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[Tinycc-devel] TCC modification simple boundschecking for windows


From: Simon Lehmayr
Subject: [Tinycc-devel] TCC modification simple boundschecking for windows
Date: Tue, 2 Dec 2008 11:58:33 +0100 (CET)

Hello,

I currently try to enable a mild boundschecking for the windows version. I 
already found out that malloc hooks are required to check allocated memory. But 
I don't use malloc in my programs. So I wanted a mild bounds-checking version 
working for me.
I also modified the make batch file to use tcc to compile itself. I use mingw 
ar.exe. tcc0 is the tcc compiled of previous run.
New batch file:
@rem ----------------------------------------------------
@rem batch file to build tcc using gcc and ar from mingw
@rem ----------------------------------------------------
:
@echo>..\config.h #define TCC_VERSION "0.9.24"
@echo>>..\config.h #define TCC_TARGET_PE 1
@echo>>..\config.h #define CONFIG_TCCDIR "."
:
tcc0 -fno-strict-aliasing ../tcc.c -o tcc.exe
tcc0 -fno-strict-aliasing ../tcc.c -D LIBTCC -c -o libtcc.o
tcc0 -fno-strict-aliasing ../bcheck.c -c
tcc0 tools/tiny_impdef.c -o tiny_impdef.exe
tcc0 tools/tiny_libmaker.c -o tiny_libmaker.exe
mkdir libtcc
ar rcs libtcc/libtcc.a libtcc.o
rem del libtcc.o
copy ..\libtcc.h libtcc
:
tcc0 -c lib/crt1.c
tcc0 -c lib/wincrt1.c
tcc0 -c lib/dllcrt1.c
tcc0 -c lib/dllmain.c
tcc0 -c lib/chkstk.S
tcc0 -c ../libtcc1.c
tcc0 -c ../alloca86.S
tcc0 -c ../alloca86-bt.S
ar rcs lib/libtcc1.a crt1.o wincrt1.o dllcrt1.o dllmain.o chkstk.o libtcc1.o 
alloca86.o alloca86-bt.o
@rem del *.o
del tcc0.exe
copy tcc.exe tcc0.exe
@pause

But I have the problem that I can't fix: My compiled test program won't run. It 
crashes with a memory access violation.

Test c program:
#include <stdio.h>
void main()
{
        volatile char a[9];
        a[8]=0; // should work fine
//      a[9]=0; // should cause exception
        printf("hello world\n");
}

I modified bcheck.c to include boundschecking in windows builds and added 
#undef CONFIG_TCC_MALLOC_HOOKS to remove the malloc hooks
I defined #define CONFIG_TCC_BCHECK in all .c files

I modified tccpe.c to add the required sections for bcheck. I think here is my 
error:
function pe_add_runtime_ex:
ST_FN void pe_add_runtime_ex(TCCState *s1, struct pe_info *pe)
{
    const char *start_symbol;
    unsigned long addr = 0;
    int pe_type = 0;

// ------------------------- new ----------------------------
#ifdef CONFIG_TCC_BCHECK
    if (do_bounds_check) {
        unsigned long *ptr;
        Section *init_section;
        unsigned char *pinit;
        int sym_index;

        /* XXX: add an object file to do that */
        ptr = section_ptr_add(bounds_section, sizeof(unsigned long));
        *ptr = 0;
        add_elf_sym(symtab_section, 0, 0,
                    ELF32_ST_INFO(STB_GLOBAL, STT_NOTYPE), 0,
                    bounds_section->sh_num, "__bounds_start");
        /* add bound check code */
//        snprintf(buf, sizeof(buf), "%s/%s", tcc_lib_path, "bcheck.o");
//        tcc_add_file(s1, buf);
#ifdef TCC_TARGET_I386
        if (s1->output_type != TCC_OUTPUT_MEMORY) {
            /* add 'call __bound_init()' in .init section */
            init_section = find_section(s1, ".init");
            pinit = section_ptr_add(init_section, 5);
            pinit[0] = 0xe8;
            put32(pinit + 1, -4);
            sym_index = find_elf_sym(symtab_section, "__bound_init");
            put_elf_reloc(symtab_section, init_section,
                          init_section->data_offset - 4, R_386_PC32, sym_index);
        }
#endif
    }
#endif
// ------------------------- end new ----------------------------

    if (find_elf_sym(symtab_section, "address@hidden"))
        pe_type = PE_GUI;
    else
    if (TCC_OUTPUT_DLL == s1->output_type) {
        pe_type = PE_DLL;
        /* need this for 'tccelf.c:relocate_section()' */
        s1->output_type = TCC_OUTPUT_EXE;
    }

    start_symbol =
        TCC_OUTPUT_MEMORY == s1->output_type
        ? PE_GUI == pe_type ? "_runwinmain" : NULL
        : PE_DLL == pe_type ? "address@hidden"
        : PE_GUI == pe_type ? "_winstart" : "_start"
        ;

    /* grab the startup code from libtcc1 */
    if (start_symbol)
        add_elf_sym(symtab_section,
            0, 0,
            ELF32_ST_INFO(STB_GLOBAL, STT_NOTYPE), 0,
            SHN_UNDEF, start_symbol);

    if (0 == s1->nostdlib) {
        tcc_add_library(s1, "tcc1");
#ifdef __CYGWIN__
        tcc_add_library(s1, "cygwin1");
#else
        tcc_add_library(s1, "msvcrt");
#endif
        tcc_add_library(s1, "kernel32");
        if (PE_DLL == pe_type || PE_GUI == pe_type) {
            tcc_add_library(s1, "user32");
            tcc_add_library(s1, "gdi32");
        }
    }

    if (start_symbol) {
        addr = (unsigned long)tcc_get_symbol_err(s1, start_symbol);
        if (s1->output_type == TCC_OUTPUT_MEMORY && addr)
            /* for -run GUI's, put '_runwinmain' instead of 'main' */
            add_elf_sym(symtab_section,
                    addr, 0,
                    ELF32_ST_INFO(STB_GLOBAL, STT_NOTYPE), 0,
                    text_section->sh_num, "main");
    }

    if (pe) {
        pe->type = pe_type;
        pe->start_addr = addr;
    }
}

I hope you can help me here. I think I'm just a little step away from the goal.
Simon


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