[COMMITTED PATCH][PR gdb/25939] Move push_target call earlier in procfs.c

Rainer Orth
2020-06-21T16:37:24Z

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Hi Pedro,

> On 6/19/20 1:36 PM, Rainer Orth wrote:
>>> On 6/18/20 3:55 PM, Pedro Alves via Gdb-patches wrote:
>
>>> Your push_target fix is still necessary, FAOD.
>>
>> Should I push it as is (with an appropriate description, of course) or
>> would the code change need a comment, too?
>
> It's fine without a comment. I think you can remove the
> push_target call from procfs_init_inferior at the same time,
> too, as that one becomes unnecessary. Basically make the fix be
> about moving the push_target call earlier.

that works just fine. Here's what I've committed after testing both
pathes together on amd64-pc-solaris2.11.

Rainer

--
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

[PR gdb/25939] Move push_target call earlier in procfs.c

Since the multi-target patch, the run command fails on Solaris with an
assertion failure even for a trivial program:

$ ./gdb -D ./data-directory ./hello
GNU gdb (GDB) 10.0.50.20200106-git
[...]
Reading symbols from ./hello...
(gdb) run
Starting program: /vol/obj/gnu/gdb/gdb/reghunt/no-resync/122448/gdb/hello
/vol/src/gnu/gdb/hg/master/reghunt/gdb/thread.c:336: internal-error:
thread_info::thread_info(inferior*, ptid_t): Assertion `inf_ != NULL'
failed.

Here's the start of the corresponding stack trace:

#0 internal_error (
file=file@entry=0x966150
"/vol/src/gnu/gdb/hg/master/reghunt/gdb/thread.c", line=line@entry=336,
fmt=0x9ddb94 "%s: Assertion `%s' failed.")
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/gdbsupport/errors.c:51
#1 0x0000000000ef81f4 in thread_info::thread_info (this=0x1212020,
inf_=<optimized out>, ptid_=...)
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/thread.c:344
#2 0x0000000000ef82cd in new_thread (inf=inf@entry=0x0, ptid=...)
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/thread.c:239
#3 0x0000000000efac3c in add_thread_silent (
targ=targ@entry=0x11b0940 <the_procfs_target>, ptid=...)
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/thread.c:304
#4 0x0000000000d90692 in procfs_target::create_inferior (
this=0x11b0940 <the_procfs_target>,
exec_file=0x13dbef0
"/vol/obj/gnu/gdb/gdb/reghunt/no-resync/122448/gdb/hello", allargs="",
env=0x13c48f0, from_tty=<optimized out>)
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/gdbsupport/ptid.h:47
#5 0x0000000000c84e64 in run_command_1 (args=<optimized out>, from_tty=1,
run_how=run_how@entry=RUN_NORMAL)
at /vol/gcc-9/include/c++/9.1.0/bits/basic_string.h:263
#6 0x0000000000c85007 in run_command (args=<optimized out>,
from_tty=<optimized out>)
at /vol/src/gnu/gdb/hg/master/reghunt/gdb/infcmd.c:687

Looking closer, I found that in add_thread_silent as called from
procfs.c (procfs_target::create_inferior) find_inferior_ptid returns
NULL. The all_inferiors (targ) iterator comes up empty.

Going from there, I see that in add_thread_silent

m_target_stack = {m_top = file_stratum, m_stack = {0x20190e0
<the_dummy_target>, 0x200b8c0 <exec_ops>, 0x0, 0x0, 0x0, 0x0, 0x0}}}

i.e. the_procfs_target is missing compared to the_amd64_linux_nat_target
on Linux/x86_64.

Moving the push_target call earlier allows debugging to get over the
initial assertion failure. I run instead into

procfs: couldn't find pid 0 in procinfo list.

which is fixed by

https://sourceware.org/pipermail/gdb-patches/2020-June/169674.html

Both patches tested together on amd64-pc-solaris2.11.

PR gdb/25939
* procfs.c (procfs_target::procfs_init_inferior): Move push_target
call ...
(procfs_target::create_inferior): ... here.

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# HG changeset patch
# Parent 34403039561e7d3e10eb37561e6b574370a182d5
Move push_target call earlier in procfs.c [PR25939]

diff --git a/gdb/procfs.c b/gdb/procfs.c
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -2781,11 +2781,6 @@ procfs_target::procfs_init_inferior (int
int fail;
int lwpid;

- /* This routine called on the parent side (GDB side)
- after GDB forks the inferior. */
- if (!target_is_pushed (this))
- push_target (this);
-
pi = create_procinfo (pid, 0);
if (pi == NULL)
perror (_("procfs: out of memory in 'init_inferior'"));
@@ -3006,6 +3001,9 @@ procfs_target::create_inferior (const ch
shell_file = tryname;
}

+ if (!target_is_pushed (this))
+ push_target (this);
+
pid = fork_inferior (exec_file, allargs, env, procfs_set_exec_trap,
NULL, NULL, shell_file, NULL);