summaryrefslogtreecommitdiff
path: root/libc/sysdeps/linux/arm/crt1.S
diff options
context:
space:
mode:
Diffstat (limited to 'libc/sysdeps/linux/arm/crt1.S')
-rw-r--r--libc/sysdeps/linux/arm/crt1.S161
1 files changed, 161 insertions, 0 deletions
diff --git a/libc/sysdeps/linux/arm/crt1.S b/libc/sysdeps/linux/arm/crt1.S
new file mode 100644
index 000000000..3bea01e73
--- /dev/null
+++ b/libc/sysdeps/linux/arm/crt1.S
@@ -0,0 +1,161 @@
+/* When we enter this piece of code, the program stack looks like this:
+ argc argument counter (integer)
+ argv[0] program name (pointer)
+ argv[1...N] program args (pointers)
+ argv[argc-1] end of args (integer)
+ NULL
+ env[0...N] environment variables (pointers)
+ NULL
+
+ For uClinux it looks like this:
+
+ argc argument counter (integer)
+ argv char *argv[]
+ envp char *envp[]
+ argv[0] program name (pointer)
+ argv[1...N] program args (pointers)
+ argv[argc-1] end of args (integer)
+ NULL
+ env[0...N] environment variables (pointers)
+ NULL
+
+ When we are done here, we want
+ a1=argc
+ a2=argv[0]
+ a3=argv[argc+1]
+
+ARM register quick reference:
+
+ Name Number ARM Procedure Calling Standard Role
+
+ a1 r0 argument 1 / integer result / scratch register / argc
+ a2 r1 argument 2 / scratch register / argv
+ a3 r2 argument 3 / scratch register / envp
+ a4 r3 argument 4 / scratch register
+ v1 r4 register variable
+ v2 r5 register variable
+ v3 r6 register variable
+ v4 r7 register variable
+ v5 r8 register variable
+ sb/v6 r9 static base / register variable
+ sl/v7 r10 stack limit / stack chunk handle / reg. variable
+ fp r11 frame pointer
+ ip r12 scratch register / new-sb in inter-link-unit calls
+ sp r13 lower end of current stack frame
+ lr r14 link address / scratch register
+ pc r15 program counter
+*/
+
+#include <features.h>
+
+.text
+ .global _start
+ .type _start,%function
+ .type _init,%function
+ .type _fini,%function
+ .type main,%function
+ .type __uClibc_main,%function
+
+
+.text
+_start:
+ /* clear the frame pointer */
+ mov fp, #0
+
+#ifdef __PIC__
+ /* Store the address of main in r0 */
+ adr r5, .L_main
+ ldr r0, .L_main
+ add r0, r0, r5
+
+#else
+ /* Store the address of main in r0 */
+ ldr r0, =main
+#endif
+
+#ifdef __ARCH_HAS_MMU__
+
+ /* Load register r1 (argc) from the stack to its final resting place */
+ ldr r1, [sp], #4
+
+ /* Copy argv pointer into r2 -- which its final resting place */
+ mov r2, sp
+#else
+ /*
+ * uClinux stacks look a little different from normal
+ * MMU-full Linux stacks (for no good reason)
+ */
+ /* pull argc, argv and envp off the stack */
+ ldr r1,[sp, #0]
+ ldr r2,[sp, #4]
+#endif
+
+#ifdef __PIC__
+ /* Store the address of _init in r3 */
+ adr r5, .L_init
+ ldr r3, .L_init
+ add r3, r3, r5
+
+ /* Push _fini onto the stack as an argument to main() */
+ ldr r4, .L_init + 4
+ add r4, r4, r5
+ stmfd sp!, {r4}
+
+ /* Push rtld_fini onto the stack as an argument to main() */
+ ldr r4, .L_init + 8
+ add r4, r4, r5
+ stmfd sp!, {r4}
+#else
+ /* Store the address of _init in r3 as an argument to main() */
+ ldr r3, =_init
+
+ /* Push _fini onto the stack as an argument to main() */
+ ldr r4, =_fini
+ stmfd sp!, {r4}
+
+ /* Push rtld_fini onto the stack as an argument to main() */
+ ldr r4, =rtld_fini
+ stmfd sp!, {r4}
+#endif
+
+ /* We need to call __uClibc_main which should not return.
+ __uClibc_main (int (*main) (int, char **, char **), int argc,
+ char **argv, void (*init) (void), void (*fini) (void),
+ void (*rtld_fini) (void), void *stack_end)
+ */
+ bl __uClibc_main
+
+ /* Crash if somehow `exit' returns anyways. */
+ bl abort
+
+#ifdef __PIC__
+.L_init:
+ .word _init
+ .word _fini
+ .word rtld_fini
+.L_main:
+ .word main
+#endif
+
+/* We need this stuff to make gdb behave itself, otherwise
+ gdb will choke with SIGILL when trying to debug apps.
+*/
+ .section ".note.ABI-tag", "a"
+ .align 4
+ .long 1f - 0f
+ .long 3f - 2f
+ .long 1
+0: .asciz "GNU"
+1: .align 4
+2: .long 0
+ .long 2,0,0
+3: .align 4
+
+/* Define a symbol for the first piece of initialized data. */
+ .data
+ .globl __data_start
+__data_start:
+ .long 0
+ .weak data_start
+ data_start = __data_start
+