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Date: Sun, 27 Dec 2020 18:53:01 +0100
From: Charlotte Delenk <>
Subject: [PATCH] Add support for LLVM's Control Flow Integrity


I have attempted to use musl HEAD together with clang's -fsanitize=cfi,
but currently it requires the main function to take all 3 arguments and
return an int.

After this patch is applied, clang will no longer try to add CFI
sanitization to the libc_start_main_stage2 function, allowing programs
to get to main().

I have tested CFI sanitization for both regular indirect functions
(qsort()) and thread creation and validly typed function pointers cause
no runtime aborts with CFI enabled for the whole program.


  src/env/__libc_start_main.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/src/env/__libc_start_main.c b/src/env/__libc_start_main.c
index 8fbe5262..af61fb7c 100644
--- a/src/env/__libc_start_main.c
+++ b/src/env/__libc_start_main.c
@@ -85,6 +85,9 @@ int __libc_start_main(int (*main)(int,char **,char 
**), int argc, char **argv)
      return stage2(main, argc, argv);

+#ifdef __clang__
  static int libc_start_main_stage2(int (*main)(int,char **,char **), 
int argc, char **argv)
      char **envp = argv+argc+1;

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