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Always allow linking AFL-instrumented modules #10107

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Jan 4, 2021
Merged

Always allow linking AFL-instrumented modules #10107

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4 changes: 4 additions & 0 deletions Changes
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Expand Up @@ -269,6 +269,10 @@ OCaml 4.12.0
- #10062: set ARCH_INT64_PRINTF_FORMAT correctly for both modes of mingw-w64
(David Allsopp, review by Xavier Leroy)

- #10107: Ensure modules compiled with -afl-instrument can still link on
platforms without AFL support.
(David Allsopp, review by ???)

### Code generation and optimizations:

- #9551: ocamlc no longer loads DLLs at link time to check that
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16 changes: 11 additions & 5 deletions runtime/afl.c
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Expand Up @@ -15,6 +15,11 @@
/* Runtime support for afl-fuzz */
#include "caml/config.h"

/* Values used by the instrumentation logic (see cmmgen.ml) */
static unsigned char afl_area_initial[1 << 16];
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So, every OCaml program is 64 Kbytes bigger, just in case AFL is applied to it?

I know this is orthogonal to the issue at hand, but I'd really like to see on-demand allocation here.

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Ah, it wasn't just me bothered by this! I'll open an issue to track it...

unsigned char* caml_afl_area_ptr = afl_area_initial;
uintnat caml_afl_prev_loc;

#if !defined(HAS_SYS_SHM_H) || !defined(HAS_SHMAT)

#include "caml/mlvalues.h"
Expand All @@ -24,6 +29,12 @@ CAMLprim value caml_reset_afl_instrumentation(value full)
return Val_unit;
}

CAMLexport value caml_setup_afl(value unit)
{
/* AFL is not supported */
return Val_unit;
}

#else

#include <unistd.h>
Expand All @@ -45,11 +56,6 @@ static int afl_initialised = 0;
to count a testcase as "crashing" */
extern int caml_abort_on_uncaught_exn;

/* Values used by the instrumentation logic (see cmmgen.ml) */
static unsigned char afl_area_initial[1 << 16];
unsigned char* caml_afl_area_ptr = afl_area_initial;
uintnat caml_afl_prev_loc;

/* File descriptors used to synchronise with afl-fuzz */
#define FORKSRV_FD_READ 198
#define FORKSRV_FD_WRITE 199
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