From 8cff58d5af8f65a881ea0da59322af57843f7dfe Mon Sep 17 00:00:00 2001
From: fincs <fincs@devkitpro.org>
Date: Sat, 31 Aug 2024 00:40:56 +0200
Subject: [PATCH] dynamic: add support for ELF packed relocations (relr)

---
 nx/source/runtime/dynamic.c | 38 +++++++++++++++++++++++++++++++++++++
 nx/switch.specs             |  2 +-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/nx/source/runtime/dynamic.c b/nx/source/runtime/dynamic.c
index c9e2587eb..d92e150e2 100644
--- a/nx/source/runtime/dynamic.c
+++ b/nx/source/runtime/dynamic.c
@@ -36,6 +36,10 @@ static void _dynProcessRela(uintptr_t base, const Elf64_Rela* rela, size_t relas
 				break;
 			}
 
+			case R_AARCH64_NONE: {
+				break;
+			}
+
 			case R_AARCH64_RELATIVE: {
 				u64* ptr = (u64*)(base + rela->r_offset);
 				*ptr = base + rela->r_addend;
@@ -45,6 +49,25 @@ static void _dynProcessRela(uintptr_t base, const Elf64_Rela* rela, size_t relas
 	}
 }
 
+static void _dynProcessRelr(uintptr_t base, const Elf64_Relr* relr, size_t relrsz)
+{
+	u64* ptr = NULL;
+	for (; relrsz--; relr++) {
+		if ((*relr & 1) == 0) {
+			ptr = (u64*)(base + *relr);
+			*ptr++ += base;
+		} else {
+			u64 bitmap = *relr >> 1;
+			while (bitmap) {
+				unsigned id = __builtin_ffsl(bitmap)-1;
+				bitmap &= ~(1UL << id);
+				ptr[id] += base;
+			}
+			ptr += 63;
+		}
+	}
+}
+
 void __nx_dynamic(uintptr_t base, const Mod0Header* mod0)
 {
 	// Return early if MOD0 header has been invalidated
@@ -65,6 +88,8 @@ void __nx_dynamic(uintptr_t base, const Mod0Header* mod0)
 	// Extract relevant information from the ELF dynamic section
 	const Elf64_Rela* rela = NULL;
 	size_t relasz = 0;
+	const Elf64_Relr* relr = NULL;
+	size_t relrsz = 0;
 	for (; dyn->d_tag != DT_NULL; dyn++) {
 		switch (dyn->d_tag) {
 			case DT_RELA:
@@ -74,6 +99,14 @@ void __nx_dynamic(uintptr_t base, const Mod0Header* mod0)
 			case DT_RELASZ:
 				relasz = dyn->d_un.d_val / sizeof(Elf64_Rela);
 				break;
+
+			case DT_RELR:
+				relr = (const Elf64_Relr*)(base + dyn->d_un.d_ptr);
+				break;
+
+			case DT_RELRSZ:
+				relrsz = dyn->d_un.d_val / sizeof(Elf64_Relr);
+				break;
 		}
 	}
 
@@ -82,6 +115,11 @@ void __nx_dynamic(uintptr_t base, const Mod0Header* mod0)
 		_dynProcessRela(base, rela, relasz);
 	}
 
+	// Apply RELR relocations if present
+	if (relr && relrsz) {
+		_dynProcessRelr(base, relr, relrsz);
+	}
+
 	// Return early if LNY0/LNY1 extensions are not present
 	if (mod0->magic_lny0 != 0x30594e4c || mod0->magic_lny1 != 0x31594e4c) { // LNY0, LNY1
 		return;
diff --git a/nx/switch.specs b/nx/switch.specs
index c486af8d8..a0f1eb1ef 100644
--- a/nx/switch.specs
+++ b/nx/switch.specs
@@ -1,5 +1,5 @@
 *link:
-+ -T %:getenv(DEVKITPRO /libnx/switch.ld) -pie --no-dynamic-linker --spare-dynamic-tags=0 --gc-sections -z text -z now -z nodynamic-undefined-weak --build-id=sha1 --nx-module-name
++ -T %:getenv(DEVKITPRO /libnx/switch.ld) -pie --no-dynamic-linker --spare-dynamic-tags=0 --gc-sections -z text -z now -z nodynamic-undefined-weak -z pack-relative-relocs --build-id=sha1 --nx-module-name
 
 *startfile:
 crti%O%s crtbegin%O%s --require-defined=main