Partial SEH support.

 * Removed linker script; .edata *and* .pdata required by MingW for SEH.
 * Removed buggy `-fdata-sections` and `-ffunction-sections`.

Signed-off-by: Toni Uhlig <[email protected]>

CRT/except.h

@@ -0,0 +1,35 @@
+#ifndef EXCEPT_H
+#define EXCEPT_H 1
+
+#ifndef __SEH__
+#error "SEH not supported by your toolchain!"
+#endif
+
+#ifdef __try1
+#undef __try1
+#endif
+
+#ifdef __except1
+#undef __except1
+#endif
+
+#define __dpptry(handler, counter)                                                                                     \
+    __asm__ goto(                                                                                                      \
+        ".seh_handler __C_specific_handler, @except\n\t"                                                               \
+        ".seh_handlerdata\n\t"                                                                                         \
+        ".long 1\n\t"                                                                                                  \
+        ".rva .l_startw" #counter ", .l_endw" #counter ", " #handler ", .l_exceptw" #counter                           \
+        "\n\t"                                                                                                         \
+        ".section .text\n"                                                                                             \
+        ".l_startw" #counter ":" :: ::except);
+
+#define __dppexcept(counter)                                                                                           \
+    goto end;                                                                                                          \
+    except:                                                                                                            \
+    __asm__(".l_exceptw" #counter ":");
+
+#define __dpptryend(counter)                                                                                           \
+    end:                                                                                                               \
+    __asm__(".l_endw" #counter ":");
+
+#endif

CRT/kcrt.c

@@ -6,6 +6,8 @@
 
 #include <ntddk.h>
 
+#include "except.h"
+
 #define KCRT_POOL_DEFAULT_TAG 0xDEADBEEF
 
 extern void (*__CTOR_LIST__)();

Makefile.deps

@@ -49,12 +49,12 @@ endif
 
 $(LIBCRT_BUILD_DIR)/kcrt$(NAME_SUFFIX).o: $(CC) $(DPP_ROOT)/CRT/kcrt.c
 	$(Q)test -d '$(LIBCRT_BUILD_DIR)' || mkdir -p '$(LIBCRT_BUILD_DIR)'
-	$(Q)$(CC) -std=c99 $(CFLAGS) -c CRT/kcrt.c -o $@
+	$(Q)$(CC) -std=gnu99 $(CFLAGS) -c CRT/kcrt.c -o $@
 	@echo 'CC  $@'
 
 $(LIBCRT_BUILD_DIR)/ntdll_zw_functions$(NAME_SUFFIX).o: $(CC) $(DPP_ROOT)/CRT/ntdll_zw_functions.c
 	$(Q)test -d '$(LIBCRT_BUILD_DIR)' || mkdir -p '$(LIBCRT_BUILD_DIR)'
-	$(Q)$(CC) -std=c99 $(CFLAGS) -c CRT/ntdll_zw_functions.c -o $@
+	$(Q)$(CC) -std=gnu99 $(CFLAGS) -c CRT/ntdll_zw_functions.c -o $@
 	@echo 'CC  $@'
 
 $(LIBCRT_BUILD_DIR)/eastl_compat$(NAME_SUFFIX).opp: $(CXX) $(DPP_ROOT)/CRT/eastl_compat.cpp

Makefile.inc

@@ -49,7 +49,7 @@ RC = $(LOCAL_MINGW64_RC)
 DDK_INCLUDE_DIR = $(dir $(CC))../x86_64-w64-mingw32/include/ddk
 CFLAGS := -Wall -Wextra -Wno-sign-compare -Wno-strict-aliasing \
 	-m64 -fPIC -fvisibility=hidden \
-	-ffunction-sections -fdata-sections -fno-builtin -ffreestanding \
+	-fno-builtin -ffreestanding \
 	-fno-stack-protector -mno-stack-arg-probe \
 	-I$(DPP_ROOT)/CRT -I$(DDK_INCLUDE_DIR) \
 	-D__INTRINSIC_DEFINED_InterlockedBitTestAndSet \
@@ -84,8 +84,7 @@ DRIVER_LDFLAGS := -shared \
 	-Wl,--exclude-all-symbols \
 	-Wl,--entry,_CRT_DriverEntry \
 	$(PRINT_LDSCRIPT) \
-	-nostartfiles -nodefaultlibs -nostdlib \
-	-T$(DPP_ROOT)/ld-script.txt
+	-nostartfiles -nodefaultlibs -nostdlib
 DRIVER_LIBS := -lntoskrnl -lhal
 USER_LDFLAGS := -Wl,--dynamicbase -Wl,--nxcompat -Wl,--gc-sections
 USER_LIBS :=
@@ -139,7 +138,7 @@ define BUILD_C_OBJECT
 	$(call CHECK_REQUIRED_PATHS)
 	$(call is_set,$(1),First argument: Source file missing)
 	$(call is_set,$(2),Second argument: Output object file missing)
-	$(Q)$(CC) -std=c99 $(CFLAGS) $(CUSTOM_CFLAGS) $(CFLAGS_$(2)) -c $(1) -o $(2)
+	$(Q)$(CC) -std=gnu99 $(CFLAGS) $(CUSTOM_CFLAGS) $(CFLAGS_$(2)) -c $(1) -o $(2)
 	@echo 'CC  $(2)'
 endef
 

Makefile.native.inc

@@ -21,7 +21,6 @@ CXX = /usr/bin/c++
 AR = /usr/bin/ar
 CFLAGS := -Wall -Wextra -Wno-sign-compare -Wno-strict-aliasing -Wno-c++20-compat \
 	-m64 -fPIC -fvisibility=hidden \
-	-ffunction-sections -fdata-sections \
 	-I$(DPP_ROOT)/CRT -DNATIVE=1
 ifneq ($(WERROR),)
 CFLAGS += -Werror
@@ -68,7 +67,7 @@ define BUILD_C_OBJECT
 	$(call CHECK_REQUIRED_PATHS)
 	$(call is_set,$(1),First argument: Source file missing)
 	$(call is_set,$(2),Second argument: Output object file missing)
-	$(Q)$(CC) -std=c99 $(CFLAGS) -c $(1) -o $(2)
+	$(Q)$(CC) -std=gnu99 $(CFLAGS) -c $(1) -o $(2)
 	@echo 'CC  $(2)'
 endef
 

README.md

@@ -18,7 +18,7 @@ Instead either use Zeranoe's build script with `make -C [path-to-this-repo] -f M
 
 1. `examples/dpp-template`: plain and stupid ddk C example
 2. `examples/dpp-template-cplusplus`: same, but written in C++, including a very complex class and some MT
-3. `examples/dpp-template-cplusplus-EASTL`: C++ example w/ (EA)STL integration, basicially everything usable except for SEH, VEH and assertions.
+3. `examples/dpp-template-cplusplus-EASTL`: C++ example w/ (EA)STL integration, basicially everything usable except for VEH and assertions.
 
 `examples/dpp-template-cplusplus-EASTL` supports `BUILD_NATIVE`!
 You can build and run it on your native Linux either with the other examples e.g. `make examples`, build only native executables `make -C examples DPP_ROOT="$(realpath .)" BUILD_NATIVE=1` in the top-level directory or directly build it from the examples directory with `make DPP_ROOT="$(realpath ..)" BUILD_NATIVE=1`.
@@ -195,6 +195,35 @@ You may reach a point where system functions, intrinsics or built-ins are requir
 For system functions that can be retrieved via `MmGetSystemRoutineAddress`, you may use `CRT/gen_wrapper.sh` to create wrapper modules. These modules retrieve the desired functions during run-time, but will be available during link-time. An example is `ZwTraceControl`, which gets exported by `ntdll.dll`.
 Eventually missing intrinsics/built-ins should be placed in `CRT/kcrt.c`.
 
+## Notes on SEH
+
+There are some limitations regarding the use of MingW's SEH implementation in kernel mode.
+You can not use it as you might have been known it from MSVC or MingW.
+
+Predefined statements `__try`, `__catch`, `__finally`, `__try1`, `__catch1`, etc. do **not** work!
+
+You need to use something like:
+
+```C
+#include <except.h>
+
+int handler(_In_ EXCEPTION_POINTERS * ep)
+{
+    (void)ep;
+    return EXCEPTION_EXECUTE_HANDLER;
+}
+
+// ...
+
+__dpptry(handler, unique_identifier) {
+    *(int *)0 = 0;
+} __dppexcept(unique_identifier) {
+    DbgPrint("%s\n", "Exception caught!");
+} __dpptryend(unique_identifier);
+```
+
+SEH needs to be improved. Patches are welcome!
+
 ## Known Issues
 
 Unfortunately, `eastl::to_string` does not work. See `CRT/eastl_compat.cpp` for more details.

examples/dpp-example.c

@@ -1,16 +1,58 @@
 #include <ntddk.h>
 
+#include <except.h>
+
 DRIVER_INITIALIZE DriverEntry;
 DRIVER_UNLOAD DriverUnload;
 
+extern NTSTATUS NTAPI ZwProtectVirtualMemory(_In_ HANDLE ProcessHandle,
+                                             _In_ _Out_ PVOID * BaseAddress,
+                                             _In_ _Out_ PULONG NumberOfBytesToProtect,
+                                             _In_ ULONG NewAccessProtection,
+                                             _Out_ PULONG OldAccessProtection);
+
+int example_exception_handler(_In_ EXCEPTION_POINTERS * lpEP)
+{
+    (void)lpEP;
+    DbgPrint("Exception handler called!\n");
+    return EXCEPTION_EXECUTE_HANDLER;
+}
+
+static void another_seh_test()
+{
+    DbgPrint("Another SEH test..\n");
+    __dpptry(example_exception_handler, anotherseh)
+    {
+        *(int *)0 = 0;
+    }
+    __dppexcept(anotherseh)
+    {
+        DbgPrint("Success!\n");
+    }
+    __dpptryend(anotherseh);
+}
+
 NTSTATUS DriverEntry(struct _DRIVER_OBJECT * DriverObject, PUNICODE_STRING RegistryPath)
 {
     (void)DriverObject;
     (void)RegistryPath;
 
     DbgPrint("%s\n", "Hello ring0!");
 
-    // This is bad. Please do not call _disable/_enable in the DriverEntry.
+    DbgPrint("Testing SEH..\n");
+    __dpptry(example_exception_handler, testseh)
+    {
+        *(int *)0 = 0;
+        DbgPrint("You should never see this text!\n");
+    }
+    __dppexcept(testseh)
+    {
+        DbgPrint("Success! SEH seems to work.\n");
+    }
+    __dpptryend(testseh);
+
+    another_seh_test();
+
     DbgPrint("%s\n", "Disable/Enable Interrupts!");
     _disable();
     _enable();