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Re: [RFA 4/6] Simple cleanup removals in remote.c
On 10/16/2017 10:36 PM, Simon Marchi wrote:
> On 2017-10-16 05:14 PM, Tom Tromey wrote:
>>>>>>> "Simon" == Simon Marchi <simon.marchi@ericsson.com> writes:
>>
>> Simon> For this one, wouldn't it be easier to just go with a string? Something like:
>>
>> It's easier but less efficient.
>> I wasn't sure if it mattered so I erred on the side of efficiency.
>>
>> Tom
>>
>
> I suppose you are talking about the += string_printf ()? It's true that it's
> not the most efficient, because the formatting is done in a separate buffer
> (an std::string) and then copied, instead of directly in-place. At least,
> there's likely no dynamic memory allocation, because the string fits in
> std::string's local buffer.
This suggests to me that we're missing a string_printf variant that
appends to a preexisting string:
void string_appendf (std::string &dest, const char* fmt, ...);
See (untested) patch below.
>
> So since there's likely no real-world impact, I would've erred on the other
> side.
>
> In any case, I don't really mind, your version is good too and eliminates the
> clean up, which is the main point.
I agree. Tom, please go ahead.
>From e9602dc6ee8eac1f0dc5b267e961f9a206ce649b Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Mon, 16 Oct 2017 23:22:27 +0100
Subject: [PATCH] string_appendf
---
gdb/common/common-utils.c | 22 ++++++++++++++++++++++
gdb/common/common-utils.h | 5 +++++
gdb/remote.c | 22 +++++++---------------
3 files changed, 34 insertions(+), 15 deletions(-)
diff --git a/gdb/common/common-utils.c b/gdb/common/common-utils.c
index d8c546a..8ca62f3 100644
--- a/gdb/common/common-utils.c
+++ b/gdb/common/common-utils.c
@@ -153,6 +153,28 @@ xsnprintf (char *str, size_t size, const char *format, ...)
/* See documentation in common-utils.h. */
+void
+string_appendf (std::string &str, const char* fmt, ...)
+{
+ va_list vp;
+ int grow_size;
+
+ va_start (vp, fmt);
+ grow_size = vsnprintf (NULL, 0, fmt, vp);
+ va_end (vp);
+
+ size_t curr_size = str.size ();
+ str.resize (curr_size + grow_size);
+
+ /* C++11 and later guarantee std::string uses contiguous memory and
+ always includes the terminating '\0'. */
+ va_start (vp, fmt);
+ vsprintf (&str[curr_size], fmt, vp);
+ va_end (vp);
+}
+
+/* See documentation in common-utils.h. */
+
std::string
string_printf (const char* fmt, ...)
{
diff --git a/gdb/common/common-utils.h b/gdb/common/common-utils.h
index 19724f9..bf1b444 100644
--- a/gdb/common/common-utils.h
+++ b/gdb/common/common-utils.h
@@ -67,6 +67,11 @@ std::string string_printf (const char* fmt, ...)
std::string string_vprintf (const char* fmt, va_list args)
ATTRIBUTE_PRINTF (1, 0);
+/* Like string_printf, but appends to dest instead of returning a new
+ std::string. */
+void string_appendf (std::string &dest, const char* fmt, ...)
+ ATTRIBUTE_PRINTF (2, 3);
+
/* Make a copy of the string at PTR with LEN characters
(and add a null character at the end in the copy).
Uses malloc to get the space. Returns the address of the copy. */
diff --git a/gdb/remote.c b/gdb/remote.c
index 6b77a9f..a6cb724 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -2086,40 +2086,32 @@ remote_set_syscall_catchpoint (struct target_ops *self,
pid, needed, any_count, n_sysno);
}
- gdb::unique_xmalloc_ptr<char> built_packet;
+ std::string built_packet;
if (needed)
{
/* Prepare a packet with the sysno list, assuming max 8+1
characters for a sysno. If the resulting packet size is too
big, fallback on the non-selective packet. */
const int maxpktsz = strlen ("QCatchSyscalls:1") + n_sysno * 9 + 1;
-
- built_packet.reset ((char *) xmalloc (maxpktsz));
- strcpy (built_packet.get (), "QCatchSyscalls:1");
+ built_packet.reserve (maxpktsz);
+ built_packet = "QCatchSyscalls:1";
if (!any_count)
{
- int i;
- char *p;
-
- p = built_packet.get ();
- p += strlen (p);
-
/* Add in catch_packet each syscall to be caught (table[i] != 0). */
- for (i = 0; i < table_size; i++)
+ for (int i = 0; i < table_size; i++)
{
if (table[i] != 0)
- p += xsnprintf (p, built_packet.get () + maxpktsz - p,
- ";%x", i);
+ string_appendf (built_packet, ";%x", i);
}
}
- if (strlen (built_packet.get ()) > get_remote_packet_size ())
+ if (built_packet.size () > get_remote_packet_size ())
{
/* catch_packet too big. Fallback to less efficient
non selective mode, with GDB doing the filtering. */
catch_packet = "QCatchSyscalls:1";
}
else
- catch_packet = built_packet.get ();
+ catch_packet = built_packet.c_str ();
}
else
catch_packet = "QCatchSyscalls:0";
--
2.5.5