From 9964edfb4abdec25f8be48e667afcae30ce03a37 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Mon, 15 Jul 2024 09:48:38 +0200
Subject: [PATCH] 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.
---
gcc/config.in | 6 +++
gcc/config/elfos.h | 4 ++
gcc/configure | 33 +++++++++++++
gcc/configure.ac | 5 ++
gcc/varasm.cc | 117 +++++++++++++++++++++++++++++++++++++++++++--
5 files changed, 162 insertions(+), 3 deletions(-)
diff --git a/gcc/config.in b/gcc/config.in
index ae41596596fa..bc819005bd62 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 da45593fb305..133881509df2 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 1335db2d4d2e..4faae0fa5fb8 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 eb72f65865ab..3da1eaa70646 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 a6ef099c3641..fe0a6b873ef4 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)
--
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