dynamic linker bootstrap overhaul

this overhaul further reduces the amount of arch-specific code needed
by the dynamic linker and removes a number of assumptions, including:

- that symbolic function references inside libc are bound at link time
  via the linker option -Bsymbolic-functions.

- that libc functions used by the dynamic linker do not require
  access to data symbols.

- that static/internal function calls and data accesses can be made
  without performing any relocations, or that arch-specific startup
  code handled any such relocations needed.

removing these assumptions paves the way for allowing libc.so itself
to be built with stack protector (among other things), and is achieved
by a three-stage bootstrap process:

1. relative relocations are processed with a flat function.
2. symbolic relocations are processed with no external calls/data.
3. main program and dependency libs are processed with a
   fully-functional libc/ldso.

reduction in arch-specific code is achived through the following:

- crt_arch.h, used for generating crt1.o, now provides the entry point
  for the dynamic linker too.

- asm is no longer responsible for skipping the beginning of argv[]
  when ldso is invoked as a command.

- the functionality previously provided by __reloc_self for heavily
  GOT-dependent RISC archs is now the arch-agnostic stage-1.

- arch-specific relocation type codes are mapped directly as macros
  rather than via an inline translation function/switch statement.

2 files changed, 21 insertions, 30 deletions

diff --git a/arch/aarch64/crt_arch.h b/arch/aarch64/crt_arch.h
index 32066881..3a4b321e 100644
--- a/arch/aarch64/crt_arch.h
+++ b/arch/aarch64/crt_arch.h
@@ -1,9 +1,14 @@
 __asm__(
-".global _start\n"
-".type _start,%function\n"
-"_start:\n"
+".global " START "\n"
+".type " START ",%function\n"
+START ":\n"
 "	mov x29, #0\n"
 "	mov x30, #0\n"
 "	mov x0, sp\n"
+".weak _DYNAMIC\n"
+".hidden _DYNAMIC\n"
+"	adrp x1, _DYNAMIC\n"
+"	add x1, x1, #:lo12:_DYNAMIC\n"
 "	and sp, x0, #-16\n"
-"	b __cstart\n");
+"	b " START "_c\n"
+);
diff --git a/arch/aarch64/reloc.h b/arch/aarch64/reloc.h
index e95ae9a8..1b0402bc 100644
--- a/arch/aarch64/reloc.h
+++ b/arch/aarch64/reloc.h
@@ -1,5 +1,3 @@
-#include <string.h>
-#include <elf.h>
 #include <endian.h>
 
 #if __BYTE_ORDER == __BIG_ENDIAN
@@ -14,27 +12,15 @@
 
 #define TPOFF_K 16
 
-static int remap_rel(int type)
-{
-	switch(type) {
-	case R_AARCH64_ABS64:
-		return REL_SYMBOLIC;
-	case R_AARCH64_GLOB_DAT:
-		return REL_GOT;
-	case R_AARCH64_JUMP_SLOT:
-		return REL_PLT;
-	case R_AARCH64_RELATIVE:
-		return REL_RELATIVE;
-	case R_AARCH64_COPY:
-		return REL_COPY;
-	case R_AARCH64_TLS_DTPMOD64:
-		return REL_DTPMOD;
-	case R_AARCH64_TLS_DTPREL64:
-		return REL_DTPOFF;
-	case R_AARCH64_TLS_TPREL64:
-		return REL_TPOFF;
-	case R_AARCH64_TLSDESC:
-		return REL_TLSDESC;
-	}
-	return 0;
-}
+#define REL_SYMBOLIC    R_AARCH64_ABS64
+#define REL_GOT         R_AARCH64_GLOB_DAT
+#define REL_PLT         R_AARCH64_JUMP_SLOT
+#define REL_RELATIVE    R_AARCH64_RELATIVE
+#define REL_COPY        R_AARCH64_COPY
+#define REL_DTPMOD      R_AARCH64_TLS_DTPMOD64
+#define REL_DTPOFF      R_AARCH64_TLS_DTPREL64
+#define REL_TPOFF       R_AARCH64_TLS_TPREL64
+#define REL_TLSDESC     R_AARCH64_TLSDESC
+
+#define CRTJMP(pc,sp) __asm__ __volatile__( \
+	"mov sp,%1 ; bx %0" : : "r"(pc), "r"(sp) : "memory" )