diff options
author | linted <linted@users.noreply.github.com> | 2022-07-23 16:25:41 -0400 |
---|---|---|
committer | Waldemar Brodkorb <wbx@openadk.org> | 2022-07-26 09:56:03 +0200 |
commit | 2c58afdb3ae6f900583cf7264cba6ab8a797e3e2 (patch) | |
tree | abb641e31fcab71a4e78905fd0124ca8b9a25eae /libc/sysdeps/linux | |
parent | 01961b12bc71d6eb4d9bda3632d73bb6764b8e85 (diff) |
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>
Diffstat (limited to 'libc/sysdeps/linux')
-rw-r--r-- | libc/sysdeps/linux/arm/crt1.S | 19 | ||||
-rw-r--r-- | libc/sysdeps/linux/i386/crt1.S | 20 | ||||
-rw-r--r-- | libc/sysdeps/linux/x86_64/crt1.S | 16 |
3 files changed, 54 insertions, 1 deletions
diff --git a/libc/sysdeps/linux/arm/crt1.S b/libc/sysdeps/linux/arm/crt1.S index a1d7f0f23..fade1d25c 100644 --- a/libc/sysdeps/linux/arm/crt1.S +++ b/libc/sysdeps/linux/arm/crt1.S @@ -246,6 +246,22 @@ _start: mov lr, #0 #ifdef __ARCH_USE_MMU__ +#ifdef L_rcrt1 + /* We don't need to save a1 since no dynamic linker should have run */ + ldr a1, .L_GOT /* Get value at .L_GOT + 0 (offset to GOT)*/ + adr a2, .L_GOT /* Get address of .L_GOT */ + ldr a3, .L_GOT+16 /* Get value of _start(GOT) stored in .L_GOT */ + adr a4, _start /* Get address of _start after relocation (changes to pc - ~30 or so) */ + add a1, a1, a2 /* Calculate where the GOT is */ + ldr a2, [a1, a3] /* GOT + _start(GOT) = offset of _start from begin of file */ + sub a1, a4, a2 /* Current addr of _start - offset from beginning of file = load addr */ + bl reloc_static_pie + mov a1, #0 /* Clean up a1 so that a random address won't get called at the end of program */ + + /* Clear the frame pointer and link register again since it might be modified by previous call */ + mov fp, #0 + mov lr, #0 +#endif /* Pop argc off the stack and save a pointer to argv */ ldr a2, [sp], #4 mov a3, sp @@ -309,6 +325,9 @@ _start: .word _fini(GOT) .word _init(GOT) .word main(GOT) +#ifdef L_rcrt1 + .word _start(GOT) +#endif #endif #endif diff --git a/libc/sysdeps/linux/i386/crt1.S b/libc/sysdeps/linux/i386/crt1.S index 35a6552e8..decc68967 100644 --- a/libc/sysdeps/linux/i386/crt1.S +++ b/libc/sysdeps/linux/i386/crt1.S @@ -67,6 +67,9 @@ #endif .type main,%function .type __uClibc_main,%function +#ifdef L_rcrt1 +.type reloc_static_pie,%function +#endif _start: /* Clear the frame pointer. The ABI suggests this be done, to mark the outermost frame obviously. */ @@ -100,6 +103,23 @@ _start: pop %ebx addl $_GLOBAL_OFFSET_TABLE_+[.-.L0],%ebx +#ifdef L_rcrt1 + /* We cannot rely on _DYNAMIC being usable here due to RELRO. + Instead we calculate the load address based off a symbol + that we know will exist, _start. */ + pushl %ecx /* Save ecx so it won't get clobbered */ + pushl %ebx /* Save ebx so it won't get clobbered */ + xorl %ecx, %ecx /* Clear ecx */ + addl _start@GOT(%ebx), %ecx /* Get the offset of _start */ + movl _start@GOT(%ebx), %eax /* Get the run time address of _start */ + subl %ecx, %eax /* Subtract to find the load address */ + pushl %eax /* Pass the load address */ + call reloc_static_pie@PLT + popl %eax /* Clean up from function call */ + popl %ebx /* Restore the GOT address */ + popl %ecx /* restore ecx */ +#endif + /* Push address of our own entry points to .fini and .init. */ pushl _fini@GOT(%ebx) pushl _init@GOT(%ebx) diff --git a/libc/sysdeps/linux/x86_64/crt1.S b/libc/sysdeps/linux/x86_64/crt1.S index 87777dd5d..701cbf2f6 100644 --- a/libc/sysdeps/linux/x86_64/crt1.S +++ b/libc/sysdeps/linux/x86_64/crt1.S @@ -80,6 +80,20 @@ _start: the outermost frame obviously. */ xorl %ebp, %ebp +#ifdef L_rcrt1 + pushq %rdi /* save rdi (but should be 0...) */ + pushq %rdx /* store rdx (rtld_fini) */ + xorq %rcx, %rcx /* ensure rcx is 0 */ + addq _start@GOTPCREL(%rip), %rcx /* get offset of _start from beginning of file */ + movq _start@GOTPCREL(%rip), %rax /* get run time address of _start */ + subq %rcx, %rax /* calculate run time load offset */ + movq %rax, %rdi /* load offset -> param 1 */ + call reloc_static_pie /* relocate dynamic addrs */ + xorq %rax, %rax /* cleanup */ + popq %rdx + popq %rdi +#endif + /* Extract the arguments as encoded on the stack and set up the arguments for __libc_start_main (int (*main) (int, char **, char **), int argc, char *argv, @@ -107,7 +121,7 @@ _start: which grow downwards). */ pushq %rsp -#if defined(L_Scrt1) +#if defined(L_Scrt1) || defined(L_rcrt1) /* Give address for main() */ movq main@GOTPCREL(%rip), %rdi |