From 5635365d394cbd29812a06bd5f7d1b0b53de5d0f Mon Sep 17 00:00:00 2001
From: QinlinChen <chenqinlin98@gmail.com>
Date: Mon, 5 Jul 2021 21:55:07 +0800
Subject: [PATCH] afl-clang-fast: modify edit_params() to handle '-r'
 parameters for partial linking

There is a case that AFL cannot compile busybox. It is because the
building system of busybox uses the partial linking feature of ld
while the afl-clang-fast cannot handle such case.

More specifically, the building system of busybox first merges several
relocatable object file into a new relocatable file using the '-r'
option, where the afl-llvm-rt.o added by afl-clang-fast is also merged,
so the new relocatable file contains the symbols from afl-llvm-rt.o.
At the final linking step, the new relocatable file is linked with
afl-llvm-rt.o (added again by afl-clang-fast) into the executable file,
but both files contain the definitions of the symbols from afl-llvm-rt.o.
As a result, the compiler complains that and stop the building process.

I fix this by restraining afl-clang-fast from adding the 'afl-llvm-rt.o'
parameter when seeing the '-r', '-Wl,-r', or '-Wl,-i' in the cmd line.
---
 llvm_mode/afl-clang-fast.c | 36 +++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/llvm_mode/afl-clang-fast.c b/llvm_mode/afl-clang-fast.c
index 2104a1244..fdfc54f4d 100644
--- a/llvm_mode/afl-clang-fast.c
+++ b/llvm_mode/afl-clang-fast.c
@@ -103,7 +103,7 @@ static void find_obj(u8* argv0) {
 
 static void edit_params(u32 argc, char** argv) {
 
-  u8 fortify_set = 0, asan_set = 0, x_set = 0, bit_mode = 0;
+  u8 fortify_set = 0, asan_set = 0, x_set = 0, bit_mode = 0, partial_linking = 0;
   u8 *name;
 
   cc_params = ck_alloc((argc + 128) * sizeof(u8*));
@@ -148,6 +148,10 @@ static void edit_params(u32 argc, char** argv) {
     if (!strcmp(cur, "armv7a-linux-androideabi")) bit_mode = 32;
     if (!strcmp(cur, "-m64")) bit_mode = 64;
 
+    if (!strcmp(cur, "-Wl,-r") ||
+        !strcmp(cur, "-Wl,-i") ||
+        !strcmp(cur, "-r")) partial_linking = 1;
+
     if (!strcmp(cur, "-x")) x_set = 1;
 
     if (!strcmp(cur, "-fsanitize=address") ||
@@ -278,28 +282,30 @@ static void edit_params(u32 argc, char** argv) {
   }
 
 #ifndef __ANDROID__
-  switch (bit_mode) {
+  if (!partial_linking) {
+    switch (bit_mode) {
 
-    case 0:
-      cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt.o", obj_path);
-      break;
+      case 0:
+        cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt.o", obj_path);
+        break;
 
-    case 32:
-      cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt-32.o", obj_path);
+      case 32:
+        cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt-32.o", obj_path);
 
-      if (access(cc_params[cc_par_cnt - 1], R_OK))
-        FATAL("-m32 is not supported by your compiler");
+        if (access(cc_params[cc_par_cnt - 1], R_OK))
+          FATAL("-m32 is not supported by your compiler");
 
-      break;
+        break;
 
-    case 64:
-      cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt-64.o", obj_path);
+      case 64:
+        cc_params[cc_par_cnt++] = alloc_printf("%s/afl-llvm-rt-64.o", obj_path);
 
-      if (access(cc_params[cc_par_cnt - 1], R_OK))
-        FATAL("-m64 is not supported by your compiler");
+        if (access(cc_params[cc_par_cnt - 1], R_OK))
+          FATAL("-m64 is not supported by your compiler");
 
-      break;
+        break;
 
+    }
   }
 #endif