Relocating COM32 module

2 files changed, 150 insertions, 0 deletions

diff --git a/com32/gdbstub/Makefile b/com32/gdbstub/Makefile
new file mode 100644
index 00000000..d9e55c8c
--- /dev/null
+++ b/com32/gdbstub/Makefile
@@ -0,0 +1,48 @@
+## -----------------------------------------------------------------------
+##
+##   Copyright 2001-2008 H. Peter Anvin - All Rights Reserved
+##
+##   This program is free software; you can redistribute it and/or modify
+##   it under the terms of the GNU General Public License as published by
+##   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+##   Boston MA 02110-1301, USA; either version 2 of the License, or
+##   (at your option) any later version; incorporated herein by reference.
+##
+## -----------------------------------------------------------------------
+
+##
+## GDB remote debugging
+##
+
+topdir = ../..
+include ../MCONFIG
+
+CFLAGS += -fPIE
+
+LIBS	   = ../libutil/libutil_com.a ../lib/libcom32.a $(LIBGCC)
+LNXLIBS	   = ../libutil/libutil_lnx.a
+
+MODULES	  = gdbstub.c32
+TESTFILES =
+
+OBJS = main.o
+
+all: $(MODULES) $(TESTFILES)
+
+gdbstub.elf : $(OBJS) $(LIBS) $(C_LIBS)
+	$(LD) $(LDFLAGS) -o $@ $^
+
+tidy dist:
+	rm -f *.o *.lo *.a *.lst *.elf .*.d *.tmp
+
+clean: tidy
+	rm -f *.lss *.c32 *.lnx *.com
+
+spotless: clean
+	rm -f *~ \#*
+
+install: all
+	mkdir -m 755 -p $(INSTALLROOT)$(AUXDIR)
+	install -m 644 $(MODULES) $(INSTALLROOT)$(AUXDIR)
+
+-include .*.d
diff --git a/com32/gdbstub/main.c b/com32/gdbstub/main.c
new file mode 100644
index 00000000..11c4e08b
--- /dev/null
+++ b/com32/gdbstub/main.c
@@ -0,0 +1,102 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <console.h>
+#include <com32.h>
+#include <syslinux/loadfile.h>
+
+#define COM32_LOAD_ADDR ((void*)0x101000)
+#define STACK_RED_ZONE  0x1000
+
+static inline void error(const char *msg)
+{
+    fputs(msg, stderr);
+}
+
+static void shift_cmdline(struct com32_sys_args *com32)
+{
+    char *p;
+
+    /* Skip leading whitespace */
+    for (p = com32->cs_cmdline; *p != '\0' && *p == ' '; p++)
+        ;
+
+    /* Skip first word */
+    for (; *p != '\0' && *p != ' '; p++)
+        ;
+
+    /* Skip whitespace after first word */
+    for (; *p != '\0' && *p == ' '; p++)
+        ;
+
+    com32->cs_cmdline = p;
+}
+
+static __noreturn reloc_entry(void *ptr, size_t len, uintptr_t entry_esp, uintptr_t module_esp)
+{
+    size_t stack_frame_size = sizeof(struct com32_sys_args) + 4;
+    struct com32_sys_args *com32;
+
+    /* Copy module to load address */
+    memcpy(COM32_LOAD_ADDR, ptr, len);
+
+    /* Copy stack frame onto module stack */
+    module_esp = (module_esp - stack_frame_size) & ~15;
+    memcpy((void*)module_esp, (void*)entry_esp, stack_frame_size);
+
+    /* Fix up command line */
+    com32 = (struct com32_sys_args*)((char*)module_esp + 4);
+    shift_cmdline(com32);
+
+    /* Invoke module with stack set up */
+    asm volatile (
+            "movl %0, %%esp\n\t"
+            "jmp *%%ecx"
+            : : "r"(module_esp), "c"(COM32_LOAD_ADDR)
+    );
+    for(;;); /* shut the compiler up */
+}
+
+static inline __noreturn reloc(void *ptr, size_t len)
+{
+    extern uintptr_t __entry_esp;
+    extern char _start[], _end[];
+    size_t total_size = _end - _start;
+    __noreturn (*success_fn)(void*, size_t, uintptr_t, uintptr_t);
+    uint32_t esp;
+    char *dest;
+
+    /* Calculate relocation address, preserve current stack */
+    asm volatile ("movl %%esp, %0\n\t" : "=m"(esp));
+    dest = (char*)((esp - STACK_RED_ZONE - total_size) & ~3);
+
+    /* Calculate entry point in relocated code */
+    success_fn = (void*)(dest + ((char*)reloc_entry - _start));
+
+    /* Copy all sections to relocation address */
+    printf("Relocating %d bytes from %p to %p\n", total_size, _start, dest);
+    memcpy(dest, _start, total_size);
+
+    success_fn(ptr, len, __entry_esp, (uintptr_t)dest);
+}
+
+int main(int argc, char *argv[])
+{
+    void *data;
+    size_t data_len;
+
+    openconsole(&dev_null_r, &dev_stdcon_w);
+
+    if (argc < 2) {
+        error("Usage: gdbstub.c32 com32_file arguments...\n");
+        return 1;
+    }
+
+    if (loadfile(argv[1], &data, &data_len)) {
+        error("Unable to load file\n");
+        return 1;
+    }
+
+    /* No more lib calls after this point */
+    reloc(data, data_len);
+}