[newlib-cygwin/main] Cygwin: aarch64: Add runtime pseudo relocation

[Jon Turney via Cygwin-cvs]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=ffa34d591ac978f87024b75f1873fead79e8a9f7

commit ffa34d591ac978f87024b75f1873fead79e8a9f7
Author: Evgeny Karpov <evg...@kmaps.co>
Date:   Tue Oct 28 09:46:29 2025 -0400

    Cygwin: aarch64: Add runtime pseudo relocation
    
    The patch adds runtime pseudo relocation handling for 12-bit and 21-bit
    relocations. The 26-bit relocation is handled using a jump stub generated by
    the linker.

Diff:
---
 winsup/cygwin/pseudo-reloc.cc | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/winsup/cygwin/pseudo-reloc.cc b/winsup/cygwin/pseudo-reloc.cc
index 5a0eab936..e24a90620 100644
--- a/winsup/cygwin/pseudo-reloc.cc
+++ b/winsup/cygwin/pseudo-reloc.cc
@@ -199,6 +199,9 @@ do_pseudo_reloc (void * start, void * end, void * base)
   ptrdiff_t reloc_target = (ptrdiff_t) ((char *)end - (char*)start);
   runtime_pseudo_reloc_v2 *v2_hdr = (runtime_pseudo_reloc_v2 *) start;
   runtime_pseudo_reloc_item_v2 *r;
+#ifdef __aarch64__
+  uint32_t opcode;
+#endif
 
   /* A valid relocation list will contain at least one entry, and
    * one v1 data structure (the smallest one) requires two DWORDs.
@@ -307,6 +310,13 @@ do_pseudo_reloc (void * start, void * end, void * base)
          if ((reldata & 0x8000) != 0)
            reldata |= ~((ptrdiff_t) 0xffff);
          break;
+#ifdef __aarch64__
+       case 12:
+       case 21:
+         opcode = (*((unsigned int *) reloc_target));
+         reldata = 0;
+         break;
+#endif
        case 32:
          reldata = (ptrdiff_t) (*((unsigned int *)reloc_target));
 #if defined (__x86_64__) || defined (_WIN64)
@@ -339,6 +349,31 @@ do_pseudo_reloc (void * start, void * end, void * base)
        case 16:
          __write_memory ((void *) reloc_target, &reldata, 2);
          break;
+#ifdef __aarch64__
+       case 12:
+         /* Replace add Xn, Xn, :lo12:label with ldr Xn, [Xn, 
:lo12:__imp__func].
+            That loads the address of _func into Xn.  */
+         opcode = 0xf9400000 | (opcode & 0x3ff); // ldr
+         reldata = ((ptrdiff_t) base + r->sym) & ((1 &lt;&lt; 12) - 1);
+         reldata >>= 3;
+         opcode |= reldata &lt;&lt; 10;
+         __write_memory ((void *) reloc_target, &opcode, 4);
+         break;
+       case 21:
+         /* Replace adrp Xn, label with adrp Xn, __imp__func.  */
+         opcode &= 0x9f00001f;
+         reldata = (((ptrdiff_t) base + r->sym) >> 12)
+                   - (((ptrdiff_t) base + r->target) >> 12);
+         reldata &= (1 &lt;&lt; 21) - 1;
+         opcode |= (reldata & 3) &lt;&lt; 29;
+         reldata >>= 2;
+         opcode |= reldata &lt;&lt; 5;
+         __write_memory ((void *) reloc_target, &opcode, 4);
+         break;
+       /* A note regarding 26 bits relocation.
+          A single opcode is not sufficient for 26 bits relocation in dynamic 
linking.
+          The linker generates a jump stub instead.  */
+#endif
        case 32:
 #if defined (__CYGWIN__) && defined (__x86_64__)
          if (reldata > (ptrdiff_t) __INT32_MAX__