Working version

1 files changed, 106 insertions, 0 deletions

diff --git a/hacking.c b/hacking.c
new file mode 100644
index 0000000..3b42819
--- /dev/null
+++ b/hacking.c
@@ -0,0 +1,106 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <ffi.h>
+#include <elf.h>
+#include <libelf.h>
+
+#include "hacking.h"
+
+Callable* newCallable() {
+    Callable* c = malloc(sizeof(Callable));
+    c->cif = malloc(sizeof(ffi_cif));
+    c->fp = NULL;
+    return c;
+}
+
+Callable* funcnameToCallable(char* fname, 
+            uint8_t n_params, ffi_type** parameter_types, ffi_type* return_type) {
+    // http://stackoverflow.com/a/1118808/1544337
+    Elf64_Shdr * shdr;
+    Elf64_Ehdr * ehdr;
+    Elf *        elf;
+    Elf_Scn *    scn;
+    Elf_Data *   data;
+    int cnt;
+    void (*fp)() = NULL;
+    Callable* callable = newCallable();
+    if (callable == NULL) return NULL;
+
+    int fd = 0;
+
+    /* This is probably Linux specific - Read in our own executable*/
+    if ((fd = open("/proc/self/exe", O_RDONLY)) == -1)
+        exit(1);
+
+    elf_version(EV_CURRENT);
+
+    if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL) {
+        fprintf(stderr, "file is not an ELF binary\n");
+        exit(1);
+    }
+        /* Let's get the elf sections */
+    if (((ehdr = elf64_getehdr(elf)) == NULL) ||
+    ((scn = elf_getscn(elf, ehdr->e_shstrndx)) == NULL) ||
+    ((data = elf_getdata(scn, NULL)) == NULL)) {
+        fprintf(stderr, "Failed to get SOMETHING\n");
+        exit(1);
+    }
+
+    /* Let's go through each elf section looking for the symbol table */
+    for (cnt = 1, scn = NULL; (scn = elf_nextscn(elf, scn)); cnt++) {
+        if ((shdr = elf64_getshdr(scn)) == NULL)
+            exit(1);
+
+        if (shdr->sh_type == SHT_SYMTAB) {
+            char *name;
+            data = 0;
+            if ((data = elf_getdata(scn, data)) == 0 || data->d_size == 0) {
+                fprintf(stderr, "No data in symbol table\n");
+                continue;
+            }
+            
+            Elf64_Sym *esym = (Elf64_Sym*) data->d_buf;
+            Elf64_Sym *lastsym = (Elf64_Sym*) ((char*) data->d_buf + data->d_size);
+
+            /* Look through all symbols */ 
+            for (; esym < lastsym; esym++) {
+                if ((esym->st_value == 0) ||
+                        (ELF64_ST_BIND(esym->st_info)== STB_WEAK) ||
+                        (ELF64_ST_BIND(esym->st_info)== STB_NUM) ||
+                        (ELF64_ST_TYPE(esym->st_info)!= STT_FUNC)) 
+                    continue;
+
+                name = elf_strptr(elf,shdr->sh_link , (size_t)esym->st_name);
+
+                if(!name){
+                    fprintf(stderr,"%s\n",elf_errmsg(elf_errno()));
+                } else if(strcmp(fname, name) == 0 ) {
+                    fp = (void(*)(void)) esym->st_value;
+                }
+            }        
+
+            /* Call and hope we don't segfault!*/
+            if (fp != NULL) {
+                if (ffi_prep_cif(callable->cif, FFI_DEFAULT_ABI, n_params, return_type, parameter_types) == FFI_OK) {
+                    elf_end(elf);
+                    callable->fp = fp;
+                    return callable;
+                }
+            }
+        } 
+    }
+
+    elf_end(elf);
+
+    fprintf(stderr, "No function %s found\n", fname);
+
+    return NULL;
+}
+
+void call(Callable* callable, void** parameters, void* return_val) {
+    ffi_call(callable->cif, callable->fp, return_val, parameters);
+}
+