fix(proot-termux): LLVM 21 build and runtime fixes

- Cross-prefixed readelf for loader-info.c generation
- Loader ELF p_align binary patch (lld nmagic workaround)
- AArch64 SP alignment in transfer_load_script (align-sp.patch)

Author: mhuesch

modules/environment/login/default.nix

@@ -87,8 +87,8 @@ in
       prootStatic =
         let
           crossCompiledPaths = {
-            aarch64-linux = "/nix/store/w9km5x8v4xma2wgqxpsx4jbr2kz7nk33-proot-termux-static-aarch64-unknown-linux-android-0-unstable-2025-10-19";
-            x86_64-linux = "/nix/store/xpnf8vzswwaqmgxakcqhw8f5b4363rsh-proot-termux-static-x86_64-unknown-linux-android-0-unstable-2025-10-19";
+            aarch64-linux = "/nix/store/0xjhdhcarb47yhhlgbjna3qn0cwl7gxh-proot-termux-static-aarch64-unknown-linux-android-0-unstable-2025-10-19";
+            x86_64-linux = "/nix/store/qxnj7km4nqvk1fgbnb71afy9ma78c60i-proot-termux-static-x86_64-unknown-linux-android-0-unstable-2025-10-19";
           };
         in
         "${crossCompiledPaths.${targetSystem}}";

pkgs/proot-termux/align-sp.patch

@@ -0,0 +1,28 @@
+commit 89ea8886e69cb175eee727c871b2251f1fc7aea1
+Author: Alexander Sosedkin <monk@unboiled.info>
+Date:   Tue Feb 17 07:29:14 2026 +0100
+
+    Align SP to 16 bytes on AArch64
+    
+    Reported-by: Michael Hueschen <m@mhueschen.space>
+
+diff --git a/src/execve/exit.c b/src/execve/exit.c
+index f32d3ec..b12c574 100644
+--- a/src/execve/exit.c
++++ b/src/execve/exit.c
+@@ -224,9 +224,14 @@ static int transfer_load_script(Tracee *tracee)
+ 
+ 	/* A padding will be appended at the end of the load script
+ 	 * (a.k.a "strings area") to ensure this latter is aligned to
+-	 * a word boundary, for sake of performance.  */
++	 * a word boundary, for the sake of performance
++	 * (or 16 bytes since AArch64 needs SP to 16-bytes aligned). */
+ 	padding_size = (stack_pointer - string1_size - string2_size - string3_size)
++#ifdef ARCH_ARM64
++		        % 16;
++#else
+ 			% sizeof_word(tracee);
++#endif
+ 
+ 	strings_size = string1_size + string2_size + string3_size + padding_size;
+ 	string1_address = stack_pointer - strings_size;

pkgs/proot-termux/default.nix

@@ -34,8 +34,26 @@ stdenv.mkDerivation {
       '#define HAS_LOADER_32BIT true' \
       ""
     ! (grep -F '#define HAS_LOADER_32BIT' src/arch.h)
-    # don't wanna get a 128GB loader (LLVM 17->21 regression?)
+    # LLVM 21's lld sets file_offset = vaddr for -Ttext=0x2000000000,
+    # producing an 8 GB loader binary. Adding -n (nmagic) fixes the file
+    # size but sets p_align=4, which Android kernels reject (EINVAL on
+    # execve). Solution: link with -n, then binary-patch p_align to
+    # 0x10000 (64 KB, safe for 4/16/64 KB page-size devices).
     substituteInPlace src/GNUmakefile --replace ",-Ttext" ",-n,-Ttext"
+    # Patch p_align in the first Elf64_Phdr (LOAD) of the loader ELF.
+    # Elf64_Ehdr is 64 bytes; Elf64_Phdr.p_align is at offset 48 within
+    # the phdr → file offset 112. Written after cp, before strip.
+    substituteInPlace src/GNUmakefile --replace \
+      '$$(Q)cp $$< $$@' \
+      '$$(Q)cp $$< $$@ && printf '"'"'\x00\x00\x01\x00\x00\x00\x00\x00'"'"' | dd of=$$@ bs=1 seek=112 count=8 conv=notrunc 2>/dev/null'
+    # readelf is needed to generate loader-info.c (pokedata workaround offset).
+    # The Makefile calls bare 'readelf' but only the cross-prefixed version exists.
+    substituteInPlace src/GNUmakefile --replace "readelf -s" "${stdenv.cc.targetPrefix}readelf -s"
+    # AArch64 requires 16-byte-aligned SP. proot's transfer_load_script sets
+    # SP = stack_pointer − buffer_size, which may not be aligned. LLVM 21's
+    # loader uses SP-relative addressing in _start, so misalignment → SIGBUS.
+    # Fix: align SP down independently; keep x0 pointing to actual data.
+    patch -p1 < ${./align-sp.patch}
   '';
   buildInputs = [ talloc ];
   patches = [ ./detranslate-empty.patch ];

pkgs/proot-termux/sigbus-debug.patch

@@ -0,0 +1,20 @@
+--- a/src/tracee/event.c
++++ b/src/tracee/event.c
+@@ -668,6 +668,17 @@
+ 			break;
+ 		}
+
++		case SIGBUS: {
++			siginfo_t siginfo = {};
++			ptrace(PTRACE_GETSIGINFO, tracee->pid, NULL, &siginfo);
++			note(tracee, WARNING, INTERNAL,
++				"vpid %" PRIu64 ": SIGBUS si_code=%d si_addr=%p PC=0x%lx SP=0x%lx",
++				tracee->vpid, siginfo.si_code, siginfo.si_addr,
++				(unsigned long)peek_reg(tracee, CURRENT, INSTR_POINTER),
++				(unsigned long)peek_reg(tracee, CURRENT, STACK_POINTER));
++			break;
++		}
++
+ 		default:
+ 			/* Deliver this signal as-is,
+ 			 * unless we're chaining syscall.  */