crypto/gc-sm3: fix compilation error with --with-libgcrypt

[Bruno Haible <bruno@clisp.org>]

This fails:
$ ./gnulib-tool --create-testdir --dir=../testdir1 --single-configure crypto/gc-sm3
$ cd ../testdir1
$ ./configure --with-libgcrypt
$ make
...
gc-libgcrypt.c: In function 'gc_hash_open':
gc-libgcrypt.c:309:17: error: 'GCRY_MD_SM3' undeclared (first use in this function)
       gcryalg = GCRY_MD_SM3;
                 ^
gc-libgcrypt.c:309:17: note: each undeclared identifier is reported only once for each function it appears in
gc-libgcrypt.c: In function 'gc_hash_buffer':
gc-libgcrypt.c:545:17: error: 'GCRY_MD_SM3' undeclared (first use in this function)
       gcryalg = GCRY_MD_SM3;
                 ^
gc-libgcrypt.c: In function 'gc_sm3':
gc-libgcrypt.c:669:42: error: 'GCRY_MD_SM3' undeclared (first use in this function)
   size_t outlen = gcry_md_get_algo_dlen (GCRY_MD_SM3);
                                          ^
Makefile:640: recipe for target 'gc-libgcrypt.o' failed
make[4]: *** [gc-libgcrypt.o] Error 1

I'm using libgcrypt 1.6.5.


This patch fixes it. It follows the coding idiom for md2 (which is also present
in gnulib but not in libgcrypt), but leaves open the possibility that sm3
supports gets added in a future version of libgcrypt. AFAICS, it is scheduled
for inclusion in libgcrypt 1.9.


2019-08-24  Bruno Haible  <bruno@clisp.org>

	crypto/gc-sm3: Fix compilation error with --with-libgcrypt.
	* m4/gc-sm3.m4 (gl_GC_SM3): Test whether libgcrypt supports SM3. Define
	LIBGCRYPT_HAS_MD_SM3.
	* lib/gc-libgcrypt.c: Include sm3.h.
	(_gc_hash_ctx, gc_hash_open, gc_hash_hmac_setkey, gc_hash_write,
	gc_hash_read, gc_hash_close, gc_hash_buffer, gc_sm3): Use the gnulib
	implementation if libgcrypt does not support SM3.

diff --git a/lib/gc-libgcrypt.c b/lib/gc-libgcrypt.c
index fbfd0a1..3ca17c2 100644
--- a/lib/gc-libgcrypt.c
+++ b/lib/gc-libgcrypt.c
@@ -33,6 +33,9 @@
    MD2 algorithm.  Therefore take the implementation from gnulib.  */
 # include "md2.h"
 #endif
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+# include "sm3.h"
+#endif
 
 #include <assert.h>
 
@@ -243,14 +246,22 @@ gc_cipher_close (gc_cipher_handle handle)
 
 /* Hashes. */
 
+/* Maximum of GC_MD2_DIGEST_SIZE and GC_SM3_DIGEST_SIZE.  */
+#define MAX_DIGEST_SIZE 32
+
 typedef struct _gc_hash_ctx {
   Gc_hash alg;
   Gc_hash_mode mode;
   gcry_md_hd_t gch;
+#if GNULIB_GC_MD2 || (GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3)
+  char hash[MAX_DIGEST_SIZE];
+#endif
 #if GNULIB_GC_MD2
-  char hash[GC_MD2_DIGEST_SIZE];
   struct md2_ctx md2Context;
 #endif
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+  struct sm3_ctx sm3Context;
+#endif
 } _gc_hash_ctx;
 
 Gc_rc
@@ -312,7 +323,12 @@ gc_hash_open (Gc_hash hash, Gc_hash_mode mode, gc_hash_handle * outhandle)
 
 #if GNULIB_GC_SM3
     case GC_SM3:
+# if LIBGCRYPT_HAS_MD_SM3
       gcryalg = GCRY_MD_SM3;
+# else
+      sm3_init_ctx (&ctx->sm3Context);
+      gcryalg = GCRY_MD_NONE;
+# endif
       break;
 #endif
 
@@ -433,7 +449,10 @@ gc_hash_hmac_setkey (gc_hash_handle handle, size_t len, const char *key)
 #if GNULIB_GC_MD2
   if (ctx->alg != GC_MD2)
 #endif
-    gcry_md_setkey (ctx->gch, key, len);
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+    if (ctx->alg != GC_SM3)
+#endif
+      gcry_md_setkey (ctx->gch, key, len);
 }
 
 void
@@ -446,6 +465,11 @@ gc_hash_write (gc_hash_handle handle, size_t len, const char *data)
     md2_process_bytes (data, len, &ctx->md2Context);
   else
 #endif
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+  if (ctx->alg == GC_SM3)
+    sm3_process_bytes (data, len, &ctx->sm3Context);
+  else
+#endif
     gcry_md_write (ctx->gch, data, len);
 }
 
@@ -463,6 +487,14 @@ gc_hash_read (gc_hash_handle handle)
     }
   else
 #endif
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+  if (ctx->alg == GC_SM3)
+    {
+      sm3_finish_ctx (&ctx->sm3Context, ctx->hash);
+      digest = ctx->hash;
+    }
+  else
+#endif
     {
       gcry_md_final (ctx->gch);
       digest = (const char *) gcry_md_read (ctx->gch, 0);
@@ -479,7 +511,10 @@ gc_hash_close (gc_hash_handle handle)
 #if GNULIB_GC_MD2
   if (ctx->alg != GC_MD2)
 #endif
-    gcry_md_close (ctx->gch);
+#if GNULIB_GC_SM3 && !LIBGCRYPT_HAS_MD_SM3
+    if (ctx->alg != GC_SM3)
+#endif
+      gcry_md_close (ctx->gch);
 
   free (ctx);
 }
@@ -495,7 +530,6 @@ gc_hash_buffer (Gc_hash hash, const void *in, size_t inlen, char *resbuf)
     case GC_MD2:
       md2_buffer (in, inlen, resbuf);
       return GC_OK;
-      break;
 #endif
 
 #if GNULIB_GC_MD4
@@ -548,8 +582,13 @@ gc_hash_buffer (Gc_hash hash, const void *in, size_t inlen, char *resbuf)
 
 #if GNULIB_GC_SM3
     case GC_SM3:
+# if !LIBGCRYPT_HAS_MD_SM3
+      sm3_buffer (in, inlen, resbuf);
+      return GC_OK;
+# else
       gcryalg = GCRY_MD_SM3;
       break;
+# endif
 #endif
 
     default:
@@ -672,6 +711,10 @@ gc_sha1 (const void *in, size_t inlen, void *resbuf)
 Gc_rc
 gc_sm3  (const void *in, size_t inlen, void *resbuf)
 {
+# if !LIBGCRYPT_HAS_MD_SM3
+  sm3_buffer (in, inlen, resbuf);
+  return GC_OK;
+# else
   size_t outlen = gcry_md_get_algo_dlen (GCRY_MD_SM3);
   gcry_md_hd_t hd;
   gpg_error_t err;
@@ -697,6 +740,7 @@ gc_sm3  (const void *in, size_t inlen, void *resbuf)
   gcry_md_close (hd);
 
   return GC_OK;
+# endif
 }
 #endif
 
diff --git a/m4/gc-sm3.m4 b/m4/gc-sm3.m4
index 7eac448..992217d 100644
--- a/m4/gc-sm3.m4
+++ b/m4/gc-sm3.m4
@@ -1,4 +1,4 @@
-# gc-sm3.m4 serial 1
+# gc-sm3.m4 serial 2
 dnl Copyright (C) 2017-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,4 +7,19 @@ dnl with or without modifications, as long as this notice is preserved.
 AC_DEFUN([gl_GC_SM3],
 [
   AC_REQUIRE([gl_GC])
+  AC_CACHE_CHECK([whether libgcrypt supports SM3],
+    [gl_cv_libcrypt_md_sm3],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM([[
+          #include <gcrypt.h>
+          int a = GCRY_MD_SM3;
+          ]], [[]])
+       ],
+       [gl_cv_libcrypt_md_sm3=yes],
+       [gl_cv_libcrypt_md_sm3=no])
+    ])
+  if test $gl_cv_libcrypt_md_sm3 = yes; then
+    AC_DEFINE([LIBGCRYPT_HAS_MD_SM3], [1],
+      [Define if libgcrypt supports the MD algorithm SM3.])
+  fi
 ])