Re: [PATCH 2/2] Find the next matched trace file in 'tfile target'.

Pedro Alves
2013-02-26T19:53:16Z

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On 02/25/2013 02:57 AM, Yao Qi wrote:
> The previous patch exposes a bug in tfile target when finding a trace
> frame. Every time, GDB will scan tfile from the starting offset and
> initialize trace frame number to zero. When TYPE is not tfind_number,
> it means GDB wants to find the *next* matched trace frame of current
> one. So we need to check the tfile trace frame number iterator is
> greater than the current trace frame number (which means *next*).
> This is mainly what this patch does.

Thanks. Good catch.

> diff --git a/gdb/tracepoint.c b/gdb/tracepoint.c
> index ca104aa..f7a3650 100644
> --- a/gdb/tracepoint.c
> +++ b/gdb/tracepoint.c
> @@ -4324,22 +4324,34 @@ tfile_trace_find (enum trace_find_type type, int num,
> break;
> case tfind_pc:
> tfaddr = tfile_get_traceframe_address (tframe_offset);
> - if (tfaddr == addr1)
> + if (tfaddr == addr1
> + /* Looks for the next trace frame if matched. */
> + && (tfnum > traceframe_number
> + || (tfnum == traceframe_number && tfnum == 0)))
> found = 1;
> break;
> case tfind_tp:
> tp = get_tracepoint (num);
> - if (tp && tpnum == tp->number_on_target)
> + if (tp && tpnum == tp->number_on_target
> + /* Looks for the next trace frame if matched. */
> + && (tfnum > traceframe_number
> + || (tfnum == traceframe_number && tfnum == 0)))
> found = 1;
> break;
> case tfind_range:
> tfaddr = tfile_get_traceframe_address (tframe_offset);
> - if (addr1 <= tfaddr && tfaddr <= addr2)
> + if (addr1 <= tfaddr && tfaddr <= addr2
> + /* Looks for the next trace frame if matched. */
> + && (tfnum > traceframe_number
> + || (tfnum == traceframe_number && tfnum == 0)))
> found = 1;
> break;
> case tfind_outside:
> tfaddr = tfile_get_traceframe_address (tframe_offset);
> - if (!(addr1 <= tfaddr && tfaddr <= addr2))
> + if (!(addr1 <= tfaddr && tfaddr <= addr2)
> + /* Looks for the next trace frame if matched. */
> + && (tfnum > traceframe_number
> + || (tfnum == traceframe_number && tfnum == 0)))

I'm confused on why this bit of the predicate

(tfnum == traceframe_number && tfnum == 0)

is necessary. traceframe_number is -1 when not looking
at a traceframe yet, so "tfnum > traceframe_number"
should be sufficient, no?

I find it clearer to move the frame skipping a bit higher
up, even before the specific tfind tp/range/etc. matching.
Doing it this way also avoids unnecessary read/lseek system
calls done by tfile_get_traceframe_address.

WDYT?

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commit f837913c7a153a0e40a15f4a283deea201cbcbe7
Author: Pedro Alves <palves@redhat.com>
Date: Tue Feb 26 19:43:21 2013 +0000

Find the next matched trace file in 'tfile target'.

The previous patch exposes a bug in the tfile target when finding a
trace frame. Every time, GDB will scan tfile from the starting offset
and look for a matching trace frame starting from frame zero. But,
except when TYPE is tfind_number, GDB wants to find the *next* matched
trace frame after the current selected frame. So we need to check the
tfile trace frame number iterator is greater than the current trace
frame number (which means *next*), meaning skip all frames up to and
including the current.

Regression tested on x86_64 Fedora 17.

gdb/
2013-02-25 Yao Qi <yao@codesourcery.com>
Pedro Alves <palves@redhat.com>

* tracepoint.c (tfile_trace_find): For tfind
pc/tp/range/outside, look for the next trace frame instead of
always starting from frame 0.

diff --git a/gdb/tracepoint.c b/gdb/tracepoint.c
index ca104aa..9a80aa3 100644
--- a/gdb/tracepoint.c
+++ b/gdb/tracepoint.c
@@ -4316,35 +4316,46 @@ tfile_trace_find (enum trace_find_type type, int num,
((gdb_byte *) &data_size, 4,
gdbarch_byte_order (target_gdbarch ()));
offset += 4;
- switch (type)
+
+ if (type == tfind_number)
{
- case tfind_number:
+ /* Looking for a specific trace frame. */
if (tfnum == num)
found = 1;
- break;
- case tfind_pc:
- tfaddr = tfile_get_traceframe_address (tframe_offset);
- if (tfaddr == addr1)
- found = 1;
- break;
- case tfind_tp:
- tp = get_tracepoint (num);
- if (tp && tpnum == tp->number_on_target)
- found = 1;
- break;
- case tfind_range:
- tfaddr = tfile_get_traceframe_address (tframe_offset);
- if (addr1 <= tfaddr && tfaddr <= addr2)
- found = 1;
- break;
- case tfind_outside:
- tfaddr = tfile_get_traceframe_address (tframe_offset);
- if (!(addr1 <= tfaddr && tfaddr <= addr2))
- found = 1;
- break;
- default:
- internal_error (__FILE__, __LINE__, _("unknown tfind type"));
}
+ else
+ {
+ /* Start from the _next_ trace frame. */
+ if (tfnum > traceframe_number)
+ {
+ switch (type)
+ {
+ case tfind_pc:
+ tfaddr = tfile_get_traceframe_address (tframe_offset);
+ if (tfaddr == addr1)
+ found = 1;
+ break;
+ case tfind_tp:
+ tp = get_tracepoint (num);
+ if (tp && tpnum == tp->number_on_target)
+ found = 1;
+ break;
+ case tfind_range:
+ tfaddr = tfile_get_traceframe_address (tframe_offset);
+ if (addr1 <= tfaddr && tfaddr <= addr2)
+ found = 1;
+ break;
+ case tfind_outside:
+ tfaddr = tfile_get_traceframe_address (tframe_offset);
+ if (!(addr1 <= tfaddr && tfaddr <= addr2))
+ found = 1;
+ break;
+ default:
+ internal_error (__FILE__, __LINE__, _("unknown tfind type"));
+ }
+ }
+ }
+
if (found)
{
if (tpp)