DynamicLoader: Remove math functionality in favor of -lgcc

This links the dynamic linker against libgcc.a instead of having
our own copy of the math functions.

For now we need to specify -fbuilding-libgcc as a hack to work
around a bug with the -nodefaultlibs flag. Once everyone is on
the latest toolchain version this can be removed.

Userland/DynamicLoader/CMakeLists.txt

@@ -1,6 +1,5 @@
 set(LOADER_SOURCES
     main.cpp
-    math.cpp
     misc.cpp
 )
 
@@ -23,11 +22,13 @@ add_definitions(-D_DYNAMIC_LOADER)
 
 set(SOURCES ${LOADER_SOURCES} ${AK_SOURCES} ${ELF_SOURCES} ${LIBC_SOURCES1} ${LIBC_SOURCES2} ${LIBC_SOURCES3} ${LIBSYSTEM_SOURCES})
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti -nostdlib -pie -fpic -DNO_TLS")
+# FIXME: Remove -fbuilding-libgcc after the next toolchain update
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fbuilding-libgcc -fno-rtti -nostdlib -pie -fpic -DNO_TLS")
 
 set_source_files_properties (../Libraries/LibC/ssp.cpp PROPERTIES COMPILE_FLAGS
     "-fno-stack-protector")
 
 add_executable(Loader.so ${SOURCES})
+target_link_libraries(Loader.so gcc)
 target_link_options(Loader.so PRIVATE LINKER:--no-dynamic-linker)
 install(TARGETS Loader.so RUNTIME DESTINATION usr/lib/)

Userland/DynamicLoader/main.cpp

@@ -116,4 +116,10 @@ void _start(int argc, char** argv, char** envp)
     ELF::DynamicLinker::linker_main(move(main_program_name), main_program_fd, is_secure, argc, argv, envp);
     VERIFY_NOT_REACHED();
 }
+
+void _fini();
+
+void _fini()
+{
+}
 }

Userland/DynamicLoader/math.cpp

@@ -1,170 +0,0 @@
-/*
- * Copyright (c) 2020, the SerenityOS developers.
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-// TODO: Is there a compiler flag we can use to still get these math functions? (and compile with -nostdlib)
-// FIXME: What do we do with this regarding copyright stuff?
-// code for math functions taken from here:
-// https://gitlab.incom.co/CM-Shield/u-boot/commit/aa7839b39c2ee77f9ab8c393c56b8d812507dbb7
-// https://github.com/zayac/qemu-arm/blob/master/qemu/roms/ipxe/src/libgcc/__udivmoddi4.c
-// https://code.woboq.org/llvm/compiler-rt/lib/builtins/divdi3.c.html
-
-#include "math.h"
-
-extern "C" {
-
-union overlay64 {
-    u64 longw;
-    struct {
-        u32 lower;
-        u32 higher;
-    } words;
-};
-
-u64 __ashldi3(u64 num, unsigned int shift)
-{
-    union overlay64 output;
-
-    output.longw = num;
-    if (shift >= 32) {
-        output.words.higher = output.words.lower << (shift - 32);
-        output.words.lower = 0;
-    } else {
-        if (!shift)
-            return num;
-        output.words.higher = (output.words.higher << shift) | (output.words.lower >> (32 - shift));
-        output.words.lower = output.words.lower << shift;
-    }
-    return output.longw;
-}
-
-u64 __lshrdi3(u64 num, unsigned int shift)
-{
-    union overlay64 output;
-
-    output.longw = num;
-    if (shift >= 32) {
-        output.words.lower = output.words.higher >> (shift - 32);
-        output.words.higher = 0;
-    } else {
-        if (!shift)
-            return num;
-        output.words.lower = output.words.lower >> shift | (output.words.higher << (32 - shift));
-        output.words.higher = output.words.higher >> shift;
-    }
-    return output.longw;
-}
-
-#define MAX_32BIT_UINT ((((u64)1) << 32) - 1)
-
-static u64 _64bit_divide(u64 dividend, u64 divider, u64* rem_p)
-{
-    u64 result = 0;
-
-    /*
-	 * If divider is zero - let the rest of the system care about the
-	 * exception.
-	 */
-    if (!divider)
-        return 1 / (u32)divider;
-
-    /* As an optimization, let's not use 64 bit division unless we must. */
-    if (dividend <= MAX_32BIT_UINT) {
-        if (divider > MAX_32BIT_UINT) {
-            result = 0;
-            if (rem_p)
-                *rem_p = divider;
-        } else {
-            result = (u32)dividend / (u32)divider;
-            if (rem_p)
-                *rem_p = (u32)dividend % (u32)divider;
-        }
-        return result;
-    }
-
-    while (divider <= dividend) {
-        u64 locald = divider;
-        u64 limit = __lshrdi3(dividend, 1);
-        int shifts = 0;
-
-        while (locald <= limit) {
-            shifts++;
-            locald = locald + locald;
-        }
-        result |= __ashldi3(1, shifts);
-        dividend -= locald;
-    }
-
-    if (rem_p)
-        *rem_p = dividend;
-
-    return result;
-}
-
-u64 __udivdi3(u64 num, u64 den)
-{
-    return _64bit_divide(num, den, nullptr);
-}
-
-u64 __umoddi3(u64 num, u64 den)
-{
-    u64 v = 0;
-
-    _64bit_divide(num, den, &v);
-    return v;
-}
-
-uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t* rem_p)
-{
-    uint64_t quot = 0, qbit = 1;
-
-    if (den == 0) {
-        return 1 / ((unsigned)den); /* Intentional divide by zero, without
-				 triggering a compiler warning which
-				 would abort the build */
-    }
-
-    /* Left-justify denominator and count shift */
-    while ((int64_t)den >= 0) {
-        den <<= 1;
-        qbit <<= 1;
-    }
-
-    while (qbit) {
-        if (den <= num) {
-            num -= den;
-            quot += qbit;
-        }
-        den >>= 1;
-        qbit >>= 1;
-    }
-
-    if (rem_p)
-        *rem_p = num;
-
-    return quot;
-}
-int64_t __divdi3(int64_t a, int64_t b)
-{
-    const int bits_in_dword_m1 = (int)(sizeof(int64_t) * 8) - 1;
-    int64_t s_a = a >> bits_in_dword_m1;                   // s_a = a < 0 ? -1 : 0
-    int64_t s_b = b >> bits_in_dword_m1;                   // s_b = b < 0 ? -1 : 0
-    a = (a ^ s_a) - s_a;                                   // negate if s_a == -1
-    b = (b ^ s_b) - s_b;                                   // negate if s_b == -1
-    s_a ^= s_b;                                            // sign of quotient
-    return (__udivmoddi4(a, b, (uint64_t*)0) ^ s_a) - s_a; // negate if s_a == -1
-}
-int64_t __moddi3(int64_t a, int64_t b)
-{
-    const int bits_in_dword_m1 = (int)(sizeof(int64_t) * 8) - 1;
-    int64_t s = b >> bits_in_dword_m1; // s = b < 0 ? -1 : 0
-    b = (b ^ s) - s;                   // negate if s == -1
-    s = a >> bits_in_dword_m1;         // s = a < 0 ? -1 : 0
-    a = (a ^ s) - s;                   // negate if s == -1
-    uint64_t r = 0;
-    __udivmoddi4(a, b, &r);
-    return ((int64_t)r ^ s) - s; // negate if s == -1
-}
-}

Userland/DynamicLoader/math.h

@@ -1,26 +0,0 @@
-/*
- * Copyright (c) 2020, the SerenityOS developers.
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#pragma once
-
-#include <AK/Types.h>
-
-extern "C" {
-
-u64 __ashldi3(u64 num, unsigned int shift);
-
-u64 __lshrdi3(u64 num, unsigned int shift);
-
-u64 __udivdi3(u64 num, u64 den);
-
-u64 __umoddi3(u64 num, u64 den);
-
-uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t* rem_p);
-
-int64_t __divdi3(int64_t a, int64_t b);
-
-int64_t __moddi3(int64_t a, int64_t b);
-}