[committed] libphobos: Push all callee-save registers on the stack before GC scan on ARM

[Iain Buclaw via Gcc-patches]

Hi,

This is the library fix for PR103520 that also prevents the garbage
collector from releasing live memory.  However this requires that the
host compiler has been patched with this fix, so the GC will remain
disabled in the D front-end for now until enough time has passed for
this to have trickled down into enough releases.

Bootstrapped and regression tested on aarch64-linux-gnu, committed to
mainline and backported to the release branches.

Regards,
Iain

---
libphobos/ChangeLog:

        * libdruntime/core/thread/osthread.d (callWithStackShell): Push all
        callee-save registers on the stack for AArch64 and ARM.
---
 libphobos/libdruntime/core/thread/osthread.d | 29 ++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/libphobos/libdruntime/core/thread/osthread.d 
b/libphobos/libdruntime/core/thread/osthread.d
index 653adb91a7d..c9bc1305ad0 100644
--- a/libphobos/libdruntime/core/thread/osthread.d
+++ b/libphobos/libdruntime/core/thread/osthread.d
@@ -1487,6 +1487,35 @@ in (fn)
             }}
             sp = cast(void*)&regs[0];
         }
+        else version (AArch64)
+        {
+            // Callee-save registers, x19-x28 according to AAPCS64, section
+            // 5.1.1.  Include x29 fp because it optionally can be a callee
+            // saved reg
+            size_t[11] regs = void;
+            // store the registers in pairs
+            asm pure nothrow @nogc
+            {
+                "stp x19, x20, %0" : "=m" (regs[ 0]), "=m" (regs[1]);
+                "stp x21, x22, %0" : "=m" (regs[ 2]), "=m" (regs[3]);
+                "stp x23, x24, %0" : "=m" (regs[ 4]), "=m" (regs[5]);
+                "stp x25, x26, %0" : "=m" (regs[ 6]), "=m" (regs[7]);
+                "stp x27, x28, %0" : "=m" (regs[ 8]), "=m" (regs[9]);
+                "str x29, %0"      : "=m" (regs[10]);
+                "mov %0, sp"       : "=r" (sp);
+            }
+        }
+        else version (ARM)
+        {
+            // Callee-save registers, according to AAPCS, section 5.1.1.
+            // arm and thumb2 instructions
+            size_t[8] regs = void;
+            asm pure nothrow @nogc
+            {
+                "stm %0, {r4-r11}" : : "r" (regs.ptr) : "memory";
+                "mov %0, sp"       : "=r" (sp);
+            }
+        }
         else
         {
             __builtin_unwind_init();
-- 
2.30.2