[uclibc-ng-devel] Static PIE support for mips

Hello,
I have completed a patch to get static pie support working for the mips
architecture.

Unfortunately a lot of the optimizations I made for previous architectures
needed to be rewritten in order to support the way that mips works. There
is a substantial rewrite of reloc_static_pie, however the code is nearly a
copy paste from dl-startup.c and has been tested with all the currently
supported architectures to ensure that it still works.

In order to compile with gcc, a patch for mips static pie is required. I'm
actively working on submitting said patch, but I do not have a link for it
yet. In the meantime, compilation using the following flags passed to gcc
should suffice.

mips-linux-gcc -static-pie -Bstatic -pie --no-dynamic-linker -z text
input.c -o output

----
From a6fa331c7ea16b5146c0d3ba3b2d6d723f09a9b4 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 perform 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 | 91 ++++++++++++++++++++++----
 libc/sysdeps/linux/mips/crt1.S         | 22 +++++++
 5 files changed, 103 insertions(+), 17 deletions(-)

Gave this patch a go with patched gcc for -static-pie for mips.

It works when compiling hello.c, but when I tried c++ hello.cpp program 
I get the following build error.

mipsel-linux-g++ -s -static-pie hello.cpp -o hello
/opt/tomatoware/mipsel-soft-mmc/mipsel-tomatoware-linux-uclibc/sysroot/usr/lib/rcrt1.o: 
in function `L0':
(.text+0x50): relocation truncated to fit: R_MIPS_PC16 against 
`reloc_static_pie'
collect2: error: ld returned 1 exit status

Also tested arm with the new reworked patch and it seems to work for c 
and c++ hello world.

Lance

On 8/20/2022 10:32 PM, linted wrote:
> Hello,
> I have completed a patch to get static pie support working for the 
> mips architecture.
>
> Unfortunately a lot of the optimizations I made for previous 
> architectures needed to be rewritten in order to support the way that 
> mips works. There is a substantial rewrite of reloc_static_pie, 
> however the code is nearly a copy paste from dl-startup.c and has been 
> tested with all the currently supported architectures to ensure that 
> it still works.
>
> In order to compile with gcc, a patch for mips static pie is required. 
> I'm actively working on submitting said patch, but I do not have a 
> link for it yet. In the meantime, compilation using the following 
> flags passed to gcc should suffice.
>
> mips-linux-gcc -static-pie -Bstatic -pie --no-dynamic-linker -z text 
> input.c -o output
>
> ----
> From a6fa331c7ea16b5146c0d3ba3b2d6d723f09a9b4 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 perform 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 | 91 ++++++++++++++++++++++----
>  libc/sysdeps/linux/mips/crt1.S         | 22 +++++++
>  5 files changed, 103 insertions(+), 17 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..cd9190d60 100644
> --- a/libc/misc/internals/reloc_static_pie.c
> +++ b/libc/misc/internals/reloc_static_pie.c
> @@ -20,28 +20,91 @@
>  #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..a7f72a90f 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
> + .weak reloc_static_pie
>  #endif
>   .type    main,@function
>   .type    __uClibc_main,@function
> @@ -90,6 +94,24 @@ __start:
>   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)
> + jal L0                        /* Get the current $pc address */
> +L0:
> + INT_SUB $25, $31, $25         /* Calculate load addr */
> + move $4, $25                  /* store load addr in param 1 */
> + and $29, -2 * SZREG           /* Ensure stack is aligned */
> + addi $29, $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 */
> + INT_ADDU $25, $25, $5         /* store reloc_static_pie in $t9 */
> + bal reloc_static_pie          /* call, and pray the compiler adds a nop
> +                                 in delay slot */
> + REG_L $2, SZREG($29)          /* cleanup stack */
> + addi $29, $29, (2 * SZREG)
> +#endif
>
>   PTR_LA $4, main /* main */
>   PTR_L $5, 0($29) /* argc */
> -- 
> 2.34.1
>
>
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