diff --git a/doc/gccattributes.h.0.md b/doc/gccattributes.h.0.md
new file mode 100644
index 0000000..d36a6be
--- /dev/null
+++ b/doc/gccattributes.h.0.md
@@ -0,0 +1,21 @@
+% limb manual
+% gccattributes.h(0)
+
+# NAME
+
+gccattributes.h - GCC attributes
+
+# SYNOPSIS
+
+    #include <limb/gccattributes.h>
+
+# DESCRIPTION
+
+This header defines GCC macros to define objects' attributes.
+
+## Macros
+
+The following macros are defined :
+
+: :*gccattr_hidden*
+:: Set visibility to hidden i.e. do not export this symbol.
diff --git a/include/blake3.h b/include/blake3.h
index 29cb678..696984a 100644
--- a/include/blake3.h
+++ b/include/blake3.h
@@ -8,6 +8,7 @@
 #define LIMB_BLAKE3_BLAKE3_H
 
 #include "limb/blake3.h"
+#include "limb/gccattributes.h"
 #include "limb/uint64.h"
 
 /* internal flags */
@@ -155,89 +156,89 @@ store_cv_words(u8 bytes_out[32], u32 cv_words[8])
 
 void blake3_compress_in_place(u32 cv[8],
                               const u8 block[BLAKE3_BLOCK_LEN],
-                              u8 block_len, u64 counter, u8 flags);
+                              u8 block_len, u64 counter, u8 flags) gccattr_hidden;
 
 void blake3_compress_xof(const u32 cv[8],
                          const u8 block[BLAKE3_BLOCK_LEN],
-                         u8 block_len, u64 counter, u8 flags, u8 out[64]);
+                         u8 block_len, u64 counter, u8 flags, u8 out[64]) gccattr_hidden;
 
 void blake3_hash_many(const u8 *const *inputs, size_t num_inputs,
                       size_t blocks, const u32 key[8], u64 counter,
                       char increment_counter, u8 flags,
-                      u8 flags_start, u8 flags_end, u8 *out);
+                      u8 flags_start, u8 flags_end, u8 *out) gccattr_hidden;
 
-size_t blake3_simd_degree(void);
+size_t blake3_simd_degree(void) gccattr_hidden;
 
 
 // Declarations for implementation-specific functions.
 void blake3_compress_in_place_portable(u32 cv[8],
                                        const u8 block[BLAKE3_BLOCK_LEN],
-                                       u8 block_len, u64 counter, u8 flags);
+                                       u8 block_len, u64 counter, u8 flags) gccattr_hidden;
 
 void blake3_compress_xof_portable(const u32 cv[8],
                                   const u8 block[BLAKE3_BLOCK_LEN],
-                                  u8 block_len, u64 counter, u8 flags, u8 out[64]);
+                                  u8 block_len, u64 counter, u8 flags, u8 out[64]) gccattr_hidden;
 
 void blake3_hash_many_portable(const u8 *const *inputs, size_t num_inputs,
                                size_t blocks, const u32 key[8],
                                u64 counter, char increment_counter,
                                u8 flags, u8 flags_start,
-                               u8 flags_end, u8 *out);
+                               u8 flags_end, u8 *out) gccattr_hidden;
 
 #if defined(IS_X86)
 #if !defined(BLAKE3_NO_SSE2)
 void blake3_compress_in_place_sse2(u32 cv[8],
                                    const u8 block[BLAKE3_BLOCK_LEN],
                                    u8 block_len, u64 counter,
-                                   u8 flags);
+                                   u8 flags) gccattr_hidden;
 void blake3_compress_xof_sse2(const u32 cv[8],
                               const u8 block[BLAKE3_BLOCK_LEN],
                               u8 block_len, u64 counter,
-                              u8 flags, u8 out[64]);
+                              u8 flags, u8 out[64]) gccattr_hidden;
 void blake3_hash_many_sse2(const u8 *const *inputs, size_t num_inputs,
                            size_t blocks, const u32 key[8],
                            u64 counter, char increment_counter,
                            u8 flags, u8 flags_start,
-                           u8 flags_end, u8 *out);
+                           u8 flags_end, u8 *out) gccattr_hidden;
 #endif
 #if !defined(BLAKE3_NO_SSE41)
 void blake3_compress_in_place_sse41(u32 cv[8],
                                     const u8 block[BLAKE3_BLOCK_LEN],
                                     u8 block_len, u64 counter,
-                                    u8 flags);
+                                    u8 flags) gccattr_hidden;
 void blake3_compress_xof_sse41(const u32 cv[8],
                                const u8 block[BLAKE3_BLOCK_LEN],
                                u8 block_len, u64 counter,
-                               u8 flags, u8 out[64]);
+                               u8 flags, u8 out[64]) gccattr_hidden;
 void blake3_hash_many_sse41(const u8 *const *inputs, size_t num_inputs,
                             size_t blocks, const u32 key[8],
                             u64 counter, char increment_counter,
                             u8 flags, u8 flags_start,
-                            u8 flags_end, u8 *out);
+                            u8 flags_end, u8 *out) gccattr_hidden;
 #endif
 #if !defined(BLAKE3_NO_AVX2)
 void blake3_hash_many_avx2(const u8 *const *inputs, size_t num_inputs,
                            size_t blocks, const u32 key[8],
                            u64 counter, char increment_counter,
                            u8 flags, u8 flags_start,
-                           u8 flags_end, u8 *out);
+                           u8 flags_end, u8 *out) gccattr_hidden;
 #endif
 #if !defined(BLAKE3_NO_AVX512)
 void blake3_compress_in_place_avx512(u32 cv[8],
                                      const u8 block[BLAKE3_BLOCK_LEN],
                                      u8 block_len, u64 counter,
-                                     u8 flags);
+                                     u8 flags) gccattr_hidden;
 
 void blake3_compress_xof_avx512(const u32 cv[8],
                                 const u8 block[BLAKE3_BLOCK_LEN],
                                 u8 block_len, u64 counter,
-                                u8 flags, u8 out[64]);
+                                u8 flags, u8 out[64]) gccattr_hidden;
 
 void blake3_hash_many_avx512(const u8 *const *inputs, size_t num_inputs,
                              size_t blocks, const u32 key[8],
                              u64 counter, char increment_counter,
                              u8 flags, u8 flags_start,
-                             u8 flags_end, u8 *out);
+                             u8 flags_end, u8 *out) gccattr_hidden;
 #endif
 #endif
 
@@ -246,7 +247,7 @@ void blake3_hash_many_neon(const u8 *const *inputs, size_t num_inputs,
                            size_t blocks, const u32 key[8],
                            u64 counter, char increment_counter,
                            u8 flags, u8 flags_start,
-                           u8 flags_end, u8 *out);
+                           u8 flags_end, u8 *out) gccattr_hidden;
 #endif
 
 
diff --git a/include/hmap.h b/include/hmap.h
index 4f5b570..eca0277 100644
--- a/include/hmap.h
+++ b/include/hmap.h
@@ -6,6 +6,7 @@
 
 #include <errno.h>
 #include "limb/hmap.h"
+#include "limb/gccattributes.h"
 
 #define MINSIZE     8
 #define MAXSIZE     ((u32) -1 / 2 + 1)
@@ -27,7 +28,7 @@ struct item {
 #define DLEN(hmap)          (hmap->ilen - sizeof(u32))
 #define ITEM(i,hmap)        (void *) (hmap->sa.s + (i) * hmap->ilen)
 
-struct item *lookup(u32 key, hmap *hmap);
-int grow(size_t n, hmap *hmap);
+struct item *lookup(u32 key, hmap *hmap) gccattr_hidden;
+int grow(size_t n, hmap *hmap) gccattr_hidden;
 
 #endif /* LIMB_INTERNAL_HMAP_H */
diff --git a/include/limb/gccattributes.h b/include/limb/gccattributes.h
new file mode 100644
index 0000000..48d8014
--- /dev/null
+++ b/include/limb/gccattributes.h
@@ -0,0 +1,17 @@
+/* This file is part of limb                           https://lila.oss/limb
+ * Copyright (C) 2023 Olivier Brunel                          jjk@jjacky.com */
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LIMB_GCCATTRIBUTES_H
+#define LIMB_GCCATTRIBUTES_H
+
+#ifdef __GNUC__
+
+#define gccattr_hidden __attribute__ ((visibility ("hidden")))
+
+#else
+
+#define gccattr_hidden
+
+#endif
+
+#endif /* LIMB_GCCATTRIBUTES_H */
diff --git a/include/loadopt.h b/include/loadopt.h
index 3dfa494..71b5045 100644
--- a/include/loadopt.h
+++ b/include/loadopt.h
@@ -5,6 +5,7 @@
 #define LIMB_LIMB_LOADOPT_H
 
 #include "limb/parseopt.h"
+#include "limb/gccattributes.h"
 
 enum state {
     STATE_NONE = 0,
@@ -25,9 +26,9 @@ enum {
     LOADOPT_EOF         = 1 << 3,
 };
 
-void add_optflags(u8 *optflags, u16 idx, u8 val);
-u8 get_optflags(const u8 *optflags, u16 idx);
+void add_optflags(u8 *optflags, u16 idx, u8 val) gccattr_hidden;
+u8 get_optflags(const u8 *optflags, u16 idx) gccattr_hidden;
 
-int loadopt_handle_noconfig(int idx, const struct option *options, struct loadopt *ctx);
+int loadopt_handle_noconfig(int idx, const struct option *options, struct loadopt *ctx) gccattr_hidden;
 
 #endif /* LIMB_LIMB_LOADOPT_H */
diff --git a/include/sha3/byte_order.h b/include/sha3/byte_order.h
index 1807119..08d0613 100644
--- a/include/sha3/byte_order.h
+++ b/include/sha3/byte_order.h
@@ -7,6 +7,7 @@
 #define BYTE_ORDER_H
 #include <unistd.h>
 #include <stdlib.h>
+#include "limb/gccattributes.h"
 #include "limb/int.h"
 
 #if defined(__GLIBC__)
@@ -120,13 +121,13 @@ extern "C" {
 /* GCC >= 3.4 or clang */
 # define rhash_ctz(x) __builtin_ctz(x)
 #else
-unsigned rhash_ctz(unsigned); /* define as function */
+unsigned rhash_ctz(unsigned) gccattr_hidden; /* define as function */
 #endif
 
-void rhash_swap_copy_str_to_u32(void *to, int index, const void *from, size_t length);
-void rhash_swap_copy_str_to_u64(void *to, int index, const void *from, size_t length);
-void rhash_swap_copy_u64_to_str(void *to, const void *from, size_t length);
-void rhash_u32_mem_swap(unsigned *p, int length_in_u32);
+void rhash_swap_copy_str_to_u32(void *to, int index, const void *from, size_t length); gccattr_hidden
+void rhash_swap_copy_str_to_u64(void *to, int index, const void *from, size_t length); gccattr_hidden
+void rhash_swap_copy_u64_to_str(void *to, const void *from, size_t length); gccattr_hidden
+void rhash_u32_mem_swap(unsigned *p, int length_in_u32); gccattr_hidden
 
 /* bswap definitions */
 #if (defined(__GNUC__) && (__GNUC__ >= 4) && (__GNUC__ > 4 || __GNUC_MINOR__ >= 3)) || \
diff --git a/include/sha3/sha3.h b/include/sha3/sha3.h
index 308698e..0c99824 100644
--- a/include/sha3/sha3.h
+++ b/include/sha3/sha3.h
@@ -6,12 +6,13 @@
 #ifndef LIMB_SHA3_SHA3_H
 #define LIMB_SHA3_SHA3_H
 
+#include "limb/gccattributes.h"
 #include "limb/sha3.h"
 #include "sha3/byte_order.h"
 
 #define SHA3_FINALIZED 0x80000000
 
-void sha3_init(unsigned bits, sha3_ctx *ctx);
-void rhash_sha3_process_block(uint64_t hash[25], const uint64_t *block, size_t block_size);
+void sha3_init(unsigned bits, sha3_ctx *ctx) gccattr_hidden;
+void rhash_sha3_process_block(uint64_t hash[25], const uint64_t *block, size_t block_size) gccattr_hidden;
 
 #endif /* LIMB_SHA3_SHA3_H */