 100644
--- a/libc/misc/internals/reloc_static_pie.c
+++ b/libc/misc/internals/reloc_static_pie.c
@@ -15,33 +15,96 @@
    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/.  */
-
+#define IS_IN_rtld      // force inline function calls
 #include <link.h>
 #include <elf.h>
 #include <dl-elf.h>
+#include <ldso.h>
+#ifdef __mips__
+#include <dl-startup.h>
+#endif
+
 ElfW(Addr) _dl_load_base = NULL;
void
 reloc_static_pie (ElfW(Addr) load_addr);
void
-reloc_static_pie (ElfW(Addr) load_addr)
+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};
+    int indx;
+    ElfW(Addr) got;
+    ElfW(Dyn) *dpnt;
+    struct elf_resolve tpnt_tmp;
+ struct elf_resolve *tpnt = &tpnt_tmp;
+
+    DL_BOOT_COMPUTE_GOT(got);
+    DL_BOOT_COMPUTE_DYN(dpnt, got, (DL_LOADADDR_TYPE)load_addr);
+
+    _dl_memset(tpnt, 0, sizeof(struct elf_resolve));
+    tpnt->loadaddr = load_addr;
+    tpnt->dynamic_addr = dpnt;
+
+    __dl_parse_dynamic_info(dpnt, tpnt->dynamic_info, NULL, load_addr);
+
+#if defined(PERFORM_BOOTSTRAP_GOT)
+ /* some arches (like MIPS) we have to tweak the GOT before relocations */
+ PERFORM_BOOTSTRAP_GOT(tpnt);
+#endif
+
+
+#if defined(ELF_MACHINE_PLTREL_OVERLAP)
+# define INDX_MAX 1
+#else
+# define INDX_MAX 2
+#endif
+
+    for (indx = 0; indx < INDX_MAX; indx++) {
+        unsigned long rel_addr, rel_size;
+        ElfW(Word) relative_count = tpnt->dynamic_info[DT_RELCONT_IDX];
+
+        rel_addr = (indx ? tpnt->dynamic_info[DT_JMPREL] :
+                           tpnt->dynamic_info[DT_RELOC_TABLE_ADDR]);
+        rel_size = (indx ? tpnt->dynamic_info[DT_PLTRELSZ] :
+               tpnt->dynamic_info[DT_RELOC_TABLE_SIZE]);
+
+        if (!rel_addr)
+            continue;
-    /* Read our own dynamic section and fill in the info array.  */
-    dyn_addr = ((void *) load_addr + elf_machine_dynamic ());
+        if((0 == indx) && relative_count) {
+ rel_size -= relative_count * sizeof(ELF_RELOC);
+            elf_machine_relative(load_addr, rel_addr, relative_count);
+ rel_addr += relative_count * sizeof(ELF_RELOC);
+        }
-    /* Use the underlying function to avoid TLS access before
initialization */
-    __dl_parse_dynamic_info(dyn_addr, dynamic_info, NULL, load_addr);
+#ifdef ARCH_NEEDS_BOOTSTRAP_RELOCS
+ {
+ ELF_RELOC *rpnt;
+ unsigned int i;
+ ElfW(Sym) *sym;
+ unsigned long symbol_addr;
+ int symtab_index;
+ unsigned long *reloc_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);
+ /* Now parse the relocation information */
+ rpnt = (ELF_RELOC *) rel_addr;
+ for (i = 0; i < rel_size; i += sizeof(ELF_RELOC), rpnt++) {
+ reloc_addr = (unsigned long *) DL_RELOC_ADDR(load_addr, (unsigned
long)rpnt->r_offset);
+ symtab_index = ELF_R_SYM(rpnt->r_info);
+ symbol_addr = 0;
+ sym = NULL;
+ if (symtab_index) {
+ ElfW(Sym) *symtab;
+ symtab = (ElfW(Sym) *) tpnt->dynamic_info[DT_SYMTAB];
+ sym = &symtab[symtab_index];
+ symbol_addr = (unsigned long) DL_RELOC_ADDR(load_addr, sym->st_value);
+ }
+ /* Use this machine-specific macro to perform the actual relocation.  */
+ PERFORM_BOOTSTRAP_RELOC(rpnt, reloc_addr, symbol_addr, load_addr, sym);
+ }
+ }
+#endif
+    }
     _dl_load_base = load_addr;
-}
+}
\ No newline at end of file
diff --git a/libc/sysdeps/linux/mips/crt1.S b/libc/sysdeps/linux/mips/crt1.S
index 083615515..7c4db447c 100644
--- a/libc/sysdeps/linux/mips/crt1.S
+++ b/libc/sysdeps/linux/mips/crt1.S
@@ -77,6 +77,10 @@
 #ifndef __UCLIBC_CTOR_DTOR__
  .weak _init
  .weak _fini
+#endif
+#ifdef L_rcrt1
+ .type reloc_static_pie,@function
+ .hidden .L0
 #endif
  .type    main,@function
  .type    __uClibc_main,@function
@@ -89,6 +93,25 @@ __start:
 #else
  PTR_LA $28, _gp             /* Setup GP correctly if we're non-PIC.  */
  move $31, $0
+#endif
+#ifdef L_rcrt1
+ PTR_LA $4, _DYNAMIC           /* Place _DYNAMIC into the GOT */
+ REG_S $4, -0x7ff0($28)        /* offset to GOT stolen from dl-startup */
+ jal .L0                       /* Get the current $pc address */
+.L0:
+ PTR_SUBU $4, $31, $25         /* Calculate load addr */
+ move $31, $0                  /* Clear ra */
+ and $29, -2 * SZREG           /* Ensure stack is aligned */
+ PTR_ADDIU $29, (-2 * SZREG)   /* Allocate 2 register spaces on stack */
+ REG_S $2, SZREG($29)          /* Store atexit in case it exists */
+ PTR_LA $5, reloc_static_pie   /* function calls before relocation
+                                 don't work unless we set $t9 manually */
+ PTR_ADDU $25, $4, $5          /* store reloc_static_pie in $t9 */
+ jalr $25                      /* call reloc_static_pie */
+ nop  /* delay slot, just in case */
+ REG_L $2, SZREG($29)          /* cleanup stack */
+ PTR_ADDIU $29, $29, (2 * SZREG)
+
 #endif
PTR_LA $4, main /* main */
-- 
2.34.1



    