[binutils-gdb] x86: avoid i386_dis_printf()'s staging area for a fair part of output

[binutils-gdb] x86: avoid i386_dis_printf()'s staging area for a fair part of output

[Jan Beulich]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ac3fe48fd61a92d03c66152038df4fc184bf5fcd

commit ac3fe48fd61a92d03c66152038df4fc184bf5fcd
Author: Jan Beulich <jbeulich@suse.com>
Date:   Mon Sep 12 08:19:55 2022 +0200

    x86: avoid i386_dis_printf()'s staging area for a fair part of output
    
    While PR binutils/29483 has now been addressed differently, this
    originally proposed change still has its merits: Avoiding vsnprintf()
    for typically far more than half of the overall output results in a 2-3%
    performance gain in my testing (with debug builds of objdump, libbfd,
    and libopcodes).
    
    With that part of output no longer using staging_area[], the array also
    doesn't need to be quite as large anymore (the largest presently used
    size is 27, from "64-bit address is disabled").
    
    While limiting the scope of "res" it became apparent that
    - no caller cares about the function's return value,
    - the comment about the return value was wrong,
    - a particular positive return value would have been meaningless to the
      caller.
    Therefore convert the function to return "void" at the same time.

Diff:
---
 opcodes/i386-dis.c | 44 ++++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/opcodes/i386-dis.c b/opcodes/i386-dis.c
index c1166a4446c..98d3ecd9f05 100644
--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -9267,31 +9267,40 @@ oappend_register (instr_info *ins, const char *s)
    STYLE is the default style to use in the fprintf_styled_func calls,
    however, FMT might include embedded style markers (see oappend_style),
    these embedded markers are not printed, but instead change the style
-   used in the next fprintf_styled_func call.
+   used in the next fprintf_styled_func call.  */
 
-   Return non-zero to indicate the print call was a success.  */
-
-static int ATTRIBUTE_PRINTF_3
+static void ATTRIBUTE_PRINTF_3
 i386_dis_printf (instr_info *ins, enum disassembler_style style,
 		 const char *fmt, ...)
 {
   va_list ap;
   enum disassembler_style curr_style = style;
-  char *start, *curr;
-  char staging_area[MAX_OPERAND_BUFFER_SIZE];
-  int res;
+  const char *start, *curr;
+  char staging_area[40];
 
   va_start (ap, fmt);
-  res = vsnprintf (staging_area, sizeof (staging_area), fmt, ap);
-  va_end (ap);
+  /* In particular print_insn()'s processing of op_txt[] can hand rather long
+     strings here.  Bypass vsnprintf() in such cases to avoid capacity issues
+     with the staging area.  */
+  if (strcmp (fmt, "%s"))
+    {
+      int res = vsnprintf (staging_area, sizeof (staging_area), fmt, ap);
 
-  if (res < 0)
-    return res;
+      va_end (ap);
 
-  if ((size_t) res >= sizeof (staging_area))
-    abort ();
+      if (res < 0)
+	return;
 
-  start = curr = staging_area;
+      if ((size_t) res >= sizeof (staging_area))
+	abort ();
+
+      start = curr = staging_area;
+    }
+  else
+    {
+      start = curr = va_arg (ap, const char *);
+      va_end (ap);
+    }
 
   do
     {
@@ -9306,10 +9315,7 @@ i386_dis_printf (instr_info *ins, enum disassembler_style style,
 						     curr_style,
 						     "%.*s", len, start);
 	  if (n < 0)
-	    {
-	      res = n;
-	      break;
-	    }
+	    break;
 
 	  if (*curr == '\0')
 	    break;
@@ -9343,8 +9349,6 @@ i386_dis_printf (instr_info *ins, enum disassembler_style style,
 	++curr;
     }
   while (true);
-
-  return res;
 }
 
 static int