Implement RISC-V dynamic linking

.github/workflows/main.yml

@@ -9,14 +9,7 @@ jobs:
       matrix:
         compiler: [gcc, clang]
         architecture: [arm, riscv]
-        link_mode: [static]
-        include:
-          - compiler: gcc
-            architecture: arm
-            link_mode: dynamic
-          - compiler: clang
-            architecture: arm
-            link_mode: dynamic
+        link_mode: [static, dynamic]
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -27,6 +20,9 @@ jobs:
           sudo apt-get install -q -y qemu-user
           sudo apt-get install -q -y build-essential
           sudo apt-get install -q -y gcc-arm-linux-gnueabihf
+          sudo wget -q https://github.com/riscv-collab/riscv-gnu-toolchain/releases/download/2026.04.05/riscv32-glibc-ubuntu-24.04-gcc.tar.xz
+          sudo tar Jxf riscv32-glibc-ubuntu-24.04-gcc.tar.xz -C /opt
+          echo "/opt/riscv/bin" >> "$GITHUB_PATH"
       - name: Determine static or dynamic linking mode
         id: determine-mode
         run: |

Makefile

@@ -49,10 +49,6 @@ STAGE0_FLAGS ?= --dump-ir
 STAGE1_FLAGS ?=
 DYNLINK ?= 0
 ifeq ($(DYNLINK),1)
-    ifeq ($(ARCH),riscv)
-        # TODO: implement dynamic linking for RISC-V.
-        $(error "Dynamic linking mode is not implemented for RISC-V")
-    endif
     STAGE0_FLAGS += --dynlink
     STAGE1_FLAGS += --dynlink
 endif
@@ -108,8 +104,10 @@ check-sanitizer: $(OUT)/$(STAGE0)-sanitizer tests/driver.sh
 	$(Q)rm $(OUT)/shecc
 
 check-snapshots: $(OUT)/$(STAGE0) $(SNAPSHOTS) tests/check-snapshots.sh
+	# static linking
 	$(Q)$(foreach SNAPSHOT_ARCH, $(ARCHS), $(MAKE) distclean config check-snapshot ARCH=$(SNAPSHOT_ARCH) DYNLINK=0 --silent;)
-	$(Q)$(MAKE) distclean config check-snapshot ARCH=arm DYNLINK=1 --silent
+	# dynamic linking
+	$(Q)$(foreach SNAPSHOT_ARCH, $(ARCHS), $(MAKE) distclean config check-snapshot ARCH=$(SNAPSHOT_ARCH) DYNLINK=1 --silent;)
 	$(VECHO) "Switching backend back to %s (DYNLINK=0)\n" arm
 	$(Q)$(MAKE) distclean config ARCH=arm DYNLINK=0 --silent
 
@@ -134,8 +132,10 @@ check-abi-stage2: $(OUT)/$(STAGE2)
 	fi
 
 update-snapshots: tests/update-snapshots.sh
+	# static linking
 	$(Q)$(foreach SNAPSHOT_ARCH, $(ARCHS), $(MAKE) distclean config update-snapshot ARCH=$(SNAPSHOT_ARCH) DYNLINK=0 --silent;)
-	$(Q)$(MAKE) distclean config update-snapshot ARCH=arm DYNLINK=1 --silent
+	# dynamic linking
+	$(Q)$(foreach SNAPSHOT_ARCH, $(ARCHS), $(MAKE) distclean config update-snapshot ARCH=$(SNAPSHOT_ARCH) DYNLINK=1 --silent;)
 	$(VECHO) "Switching backend back to %s (DYNLINK=0)\n" arm
 	$(Q)$(MAKE) distclean config ARCH=arm DYNLINK=0 --silent
 

mk/arm.mk

@@ -16,6 +16,7 @@ ARCH_DEFS = \
     \#define LIBC_SO \"libc.so.6\"\n$\
     \#define PLT_FIXUP_SIZE 20\n$\
     \#define PLT_ENT_SIZE 12\n$\
+    \#define RESERVED_GOT_NUM 3\n$\
     \#define R_ARCH_JUMP_SLOT 0x16\n$\
     \#define MAX_ARGS_IN_REG 4\n$\
     "

mk/riscv.mk

@@ -7,13 +7,40 @@ ARCH_DEFS = \
     \#define ARCH_PREDEFINED \"__riscv\" /* Older versions of the GCC toolchain defined __riscv__ */\n$\
     \#define ELF_MACHINE 0xf3\n$\
     \#define ELF_FLAGS 0\n$\
-    \#define DYN_LINKER \"/lib/ld-linux.so.3\"\n$\
+    \#define DYN_LINKER \"/lib/ld-linux-riscv32-ilp32d.so.1\"\n$\
     \#define LIBC_SO \"libc.so.6\"\n$\
-    \#define PLT_FIXUP_SIZE 20\n$\
-    \#define PLT_ENT_SIZE 12\n$\
+    \#define PLT_FIXUP_SIZE 32\n$\
+    \#define PLT_ENT_SIZE 16\n$\
+    \#define RESERVED_GOT_NUM 2\n$\
     \#define R_ARCH_JUMP_SLOT 0x5\n$\
     \#define MAX_ARGS_IN_REG 8\n$\
     "
 
-# TODO: Set this variable for RISC-V architecture
-RUNNER_LD_PREFIX=
+ifeq ($(USE_QEMU),1)
+    ifeq ($(DYNLINK),1)
+        CROSS_COMPILE = riscv32-unknown-linux-gnu-
+        RISCV_CC = $(CROSS_COMPILE)gcc
+        RISCV_CC := $(shell which $(RISCV_CC))
+        ifndef RISCV_CC
+            $(error "Unable to find ARM GNU toolchain.")
+        endif
+
+        LD_LINUX_PATH := $(shell cd $(shell $(RISCV_CC) --print-sysroot) 2>/dev/null && pwd)
+        ifeq ("$(LD_LINUX_PATH)","/")
+            LD_LINUX_PATH := $(shell dirname "$(shell which $(RISCV_CC))")/..
+            LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+            LD_LINUX_PATH := $(LD_LINUX_PATH)/$(shell echo $(CROSS_COMPILE) | sed s'/.$$//')/libc
+            LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+            ifndef LD_LINUX_PATH
+                LD_LINUX_PATH = /usr/$(shell echo $(CROSS_COMPILE) | sed s'/.$$//')
+                LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+            endif
+        endif
+
+        ifndef LD_LINUX_PATH
+            $(error "Dynamic linking mode requires ld-linux.so")
+        endif
+
+        RUNNER_LD_PREFIX = -L $(LD_LINUX_PATH)
+    endif
+endif

src/arch-lower.c

@@ -59,9 +59,9 @@ void riscv_lower(void)
 /* Entry point: dispatch to the active architecture. */
 void arch_lower(void)
 {
-#if ELF_MACHINE == 0x28 /* ARM */
+#if ELF_MACHINE == ELF_MACHINE_ARM32
     arm_lower();
-#elif ELF_MACHINE == 0xf3 /* RISC-V */
+#elif ELF_MACHINE == ELF_MACHINE_RV32
     riscv_lower();
 #else
     /* Unknown architecture: keep behavior as-is. */

src/defs.h

@@ -43,6 +43,7 @@
 #define MAX_DYNSYM 1024
 #define MAX_DYNSTR 1024
 #define MAX_RELPLT 1024
+#define MAX_RELAPLT 1024
 #define MAX_PLT 1024
 #define MAX_GOTPLT 1024
 #define MAX_CONSTANTS 1024
@@ -101,6 +102,9 @@
 #define ALIGN_UP(val, align) (((val) + (align) - 1) & ~((align) - 1))
 #endif
 
+#define ELF_MACHINE_ARM32 0x28
+#define ELF_MACHINE_RV32 0xf3
+
 /* Common data structures */
 typedef struct arena_block {
     char *memory;
@@ -682,15 +686,28 @@ typedef struct {
     strbuf_t *elf_dynsym;
     strbuf_t *elf_dynstr;
     strbuf_t *elf_relplt;
+    strbuf_t *elf_relaplt;
     strbuf_t *elf_plt;
     strbuf_t *elf_got;
     int elf_interp_start;
     int elf_relplt_start;
+    int elf_relaplt_start;
     int elf_plt_start;
     int elf_got_start;
     int relplt_size;
+    int relaplt_size;
     int plt_size;
     int got_size;
+
+    /* Currently, we don't consider the scenarios involving
+     * a mixture of REL and RELA relocation entries.
+     *
+     * Therefore, use a flag to determine the type of
+     * relocation entries to be processed:
+     * - true: use RELA relocation entries
+     * - false: use REL relocation entries
+     */
+    bool use_relaplt;
 } dynamic_sections_t;
 
 /* For .dynsym section. */
@@ -709,6 +726,12 @@ typedef struct {
     int r_info;
 } elf32_rel_t;
 
+typedef struct {
+    int r_offset;
+    int r_info;
+    int r_addend;
+} elf32_rela_t;
+
 /* For .dynamic section */
 typedef struct {
     int d_tag;