From: Jan Beulich <jbeulich@suse.com>
To: Binutils <binutils@sourceware.org>
Subject: [PATCH v3] x86: avoid i386_dis_printf()'s staging area for a fair part of output
Date: Fri, 26 Aug 2022 12:35:09 +0200 [thread overview]
Message-ID: <9b54f1a3-9aaa-b140-9b33-bade861e89e8@suse.com> (raw)
Message-ID: <20220826103509.ankzwQBUSZKAnWz2SthYZncc7utdw83wOnDsK4lnExU@z> (raw)
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.
---
An alternative to the special casing would be to introduce something
like i386_dis_puts(), then to be used by all call sites which currently
pass "%s" or format strings without any format characters at all (plus,
of course, i386_dis_printf() itself).
---
v3: Change title and description. Re-base over PR binutils/29483 fix.
v2: Add testcase.
--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -9267,31 +9267,40 @@ oappend_register (instr_info *ins, const
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 d
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 d
++curr;
}
while (true);
-
- return res;
}
static int
next reply other threads:[~2022-08-26 10:35 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-26 10:35 Jan Beulich [this message]
2022-08-26 10:35 ` Jan Beulich
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