eh_elf: Implement step_cursor

src/eh_elf/context_struct.h

@@ -0,0 +1,13 @@
+#include <stdint.h>
+
+typedef struct {
+    uintptr_t rip, rsp, rbp;
+} unwind_context_t;
+
+typedef uintptr_t (*deref_func_t)(uintptr_t);
+
+typedef unwind_context_t (*_fde_func_t)(unwind_context_t, uintptr_t);
+typedef unwind_context_t (*_fde_func_with_deref_t)(
+        unwind_context_t,
+        uintptr_t,
+        deref_func_t);

src/eh_elf/eh_elf.c

@@ -13,6 +13,10 @@
  ************************************************/
 
 #include "eh_elf.h"
+#include "context_struct.h"
+#include "libunwind.h"
+#include "memory_map.h"
+#include "remote.h"
 
 int eh_elf_init_local() {
     return mmap_init_local();
@@ -26,7 +30,70 @@ void eh_elf_clear() {
     mmap_clear();
 }
 
-int eh_elf_step_cursor(struct cursor *cursor) {
-    // TODO implement
-    return 0;
+static struct {
+    unw_addr_space_t addr_space;
+    unw_accessors_t *accessors;
+    void* arg;
+} _fetch_state;
+
+static uintptr_t fetchw_here(uintptr_t addr) {
+    uintptr_t out;
+    fetchw(_fetch_state.addr_space,
+           _fetch_state.accessors,
+           &addr,
+           &out,
+           _fetch_state.arg);
+    return out;
+}
+
+int eh_elf_step_cursor(struct cursor *cursor) {
+    uintptr_t ip = cursor->dwarf.ip;
+
+    // Retrieve memory map entry
+    mmap_entry_t* mmap_entry = mmap_get_entry(ip);
+    if(mmap_entry == NULL)
+        return -1;
+
+    // Retrieve a pointer to the eh_elf function
+    _fde_func_with_deref_t fde_func =
+        (_fde_func_t) (dlsym(mmap_entry->eh_elf, "_eh_elf"));
+    if(fde_func == NULL)
+        return -2;
+
+    // Setup an eh_elf context
+    unwind_context_t eh_elf_context;
+    eh_elf_context.rip = ip;
+    eh_elf_context.rsp = cursor->dwarf.loc[UNW_TDEP_SP].val;
+    eh_elf_context.rbp = cursor->dwarf.loc[UNW_TDEP_BP].val;
+
+    // Set _fetch_state before passing fetchw_here
+    _fetch_state.addr_space = cursor->dwarf.as;
+    _fetch_state.accessors = &cursor->dwarf.as->acc;
+
+    // Call fde_func
+    eh_elf_context = fde_func(
+            eh_elf_context,
+            ip - mmap_entry->offset,
+            fetchw_here);
+
+    // Check for the end of the call chain
+    if(eh_elf_context.rbp == 0 || eh_elf_context.rip + 1 == 0)
+        return 0;
+
+    // Push back the data into libunwind's structures
+    for (int i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
+        cursor->dwarf.loc[i] = DWARF_NULL_LOC;
+
+    cursor->dwarf.loc[UNW_TDEP_BP].val = eh_elf_context.rbp;
+    cursor->dwarf.loc[UNW_TDEP_SP].val = eh_elf_context.rsp;
+    cursor->dwarf.loc[UNW_TDEP_IP].val = eh_elf_context.rip;
+    cursor->dwarf.use_prev_instr = 1;
+
+    cursor->frame_info.frame_type = UNW_X86_64_FRAME_GUESSED;
+    cursor->frame_info.cfa_reg_rsp = 0;
+    cursor->frame_info.cfa_reg_offset = 16;
+    cursor->frame_info.rbp_cfa_offset = -16;
+    cursor->dwarf.cfa += 16;
+
+    return 1;
 }

src/eh_elf/eh_elf.h

@@ -17,11 +17,6 @@
 #include <sys/types.h>
 #include "libunwind_i.h"
 
-/// Store the necessary data for a single eh_elf
-typedef struct {
-    // TODO
-} eh_elf_handle_t;
-
 /** Initialize everything for local memory analysis
  * @return 0 on success, or a negative value upon failure
  **/
@@ -37,6 +32,7 @@ void eh_elf_clear();
 
 /** Step the cursor using eh_elf mechanisms.
  *
- * Return 0 if everything went fine, otherwise, return a negative value.
+ * @return a positive value upon success, 0 if the frame before this unwinding
+ * was the last one, or a negative value upon failure.
  **/
 int eh_elf_step_cursor(struct cursor *cursor);