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authorlinted <linted@users.noreply.github.com>2022-07-23 16:25:41 -0400
committerWaldemar Brodkorb <wbx@openadk.org>2022-07-26 09:56:03 +0200
commit2c58afdb3ae6f900583cf7264cba6ab8a797e3e2 (patch)
treeabb641e31fcab71a4e78905fd0124ca8b9a25eae /libc/sysdeps/linux
parent01961b12bc71d6eb4d9bda3632d73bb6764b8e85 (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.S19
-rw-r--r--libc/sysdeps/linux/i386/crt1.S20
-rw-r--r--libc/sysdeps/linux/x86_64/crt1.S16
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