varasm: Add support for emitting binary data with the new gas .base64 directive

Nick has implemented a new .base64 directive in gas (to be shipped in
the upcoming binutils 2.43; big thanks for that).
See https://sourceware.org/bugzilla/show_bug.cgi?id=31964

The following patch adjusts default_elf_asm_output_ascii (i.e.
ASM_OUTPUT_ASCII elfos.h implementation) to use it if it detects binary
data and gas supports it.

Without this patch, we emit stuff like:
        .string "\177ELF\002\001\001\003"
        .string ""
        .string ""
        .string ""
        .string ""
        .string ""
        .string ""
        .string ""
        .string "\002"
        .string ">"
...
        .string "\324\001\236 0FS\202\002E\n0@\203\004\005&\202\021\337)\021\203C\020A\300\220I\004\t\b\206(\234\0132l\004b\300\bK\006\220$0\303\020P$\233\211\002D\f"
etc., with this patch more compact
        .base64 "f0VMRgIBAQMAAAAAAAAAAAIAPgABAAAAABf3AAAAAABAAAAAAAAAAACneB0AAAAAAAAAAEAAOAAOAEAALAArAAYAAAAEAAAAQAAAAAAAAABAAEAAAAAAAEAAQAAAAAAAEAMAAAAAAAAQAwAAAAAAAAgAAAAAAAAAAwAAAAQAAABQAwAAAAAAAFADQAAAAAAAUANAAAAAAAAcAAAAAAAAABwAAAAAAAAAAQAAAAAAAAABAAAABAAAAAAAAAAAAAAAAABAAAAAAAAAAEAAAAAAADBwOQAAAAAAMHA5AAAAAAAAEAAAAAAAAAEAAAAFAAAAAIA5AAAAAAAAgHkAAAAA"
        .base64 "AACAeQAAAAAAxSSgAgAAAADFJKACAAAAAAAQAAAAAAAAAQAAAAQAAAAAsNkCAAAAAACwGQMAAAAAALAZAwAAAADMtc0AAAAAAMy1zQAAAAAAABAAAAAAAAABAAAABgAAAGhmpwMAAAAAaHbnAwAAAABoducDAAAAAOAMAQAAAAAA4MEeAAAAAAAAEAAAAAAAAAIAAAAGAAAAkH2nAwAAAACQjecDAAAAAJCN5wMAAAAAQAIAAAAAAABAAgAAAAAAAAgAAAAAAAAABAAAAAQAAABwAwAAAAAAAHADQAAAAAAAcANAAAAAAABAAAAAAAAAAEAAAAAAAAAACAAAAAAA"
        .base64 "AAAEAAAABAAAALADAAAAAAAAsANAAAAAAACwA0AAAAAAACAAAAAAAAAAIAAAAAAAAAAEAAAAAAAAAAcAAAAEAAAAaGanAwAAAABoducDAAAAAGh25wMAAAAAAAAAAAAAAAAQAAAAAAAAAAgAAAAAAAAAU+V0ZAQAAABwAwAAAAAAAHADQAAAAAAAcANAAAAAAABAAAAAAAAAAEAAAAAAAAAACAAAAAAAAABQ5XRkBAAAAAw/WAMAAAAADD+YAwAAAAAMP5gDAAAAAPy7CgAAAAAA/LsKAAAAAAAEAAAAAAAAAFHldGQGAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
        .base64 "AAAAAAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAUuV0ZAQAAABoZqcDAAAAAGh25wMAAAAAaHbnAwAAAACYGQAAAAAAAJgZAAAAAAAAAQAAAAAAAAAvbGliNjQvbGQtbGludXgteDg2LTY0LnNvLjIAAAAAAAQAAAAwAAAABQAAAEdOVQACgADABAAAAAEAAAAAAAAAAQABwAQAAAAJAAAAAAAAAAIAAcAEAAAAAwAAAAAAAAAEAAAAEAAAAAEAAABHTlUAAAAAAAMAAAACAAAAAAAAAAOAAACsqAAAgS0AAOJWAAAjNwAAXjAAAAAAAAAAAAAAF1gAAHsxAABBBwAA"
        .base64 "G0kAALGmAACwoAAAAAAAAAAAAACQhAAAAAAAAOw1AACNYgAAAAAAAFQoAAAAAAAAx3UAALZAAAAAAAAAiIUAALGeAABBlAAAWEsAAPmRAACmOgAAAAAAADh3AAAAAAAAlCAAAAAAAABymgAAaosAAMIjAAAKMQAAMkIAADU0AAAAAAAA5ZwAAAAAAAAAAAAAAAAAAFIdAAAIGQAAAAAAAMFbAAAoTQAAGDcAAIRgAAA6HgAAlxwAAAAAAADOlgAAAAAAAEhPAAARiwAAMGgAAOVtAADMFgAAAAAAAAAAAACrjgAAYl4AACZVAAA/HgAAAAAAAAAAAABqPwAAAAAA"
The patch attempts to juggle between readability and compactness, so
if it detects some hunk of the initializer that would be shorter to be
emitted as .string/.ascii directive, it does so, but if it previously
used .base64 directive it switches mode only if there is a 16+ char
ASCII-ish string.

On my #embed testcase from yesterday
unsigned char a[] = {
 #embed "cc1plus"
};
without this patch it emits 2.4GB of assembly, while with this
patch 649M.
Compile times (trunk, so yes,rtl,extra checking) are:
time ./xgcc -B ./ -S -std=c23 -O2 embed-11.c

real    0m13.647s
user    0m7.157s
sys     0m2.597s
time ./xgcc -B ./ -c -std=c23 -O2 embed-11.c

real    0m28.649s
user    0m26.653s
sys     0m1.958s
without the patch and
time ./xgcc -B ./ -S -std=c23 -O2 embed-11.c

real    0m4.283s
user    0m2.288s
sys     0m0.859s
time ./xgcc -B ./ -c -std=c23 -O2 embed-11.c

real    0m6.888s
user    0m5.876s
sys     0m1.002s
with the patch, so that feels like significant improvement.
The resulting embed-11.o is identical between the two ways of expressing
the mostly binary data in the assembly.  But note that there are portions
like:
        .base64 "nAAAAAAAAAAvZRcAIgAOAFAzMwEAAAAABgAAAAAAAACEQBgAEgAOAFBHcAIAAAAA7AAAAAAAAAAAX19nbXB6X2dldF9zaQBtcGZyX3NldF9zaV8yZXhwAG1wZnJfY29zaABtcGZyX3RhbmgAbXBmcl9zZXRfbmFuAG1wZnJfc3ViAG1wZnJfdGFuAG1wZnJfc3RydG9mcgBfX2dtcHpfc3ViX3VpAF9fZ21wX2dldF9tZW1vcnlfZnVuY3Rpb25zAF9fZ21wel9zZXRfdWkAbXBmcl9wb3cAX19nbXB6X3N1YgBfX2dtcHpfZml0c19zbG9uZ19wAG1wZnJfYXRh"
        .base64 "bjIAX19nbXB6X2RpdmV4YWN0AG1wZnJfc2V0X2VtaW4AX19nbXB6X3NldABfX2dtcHpfbXVsAG1wZnJfY2xlYXIAbXBmcl9sb2cAbXBmcl9hdGFuaABfX2dtcHpfc3dhcABtcGZyX2FzaW5oAG1wZnJfYXNpbgBtcGZyX2NsZWFycwBfX2dtcHpfbXVsXzJleHAAX19nbXB6X2FkZG11bABtcGZyX3NpbmgAX19nbXB6X2FkZF91aQBfX2dtcHFfY2xlYXIAX19nbW9uX3N0YXJ0X18AbXBmcl9hY29zAG1wZnJfc2V0X2VtYXgAbXBmcl9jb3MAbXBmcl9zaW4A"
        .string "__gmpz_ui_pow_ui"
        .string "mpfr_get_str"
        .string "mpfr_acosh"
        .string "mpfr_sub_ui"
        .string "__gmpq_set_ui"
        .string "mpfr_set_inf"
...
        .string "GLIBC_2.14"
        .string "GLIBC_2.11"
        .base64 "AAABAAIAAQADAAMAAwADAAMAAwAEAAUABgADAAEAAQADAAMABwABAAEAAwADAAMAAwAIAAEAAwADAAEAAwABAAMAAwABAAMAAQADAAMAAwADAAMAAwADAAYAAwADAAEAAQAIAAMAAwADAAMAAwABAAMAAQADAAMAAQABAAEAAwAIAAEAAwADAAEAAwABAAMAAQADAAEABgADAAMAAQAHAAMAAwADAAMAAwABAAMAAQABAAMAAwADAAkAAQABAAEAAwAKAAEAAwADAAMAAQABAAMAAwALAAEAAwADAAEAAQADAAMAAwABAAMAAwABAAEAAwADAAMABwABAAMAAwAB"
        .base64 "AAEAAwADAAEAAwABAAMAAQADAAMAAwADAAEAAQABAAEAAwADAAMAAQABAAEAAQABAAEAAQADAAMAAwADAAMAAQABAAwAAwADAA0AAwADAAMAAwADAAEAAQADAAMAAQABAAMAAwADAAEAAwADAAEAAwAIAAMAAwADAAMABgABAA4ACwAGAAEAAQADAAEAAQADAAEAAwABAAMAAwABAAEAAwABAAMAAwABAAEAAwADAAMAAwABAAMAAQABAAEAAQABAAMADwABAAMAAQADAAMAAwABAAEAAQAIAAEADAADAAMAAQABAAMAAwADAAEAAQABAAEAAQADAAEAAwADAAEA"
        .base64 "AwABAAMAAQADAAMAAQABAAEAAwADAAMAAwADAAMAAQADAAMACAAQAA8AAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQABAAEAAQA="
so it isn't all just totally unreadable stuff.

2024-07-15  Jakub Jelinek  <jakub@redhat.com>

	* configure.ac (HAVE_GAS_BASE64): New check.
	* config/elfos.h (BASE64_ASM_OP): Define if HAVE_GAS_BASE64 is
	defined.
	* varasm.cc (assemble_string): Bump maximum from 2000 to 16384 if
	BASE64_ASM_OP is defined.
	(default_elf_asm_output_limited_string): Emit opening '"' together
	with STRING_ASM_OP.
	(default_elf_asm_output_ascii): Use BASE64_ASM_OP if defined and
	beneficial.  Remove UB when last_null is NULL.
	* configure: Regenerate.
	* config.in: Regenerate.

5 files changed, 162 insertions, 3 deletions

diff --git a/gcc/config.in b/gcc/config.in
index ae41596..bc81900 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -1437,6 +1437,12 @@
 #endif
 
 
+/* Define if your assembler supports .base64. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_BASE64
+#endif
+
+
 /* Define 0/1 if your assembler supports CFI directives. */
 #undef HAVE_GAS_CFI_DIRECTIVE
 
diff --git a/gcc/config/elfos.h b/gcc/config/elfos.h
index da45593..1338815 100644
--- a/gcc/config/elfos.h
+++ b/gcc/config/elfos.h
@@ -444,6 +444,10 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 
 #define STRING_ASM_OP	"\t.string\t"
 
+#ifdef HAVE_GAS_BASE64
+#define BASE64_ASM_OP	"\t.base64\t"
+#endif
+
 /* The routine used to output NUL terminated strings.  We use a special
    version of this for most svr4 targets because doing so makes the
    generated assembly code more compact (and thus faster to assemble)
diff --git a/gcc/configure b/gcc/configure
index 1335db2..4faae0f 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -25859,6 +25859,39 @@ case "${target}" in
     ;;
 esac
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for .base64" >&5
+$as_echo_n "checking assembler for .base64... " >&6; }
+if ${gcc_cv_as_base64+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_base64=no
+  if test x$gcc_cv_as != x; then
+    $as_echo '	.section .rodata
+ 	.base64 "Tm9uIHB1ZG9yIGVzdCBuaWwgc2NpcmUsIHB1ZG9yIG5pbCBkaXNjZXJlIHZlbGxlLgo="' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags  -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+	gcc_cv_as_base64=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_as_base64" >&5
+$as_echo "$gcc_cv_as_base64" >&6; }
+if test $gcc_cv_as_base64 = yes; then
+
+$as_echo "#define HAVE_GAS_BASE64 1" >>confdefs.h
+
+fi
+
+
 # gnu_indirect_function type is an extension proposed at
 # http://groups.google/com/group/generic-abi/files. It allows dynamic runtime
 # selection of function implementation
diff --git a/gcc/configure.ac b/gcc/configure.ac
index eb72f65..3da1eaa 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -3054,6 +3054,11 @@ case "${target}" in
     ;;
 esac
 
+gcc_GAS_CHECK_FEATURE([.base64], gcc_cv_as_base64,,
+ [	.section .rodata
+ 	.base64 "Tm9uIHB1ZG9yIGVzdCBuaWwgc2NpcmUsIHB1ZG9yIG5pbCBkaXNjZXJlIHZlbGxlLgo="],,
+[AC_DEFINE(HAVE_GAS_BASE64, 1, [Define if your assembler supports .base64.])])
+
 # gnu_indirect_function type is an extension proposed at
 # http://groups.google/com/group/generic-abi/files. It allows dynamic runtime
 # selection of function implementation
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index a6ef099..fe0a6b8 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -2101,7 +2101,19 @@ void
 assemble_string (const char *p, int size)
 {
   int pos = 0;
+#if defined(BASE64_ASM_OP) \
+    && BITS_PER_UNIT == 8 \
+    && CHAR_BIT == 8 \
+    && 'A' == 65 \
+    && 'a' == 97 \
+    && '0' == 48 \
+    && '+' == 43 \
+    && '/' == 47 \
+    && '=' == 61
+  int maximum = 16384;
+#else
   int maximum = 2000;
+#endif
 
   /* If the string is very long, split it up.  */
 
@@ -8454,8 +8466,7 @@ default_elf_asm_output_limited_string (FILE *f, const char *s)
   int escape;
   unsigned char c;
 
-  fputs (STRING_ASM_OP, f);
-  putc ('"', f);
+  fputs (STRING_ASM_OP "\"", f);
   while (*s != '\0')
     {
       c = *s;
@@ -8489,9 +8500,11 @@ default_elf_asm_output_ascii (FILE *f, const char *s, unsigned int len)
 {
   const char *limit = s + len;
   const char *last_null = NULL;
+  const char *last_base64 = s;
   unsigned bytes_in_chunk = 0;
   unsigned char c;
   int escape;
+  bool prev_base64 = false;
 
   for (; s < limit; s++)
     {
@@ -8504,7 +8517,7 @@ default_elf_asm_output_ascii (FILE *f, const char *s, unsigned int len)
 	  bytes_in_chunk = 0;
 	}
 
-      if (s > last_null)
+      if ((uintptr_t) s > (uintptr_t) last_null)
 	{
 	  for (p = s; p < limit && *p != '\0'; p++)
 	    continue;
@@ -8513,6 +8526,104 @@ default_elf_asm_output_ascii (FILE *f, const char *s, unsigned int len)
       else
 	p = last_null;
 
+#if defined(BASE64_ASM_OP) \
+    && BITS_PER_UNIT == 8 \
+    && CHAR_BIT == 8 \
+    && 'A' == 65 \
+    && 'a' == 97 \
+    && '0' == 48 \
+    && '+' == 43 \
+    && '/' == 47 \
+    && '=' == 61
+      if (s >= last_base64)
+	{
+	  unsigned cnt = 0;
+	  const char *t;
+	  for (t = s; t < limit && (t - s) < (long) ELF_STRING_LIMIT - 1; t++)
+	    {
+	      if (t == p && t != s)
+		{
+		  if (cnt <= (t - s + 1 + 2) / 3 * 4
+		      && (!prev_base64 || (t - s) >= 16)
+		      && ((t - s) > 1 || cnt <= 2))
+		    {
+		      last_base64 = p;
+		      goto no_base64;
+		    }
+		}
+	      c = *t;
+	      escape = ELF_ASCII_ESCAPES[c];
+	      switch (escape)
+		{
+		case 0:
+		  ++cnt;
+		  break;
+		case 1:
+		  if (c == 0)
+		    cnt += 2 + strlen (STRING_ASM_OP) + 1;
+		  else
+		    cnt += 4;
+		  break;
+		default:
+		  cnt += 2;
+		  break;
+		}
+	    }
+	  if (cnt > (t - s + 2) / 3 * 4 && (t - s) >= 3)
+	    {
+	      if (bytes_in_chunk > 0)
+		{
+		  putc ('\"', f);
+		  putc ('\n', f);
+		  bytes_in_chunk = 0;
+		}
+
+	      unsigned char buf[(ELF_STRING_LIMIT + 2) / 3 * 4 + 3];
+	      unsigned j = 0;
+	      static const char base64_enc[] =
+		"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+		"0123456789+/";
+
+	      fputs (BASE64_ASM_OP "\"", f);
+	      while (s < t)
+		{
+		  unsigned char a = *s;
+		  unsigned char b = 0, c = 0;
+		  if (s < t - 1)
+		    b = s[1];
+		  if (s < t - 2)
+		    c = s[2];
+		  unsigned long v = ((((unsigned long) a) << 16)
+				     | (((unsigned long) b) << 8)
+				     | c);
+		  buf[j++] = base64_enc[(v >> 18) & 63];
+		  buf[j++] = base64_enc[(v >> 12) & 63];
+		  buf[j++] = base64_enc[(v >> 6) & 63];
+		  buf[j++] = base64_enc[v & 63];
+		  if (s >= t - 2)
+		    {
+		      buf[j - 1] = '=';
+		      if (s >= t - 1)
+			buf[j - 2] = '=';
+		      break;
+		    }
+		  s += 3;
+		}
+	      memcpy (buf + j, "\"\n", 3);
+	      fputs ((const char *) buf, f);
+	      s = t - 1;
+	      prev_base64 = true;
+	      continue;
+	    }
+	  last_base64 = t;
+	no_base64:
+	  prev_base64 = false;
+	}
+#else
+      (void) last_base64;
+      (void) prev_base64;
+#endif
+
       if (p < limit && (p - s) <= (long) ELF_STRING_LIMIT)
 	{
 	  if (bytes_in_chunk > 0)