Write proper plt relocations in entry assembly, fix stack checking not working correctly

build.sh

@@ -3,17 +3,12 @@
 [ ! -d "lib" ] && mkdir "lib"
 [ ! -d "bin" ] && mkdir "bin"
 
+[ "$1" != "-shared" ] && echo "static"
+
 nasm -f elf64 "src/linux/crt_entry.asm" -o "bin/crt_entry.o"
 clang -fPIC -nostdlib -I "include" -g "src/linux/crt_ctors.c" -c -o "bin/crt_ctors.o"
 clang -fPIC -nostdlib -I "include" -g "src/ciabatta.c" -c -o "bin/ciabatta.o"
 
-rm "$LIB_FILE" 2> /dev/null
-
-if [ "$1" != "-shared" ]; then
-    [ -f "lib/ciabatta.a" ] && rm "lib/ciabatta.a"
-    llvm-ar -q "lib/ciabatta.a" "bin/crt_ctors.o" "bin/crt_entry.o" "bin/ciabatta.o"
-else
-    clang -fPIC -nostdlib -shared -o "lib/ciabatta.so" "bin/ciabatta.o"
-    cp "bin/crt_ctors.o" "lib/ctors.o"
-    cp "bin/crt_entry.o" "lib/entry.o"
-fi
+# Create a test executable
+clang -pie -nostdlib -Iinclude \
+    tests/empty.c bin/ciabatta.o bin/crt_ctors.o bin/crt_entry.o

src/linux/crt_entry.asm

@@ -2,20 +2,12 @@
 bits 64
 
 section .text
-
-global _start
-; global _init
-; global _fini
-extern __libc_global_fini
-extern __libc_global_init
-extern __libc_start_main
-extern main
-
-; _init:
-;     push ebp
-;     mov ebp, esp
-; _fini:
-
+    default rel
+    global _start
+    extern __libc_global_fini
+    extern __libc_global_init
+    extern __libc_start_main
+    extern main
 _start:
     xor ebp, ebp
     ;; Save rtld_fini address to r9
@@ -28,20 +20,16 @@ _start:
     push rax
     push rsp
     ;; Load fini and init initializers as function parameters
-    %ifdef CIA_SHARED
-        mov rcx, __libc_global_init wrt ..got
-        mov r8, __libc_global_fini wrt ..got
-    %else
-        mov rcx, __libc_global_init
-        mov r8, __libc_global_fini
-    %endif
-    mov rdi, main
+    push rbx
+    lea rbx, [__libc_global_init wrt ..plt]
+    mov rcx, rbx
+    lea rbx, [__libc_global_fini wrt ..plt]
+    mov r8, rbx
+    lea rbx, [main wrt ..plt]
+    mov rdi, rbx
+    pop rbx
     ;; Call start main
-    %ifdef CIA_SHARED
     call __libc_start_main wrt ..plt
-    %else
-        call __libc_start_main
-    %endif
     ;; No idea why halt it, I guess that's a funny
     ;; way to crash your application if the function we called
     ;; returns instead of calling the exit syscall

src/linux/entry.c

@@ -10,15 +10,15 @@ void __libc_start_main(
     int argc, char **argv,
     int (*init)(int, char**, char**),
     void (*fini)(void),
-    void (*runtime_ld_fini)(void),
+    void (*dl_fini)(void),
     void *stack_end
 ) {
+    // Get the envp
     char **envp = argv + (argc + 1);
     init(argc, argv, envp);
     main(argc, argv, envp);
     fini();
-    if(runtime_ld_fini != NULL) {
-        runtime_ld_fini();
-    }
+    // glibc bug
+    dl_fini();
     syscall_exit(0);
 }

src/linux/syscall.c

@@ -1,10 +1,35 @@
 
 #if os_is_linux()
 
+// Standard handles file descriptors
 #define STDIN_FILENO  0
 #define STDOUT_FILENO 1
 #define STDERR_FILENO 2
 
+// arch_prctl syscall codes
+#define ARCH_SET_GS    0x1001
+#define ARCH_SET_FS    0x1002
+#define ARCH_GET_FS    0x1003
+#define ARCH_GET_GS    0x1004
+#define ARCH_GET_CPUID 0x1011
+#define ARCH_SET_CPUID 0x1012
+
+// open syscall modes
+#define O_ACCMODE   0003
+#define O_RDONLY    00
+#define O_WRONLY    01
+#define O_RDWR      02
+#define O_CREAT     0100     /* not fcntl */
+#define O_EXCL      0200     /* not fcntl */
+#define O_NOCTTY    0400     /* not fcntl */
+#define O_TRUNC     01000    /* not fcntl */
+#define O_APPEND    02000
+#define O_NONBLOCK  04000
+#define O_NDELAY    O_NONBLOCK
+#define O_SYNC      010000
+#define O_FSYNC     O_SYNC
+#define O_ASYNC     020000
+
 #define SYS_read           0
 #define SYS_write          1
 #define SYS_open           2
@@ -67,6 +92,8 @@
 #define SYS_execve         59
 #define SYS_exit           60
 
+#define SYS_arch_prctl     158
+
 // Syscall stubs
 
 static __inline i64 __syscall0(i64 n) {
@@ -132,10 +159,26 @@ static inline i64 syscall_write(u32 fd, char const *buf, u64 count) {
     return __syscall3(SYS_write, (i64)fd, (i64)buf, (u64)count);
 }
 
+static inline i64 syscall_open(char const *filename, int flags, int mode) {
+    return __syscall3(SYS_open, (i64)filename, (i64)flags, (i64)mode);
+}
+
+static inline i64 syscall_close(u32 fd) {
+    return __syscall1(SYS_close, fd);
+}
+
 static inline i64 syscall_exit(int code) {
     return __syscall1(SYS_exit, (i64)code);
 }
 
+static inline i64 syscall_arch_prctl_set(int code, u64 value) {
+    return __syscall2(SYS_arch_prctl, code, (i64)value);
+}
+
+static inline i64 syscall_arch_prctl_get(int code, u64 *value) {
+    return __syscall2(SYS_arch_prctl, code, (i64)value);
+}
+
 #else
 #error "syscall.h should only be included in LINUX code"
 #endif

test.c

@@ -0,0 +1,8 @@
+
+#include <stdio.h>
+
+int main() {
+    char string[] = "hi";
+    printf("%s\n", string);
+    return 0;
+}

test.sh

@@ -1,8 +0,0 @@
-#!/bin/bash
-
-if [ "$1" != "-shared" ]; then
-    clang -static -nostdlib tests/empty.c lib/ciabatta.a -Iinclude
-else
-    clang -g -fno-stack-protector -fPIE tests/empty.c -c -o tests/empty.o
-    ld -no-pie -nostdlib lib/entry.o tests/empty.o lib/ciabatta.so lib/ctors.o -Iinclude
-fi

tests/empty.c

@@ -15,8 +15,8 @@ static inline i64 syscall_write(u32 fd, char const *buf, u64 count) {
     return __syscall3(SYS_write, (i64)fd, (i64)buf, (u64)count);
 }
 
-char string[] = "Hello, world!\n";
 int main(int argc, char **argv, char **envp) {
+    char string[] = "Hello, world!\n";
     syscall_write(STDOUT_FILENO, string, sizeof string);
     return 0;
 }