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<!--{
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"Title": "Debugging Go Code with GDB",
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"Path": "/doc/gdb"
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}-->
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<!--
|
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NOTE: In this document and others in this directory, the convention is to
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|
set fixed-width phrases with non-fixed-width spaces, as in
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<code>hello</code> <code>world</code>.
|
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|
Do not send CLs removing the interior tags from such phrases.
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-->
|
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<i>
|
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|
<p>
|
|
|
The following instructions apply to the standard toolchain
|
|
|
(the <code>gc</code> Go compiler and tools).
|
|
|
Gccgo has native gdb support.
|
|
|
</p>
|
|
|
<p>
|
|
|
Note that
|
|
|
<a href="https://github.com/go-delve/delve">Delve</a> is a better
|
|
|
alternative to GDB when debugging Go programs built with the standard
|
|
|
toolchain. It understands the Go runtime, data structures, and
|
|
|
expressions better than GDB. Delve currently supports Linux, OSX,
|
|
|
and Windows on <code>amd64</code>.
|
|
|
For the most up-to-date list of supported platforms, please see
|
|
|
<a href="https://github.com/go-delve/delve/tree/master/Documentation/installation">
|
|
|
the Delve documentation</a>.
|
|
|
</p>
|
|
|
</i>
|
|
|
|
|
|
<p>
|
|
|
GDB does not understand Go programs well.
|
|
|
The stack management, threading, and runtime contain aspects that differ
|
|
|
enough from the execution model GDB expects that they can confuse
|
|
|
the debugger and cause incorrect results even when the program is
|
|
|
compiled with gccgo.
|
|
|
As a consequence, although GDB can be useful in some situations (e.g.,
|
|
|
debugging Cgo code, or debugging the runtime itself), it is not
|
|
|
a reliable debugger for Go programs, particularly heavily concurrent
|
|
|
ones. Moreover, it is not a priority for the Go project to address
|
|
|
these issues, which are difficult.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
In short, the instructions below should be taken only as a guide to how
|
|
|
to use GDB when it works, not as a guarantee of success.
|
|
|
|
|
|
Besides this overview you might want to consult the
|
|
|
<a href="https://sourceware.org/gdb/current/onlinedocs/gdb/">GDB manual</a>.
|
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|
</p>
|
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|
|
|
|
<p>
|
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|
</p>
|
|
|
|
|
|
<h2 id="Introduction">Introduction</h2>
|
|
|
|
|
|
<p>
|
|
|
When you compile and link your Go programs with the <code>gc</code> toolchain
|
|
|
on Linux, macOS, FreeBSD or NetBSD, the resulting binaries contain DWARFv4
|
|
|
debugging information that recent versions (≥7.5) of the GDB debugger can
|
|
|
use to inspect a live process or a core dump.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
Pass the <code>'-w'</code> flag to the linker to omit the debug information
|
|
|
(for example, <code>go</code> <code>build</code> <code>-ldflags=-w</code> <code>prog.go</code>).
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
The code generated by the <code>gc</code> compiler includes inlining of
|
|
|
function invocations and registerization of variables. These optimizations
|
|
|
can sometimes make debugging with <code>gdb</code> harder.
|
|
|
If you find that you need to disable these optimizations,
|
|
|
build your program using <code>go</code> <code>build</code> <code>-gcflags=all="-N -l"</code>.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
If you want to use gdb to inspect a core dump, you can trigger a dump
|
|
|
on a program crash, on systems that permit it, by setting
|
|
|
<code>GOTRACEBACK=crash</code> in the environment (see the
|
|
|
<a href="/pkg/runtime/#hdr-Environment_Variables"> runtime package
|
|
|
documentation</a> for more info).
|
|
|
</p>
|
|
|
|
|
|
<h3 id="Common_Operations">Common Operations</h3>
|
|
|
|
|
|
<ul>
|
|
|
<li>
|
|
|
Show file and line number for code, set breakpoints and disassemble:
|
|
|
<pre>(gdb) <b>list</b>
|
|
|
(gdb) <b>list <i>line</i></b>
|
|
|
(gdb) <b>list <i>file.go</i>:<i>line</i></b>
|
|
|
(gdb) <b>break <i>line</i></b>
|
|
|
(gdb) <b>break <i>file.go</i>:<i>line</i></b>
|
|
|
(gdb) <b>disas</b></pre>
|
|
|
</li>
|
|
|
<li>
|
|
|
Show backtraces and unwind stack frames:
|
|
|
<pre>(gdb) <b>bt</b>
|
|
|
(gdb) <b>frame <i>n</i></b></pre>
|
|
|
</li>
|
|
|
<li>
|
|
|
Show the name, type and location on the stack frame of local variables,
|
|
|
arguments and return values:
|
|
|
<pre>(gdb) <b>info locals</b>
|
|
|
(gdb) <b>info args</b>
|
|
|
(gdb) <b>p variable</b>
|
|
|
(gdb) <b>whatis variable</b></pre>
|
|
|
</li>
|
|
|
<li>
|
|
|
Show the name, type and location of global variables:
|
|
|
<pre>(gdb) <b>info variables <i>regexp</i></b></pre>
|
|
|
</li>
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
<h3 id="Go_Extensions">Go Extensions</h3>
|
|
|
|
|
|
<p>
|
|
|
A recent extension mechanism to GDB allows it to load extension scripts for a
|
|
|
given binary. The toolchain uses this to extend GDB with a handful of
|
|
|
commands to inspect internals of the runtime code (such as goroutines) and to
|
|
|
pretty print the built-in map, slice and channel types.
|
|
|
</p>
|
|
|
|
|
|
<ul>
|
|
|
<li>
|
|
|
Pretty printing a string, slice, map, channel or interface:
|
|
|
<pre>(gdb) <b>p <i>var</i></b></pre>
|
|
|
</li>
|
|
|
<li>
|
|
|
A $len() and $cap() function for strings, slices and maps:
|
|
|
<pre>(gdb) <b>p $len(<i>var</i>)</b></pre>
|
|
|
</li>
|
|
|
<li>
|
|
|
A function to cast interfaces to their dynamic types:
|
|
|
<pre>(gdb) <b>p $dtype(<i>var</i>)</b>
|
|
|
(gdb) <b>iface <i>var</i></b></pre>
|
|
|
<p class="detail"><b>Known issue:</b> GDB can’t automatically find the dynamic
|
|
|
type of an interface value if its long name differs from its short name
|
|
|
(annoying when printing stacktraces, the pretty printer falls back to printing
|
|
|
the short type name and a pointer).</p>
|
|
|
</li>
|
|
|
<li>
|
|
|
Inspecting goroutines:
|
|
|
<pre>(gdb) <b>info goroutines</b>
|
|
|
(gdb) <b>goroutine <i>n</i> <i>cmd</i></b>
|
|
|
(gdb) <b>help goroutine</b></pre>
|
|
|
For example:
|
|
|
<pre>(gdb) <b>goroutine 12 bt</b></pre>
|
|
|
You can inspect all goroutines by passing <code>all</code> instead of a specific goroutine's ID.
|
|
|
For example:
|
|
|
<pre>(gdb) <b>goroutine all bt</b></pre>
|
|
|
</li>
|
|
|
</ul>
|
|
|
|
|
|
<p>
|
|
|
If you'd like to see how this works, or want to extend it, take a look at <a
|
|
|
href="/src/runtime/runtime-gdb.py">src/runtime/runtime-gdb.py</a> in
|
|
|
the Go source distribution. It depends on some special magic types
|
|
|
(<code>hash<T,U></code>) and variables (<code>runtime.m</code> and
|
|
|
<code>runtime.g</code>) that the linker
|
|
|
(<a href="/src/cmd/link/internal/ld/dwarf.go">src/cmd/link/internal/ld/dwarf.go</a>) ensures are described in
|
|
|
the DWARF code.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
If you're interested in what the debugging information looks like, run
|
|
|
<code>objdump</code> <code>-W</code> <code>a.out</code> and browse through the <code>.debug_*</code>
|
|
|
sections.
|
|
|
</p>
|
|
|
|
|
|
|
|
|
<h3 id="Known_Issues">Known Issues</h3>
|
|
|
|
|
|
<ol>
|
|
|
<li>String pretty printing only triggers for type string, not for types derived
|
|
|
from it.</li>
|
|
|
<li>Type information is missing for the C parts of the runtime library.</li>
|
|
|
<li>GDB does not understand Go’s name qualifications and treats
|
|
|
<code>"fmt.Print"</code> as an unstructured literal with a <code>"."</code>
|
|
|
that needs to be quoted. It objects even more strongly to method names of
|
|
|
the form <code>pkg.(*MyType).Meth</code>.
|
|
|
<li>As of Go 1.11, debug information is compressed by default.
|
|
|
Older versions of gdb, such as the one available by default on MacOS,
|
|
|
do not understand the compression.
|
|
|
You can generate uncompressed debug information by using <code>go
|
|
|
build -ldflags=-compressdwarf=false</code>.
|
|
|
(For convenience you can put the <code>-ldflags</code> option in
|
|
|
the <a href="/cmd/go/#hdr-Environment_variables"><code>GOFLAGS</code>
|
|
|
environment variable</a> so that you don't have to specify it each time.)
|
|
|
</li>
|
|
|
</ol>
|
|
|
|
|
|
<h2 id="Tutorial">Tutorial</h2>
|
|
|
|
|
|
<p>
|
|
|
In this tutorial we will inspect the binary of the
|
|
|
<a href="/pkg/regexp/">regexp</a> package's unit tests. To build the binary,
|
|
|
change to <code>$GOROOT/src/regexp</code> and run <code>go</code> <code>test</code> <code>-c</code>.
|
|
|
This should produce an executable file named <code>regexp.test</code>.
|
|
|
</p>
|
|
|
|
|
|
|
|
|
<h3 id="Getting_Started">Getting Started</h3>
|
|
|
|
|
|
<p>
|
|
|
Launch GDB, debugging <code>regexp.test</code>:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
$ <b>gdb regexp.test</b>
|
|
|
GNU gdb (GDB) 7.2-gg8
|
|
|
Copyright (C) 2010 Free Software Foundation, Inc.
|
|
|
License GPLv 3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
|
|
|
Type "show copying" and "show warranty" for licensing/warranty details.
|
|
|
This GDB was configured as "x86_64-linux".
|
|
|
|
|
|
Reading symbols from /home/user/go/src/regexp/regexp.test...
|
|
|
done.
|
|
|
Loading Go Runtime support.
|
|
|
(gdb)
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
The message "Loading Go Runtime support" means that GDB loaded the
|
|
|
extension from <code>$GOROOT/src/runtime/runtime-gdb.py</code>.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
To help GDB find the Go runtime sources and the accompanying support script,
|
|
|
pass your <code>$GOROOT</code> with the <code>'-d'</code> flag:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
$ <b>gdb regexp.test -d $GOROOT</b>
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
If for some reason GDB still can't find that directory or that script, you can load
|
|
|
it by hand by telling gdb (assuming you have the go sources in
|
|
|
<code>~/go/</code>):
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>source ~/go/src/runtime/runtime-gdb.py</b>
|
|
|
Loading Go Runtime support.
|
|
|
</pre>
|
|
|
|
|
|
<h3 id="Inspecting_the_source">Inspecting the source</h3>
|
|
|
|
|
|
<p>
|
|
|
Use the <code>"l"</code> or <code>"list"</code> command to inspect source code.
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>l</b>
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
List a specific part of the source parameterizing <code>"list"</code> with a
|
|
|
function name (it must be qualified with its package name).
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>l main.main</b>
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
List a specific file and line number:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>l regexp.go:1</b>
|
|
|
(gdb) <i># Hit enter to repeat last command. Here, this lists next 10 lines.</i>
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
<h3 id="Naming">Naming</h3>
|
|
|
|
|
|
<p>
|
|
|
Variable and function names must be qualified with the name of the packages
|
|
|
they belong to. The <code>Compile</code> function from the <code>regexp</code>
|
|
|
package is known to GDB as <code>'regexp.Compile'</code>.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
Methods must be qualified with the name of their receiver types. For example,
|
|
|
the <code>*Regexp</code> type’s <code>String</code> method is known as
|
|
|
<code>'regexp.(*Regexp).String'</code>.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
Variables that shadow other variables are magically suffixed with a number in the debug info.
|
|
|
Variables referenced by closures will appear as pointers magically prefixed with '&'.
|
|
|
</p>
|
|
|
|
|
|
<h3 id="Setting_breakpoints">Setting breakpoints</h3>
|
|
|
|
|
|
<p>
|
|
|
Set a breakpoint at the <code>TestFind</code> function:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>b 'regexp.TestFind'</b>
|
|
|
Breakpoint 1 at 0x424908: file /home/user/go/src/regexp/find_test.go, line 148.
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Run the program:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>run</b>
|
|
|
Starting program: /home/user/go/src/regexp/regexp.test
|
|
|
|
|
|
Breakpoint 1, regexp.TestFind (t=0xf8404a89c0) at /home/user/go/src/regexp/find_test.go:148
|
|
|
148 func TestFind(t *testing.T) {
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Execution has paused at the breakpoint.
|
|
|
See which goroutines are running, and what they're doing:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>info goroutines</b>
|
|
|
1 waiting runtime.gosched
|
|
|
* 13 running runtime.goexit
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
the one marked with the <code>*</code> is the current goroutine.
|
|
|
</p>
|
|
|
|
|
|
<h3 id="Inspecting_the_stack">Inspecting the stack</h3>
|
|
|
|
|
|
<p>
|
|
|
Look at the stack trace for where we’ve paused the program:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>bt</b> <i># backtrace</i>
|
|
|
#0 regexp.TestFind (t=0xf8404a89c0) at /home/user/go/src/regexp/find_test.go:148
|
|
|
#1 0x000000000042f60b in testing.tRunner (t=0xf8404a89c0, test=0x573720) at /home/user/go/src/testing/testing.go:156
|
|
|
#2 0x000000000040df64 in runtime.initdone () at /home/user/go/src/runtime/proc.c:242
|
|
|
#3 0x000000f8404a89c0 in ?? ()
|
|
|
#4 0x0000000000573720 in ?? ()
|
|
|
#5 0x0000000000000000 in ?? ()
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
The other goroutine, number 1, is stuck in <code>runtime.gosched</code>, blocked on a channel receive:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>goroutine 1 bt</b>
|
|
|
#0 0x000000000040facb in runtime.gosched () at /home/user/go/src/runtime/proc.c:873
|
|
|
#1 0x00000000004031c9 in runtime.chanrecv (c=void, ep=void, selected=void, received=void)
|
|
|
at /home/user/go/src/runtime/chan.c:342
|
|
|
#2 0x0000000000403299 in runtime.chanrecv1 (t=void, c=void) at/home/user/go/src/runtime/chan.c:423
|
|
|
#3 0x000000000043075b in testing.RunTests (matchString={void (struct string, struct string, bool *, error *)}
|
|
|
0x7ffff7f9ef60, tests= []testing.InternalTest = {...}) at /home/user/go/src/testing/testing.go:201
|
|
|
#4 0x00000000004302b1 in testing.Main (matchString={void (struct string, struct string, bool *, error *)}
|
|
|
0x7ffff7f9ef80, tests= []testing.InternalTest = {...}, benchmarks= []testing.InternalBenchmark = {...})
|
|
|
at /home/user/go/src/testing/testing.go:168
|
|
|
#5 0x0000000000400dc1 in main.main () at /home/user/go/src/regexp/_testmain.go:98
|
|
|
#6 0x00000000004022e7 in runtime.mainstart () at /home/user/go/src/runtime/amd64/asm.s:78
|
|
|
#7 0x000000000040ea6f in runtime.initdone () at /home/user/go/src/runtime/proc.c:243
|
|
|
#8 0x0000000000000000 in ?? ()
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
The stack frame shows we’re currently executing the <code>regexp.TestFind</code> function, as expected.
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>info frame</b>
|
|
|
Stack level 0, frame at 0x7ffff7f9ff88:
|
|
|
rip = 0x425530 in regexp.TestFind (/home/user/go/src/regexp/find_test.go:148);
|
|
|
saved rip 0x430233
|
|
|
called by frame at 0x7ffff7f9ffa8
|
|
|
source language minimal.
|
|
|
Arglist at 0x7ffff7f9ff78, args: t=0xf840688b60
|
|
|
Locals at 0x7ffff7f9ff78, Previous frame's sp is 0x7ffff7f9ff88
|
|
|
Saved registers:
|
|
|
rip at 0x7ffff7f9ff80
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
The command <code>info</code> <code>locals</code> lists all variables local to the function and their values, but is a bit
|
|
|
dangerous to use, since it will also try to print uninitialized variables. Uninitialized slices may cause gdb to try
|
|
|
to print arbitrary large arrays.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
The function’s arguments:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>info args</b>
|
|
|
t = 0xf840688b60
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
When printing the argument, notice that it’s a pointer to a
|
|
|
<code>Regexp</code> value. Note that GDB has incorrectly put the <code>*</code>
|
|
|
on the right-hand side of the type name and made up a 'struct' keyword, in traditional C style.
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>p re</b>
|
|
|
(gdb) p t
|
|
|
$1 = (struct testing.T *) 0xf840688b60
|
|
|
(gdb) p t
|
|
|
$1 = (struct testing.T *) 0xf840688b60
|
|
|
(gdb) p *t
|
|
|
$2 = {errors = "", failed = false, ch = 0xf8406f5690}
|
|
|
(gdb) p *t->ch
|
|
|
$3 = struct hchan<*testing.T>
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
That <code>struct</code> <code>hchan<*testing.T></code> is the
|
|
|
runtime-internal representation of a channel. It is currently empty,
|
|
|
or gdb would have pretty-printed its contents.
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
Stepping forward:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>n</b> <i># execute next line</i>
|
|
|
149 for _, test := range findTests {
|
|
|
(gdb) <i># enter is repeat</i>
|
|
|
150 re := MustCompile(test.pat)
|
|
|
(gdb) <b>p test.pat</b>
|
|
|
$4 = ""
|
|
|
(gdb) <b>p re</b>
|
|
|
$5 = (struct regexp.Regexp *) 0xf84068d070
|
|
|
(gdb) <b>p *re</b>
|
|
|
$6 = {expr = "", prog = 0xf840688b80, prefix = "", prefixBytes = []uint8, prefixComplete = true,
|
|
|
prefixRune = 0, cond = 0 '\000', numSubexp = 0, longest = false, mu = {state = 0, sema = 0},
|
|
|
machine = []*regexp.machine}
|
|
|
(gdb) <b>p *re->prog</b>
|
|
|
$7 = {Inst = []regexp/syntax.Inst = {{Op = 5 '\005', Out = 0, Arg = 0, Rune = []int}, {Op =
|
|
|
6 '\006', Out = 2, Arg = 0, Rune = []int}, {Op = 4 '\004', Out = 0, Arg = 0, Rune = []int}},
|
|
|
Start = 1, NumCap = 2}
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
<p>
|
|
|
We can step into the <code>String</code>function call with <code>"s"</code>:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>s</b>
|
|
|
regexp.(*Regexp).String (re=0xf84068d070, noname=void) at /home/user/go/src/regexp/regexp.go:97
|
|
|
97 func (re *Regexp) String() string {
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Get a stack trace to see where we are:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>bt</b>
|
|
|
#0 regexp.(*Regexp).String (re=0xf84068d070, noname=void)
|
|
|
at /home/user/go/src/regexp/regexp.go:97
|
|
|
#1 0x0000000000425615 in regexp.TestFind (t=0xf840688b60)
|
|
|
at /home/user/go/src/regexp/find_test.go:151
|
|
|
#2 0x0000000000430233 in testing.tRunner (t=0xf840688b60, test=0x5747b8)
|
|
|
at /home/user/go/src/testing/testing.go:156
|
|
|
#3 0x000000000040ea6f in runtime.initdone () at /home/user/go/src/runtime/proc.c:243
|
|
|
....
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Look at the source code:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>l</b>
|
|
|
92 mu sync.Mutex
|
|
|
93 machine []*machine
|
|
|
94 }
|
|
|
95
|
|
|
96 // String returns the source text used to compile the regular expression.
|
|
|
97 func (re *Regexp) String() string {
|
|
|
98 return re.expr
|
|
|
99 }
|
|
|
100
|
|
|
101 // Compile parses a regular expression and returns, if successful,
|
|
|
</pre>
|
|
|
|
|
|
<h3 id="Pretty_Printing">Pretty Printing</h3>
|
|
|
|
|
|
<p>
|
|
|
GDB's pretty printing mechanism is triggered by regexp matches on type names. An example for slices:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>p utf</b>
|
|
|
$22 = []uint8 = {0 '\000', 0 '\000', 0 '\000', 0 '\000'}
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Since slices, arrays and strings are not C pointers, GDB can't interpret the subscripting operation for you, but
|
|
|
you can look inside the runtime representation to do that (tab completion helps here):
|
|
|
</p>
|
|
|
<pre>
|
|
|
|
|
|
(gdb) <b>p slc</b>
|
|
|
$11 = []int = {0, 0}
|
|
|
(gdb) <b>p slc-></b><i><TAB></i>
|
|
|
array slc len
|
|
|
(gdb) <b>p slc->array</b>
|
|
|
$12 = (int *) 0xf84057af00
|
|
|
(gdb) <b>p slc->array[1]</b>
|
|
|
$13 = 0</pre>
|
|
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
The extension functions $len and $cap work on strings, arrays and slices:
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>p $len(utf)</b>
|
|
|
$23 = 4
|
|
|
(gdb) <b>p $cap(utf)</b>
|
|
|
$24 = 4
|
|
|
</pre>
|
|
|
|
|
|
<p>
|
|
|
Channels and maps are 'reference' types, which gdb shows as pointers to C++-like types <code>hash<int,string>*</code>. Dereferencing will trigger prettyprinting
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
Interfaces are represented in the runtime as a pointer to a type descriptor and a pointer to a value. The Go GDB runtime extension decodes this and automatically triggers pretty printing for the runtime type. The extension function <code>$dtype</code> decodes the dynamic type for you (examples are taken from a breakpoint at <code>regexp.go</code> line 293.)
|
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
|
(gdb) <b>p i</b>
|
|
|
$4 = {str = "cbb"}
|
|
|
(gdb) <b>whatis i</b>
|
|
|
type = regexp.input
|
|
|
(gdb) <b>p $dtype(i)</b>
|
|
|
$26 = (struct regexp.inputBytes *) 0xf8400b4930
|
|
|
(gdb) <b>iface i</b>
|
|
|
regexp.input: struct regexp.inputBytes *
|
|
|
</pre>
|
