Re: SOLVELD [cross] building gdb for the 64bit Hurd?

[janneke]

Samuel Thibault writes:

Hi!

> janneke@gnu.org, le ven. 15 nov. 2024 11:14:39 +0100, a ecrit:
>> As a corollary, using this GDB I found that the statically built tar
>> segfaults on the vtrying to issue the
>> 
>>    tar: Option --mtime: Treating date '@1' as 1970-01-01 01:00:01
>> 
>> warning:
>> 
>>          WARN ((0, 0, _("Option %s: Treating date '%s' as %s"),
>>                 p->option, p->date, treated_as));
>> 
>> as it looks like, on the
>> 274      vfprintf (stderr, message, args);
>> 
>> call.  I guess I'll try replacing that with a simple fprintf for the
>> 64bit Hurd,
>
> That's however very worth investigating because something fishy is
> at hand here, and better fix it here where it should be easy to
> investigate, rather than in other places where it'd be way more tricky.

> For a start, are p->option, p->date, and treated_as actually valid
> strings?

Yes

(gdb) p *p
$4 = {next = 0x0, ts = {tv_sec = 1, tv_nsec = 0}, rpl_option = 0x5b0132 
"--mtime", date = 0x2000000033e0 "@1"}

Everything looks fine.  I'm using the attached patch to work around this
and tested printing errors and warnings; everything works.

This looks like a pretty simple place, but gnulib error reporting functions
are a bit tricky:

--8<---------------cut here---------------start------------->8---
Thread 4 hit Breakpoint 5, __error (status=0, errnum=0, message=0x5aff78 
"Option %s: Treating date '%s' as %s") at error.c:274
274         vfprintf (stderr, message, args);
(gdb) p stderr
$6 = (FILE *) 0x608400 <_IO_2_1_stderr_>
(gdb) p message
$7 = 0x5aff78 "Option %s: Treating date '%s' as %s"
(gdb) p args
No symbol "args" in current context.
(gdb) down
Bottom (innermost) frame selected; you cannot go down.
(gdb) up
#1  0x000000000042897b in report_textual_dates (args=0x160fb40) at tar.c:1113
1113                WARN ((0, 0, _("Option %s: Treating date '%s' as %s"),
(gdb) s
__error_internal (status=0, errnum=0, message=0x5aff78 "Option %s: Treating 
date '%s' as %s", args=args@entry=0x160f9f8, mode_flags=mode_flags@entry=0) at 
error.c:242
242               res = mbsrtowcs (wmessage, &tmp, len, &st);
(gdb) s
243               if (res != len)
(gdb) s
Thread 4 received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00000000004f532d in __error_internal (status=0, errnum=0, 
message=0x5aff78 "Option %s: Treating date '%s' as %s", 
args=args@entry=0x160f9f8, mode_flags=mode_flags@entry=0) at error.c:243
#2  0x00000000004f5425 in __error (status=<optimized out>, errnum=<optimized 
out>, message=<optimized out>) at error.c:274
#3  0x000000000042897b in report_textual_dates (args=0x160fb40) at tar.c:1113
#4  0x000000000042c418 in decode_options (argc=10, argv=0x200000001270) at 
tar.c:2730
#5  0x000000000042c548 in main (argc=8, argv=0x160fcb8) at tar.c:2797
(gdb) up
#1  0x00000000004f532d in __error_internal (status=0, errnum=0, 
message=0x5aff78 "Option %s: Treating date '%s' as %s", 
args=args@entry=0x160f9f8, mode_flags=mode_flags@entry=0) at error.c:243
243               if (res != len)
(gdb) up
#2  0x00000000004f5425 in __error (status=<optimized out>, errnum=<optimized 
out>, message=<optimized out>) at error.c:274
274         vfprintf (stderr, message, args);
--8<---------------cut here---------------end--------------->8---

I don't understand how single-stepping on vfprintf (lne 274) brings me
to line 234, which is inside "#if _LIBC" code.

Greetings,
Janneke

--- ./tar-1.34/lib/paxlib.h.orig        2024-11-15 11:47:57.340427845 +0100
+++ ./tar-1.34/lib/paxlib.h     2024-11-15 12:13:30.554724056 +0100
@@ -42,6 +42,17 @@
    single argument of the form ((0, errno, _("FORMAT"), Args...)).  errno
    is zero when the error is not being detected by the system.  */
 
+#if __GNU__ && __x86_64__
+
+#define PRINT_WARN(x, y, ...) fprintf (stderr, __VA_ARGS__)
+#define WARN(Args) do { PRINT_WARN Args; } while (0)
+
+#define ERROR(Args) do { PRINT_WARN Args , exit (PAXEXIT_FAILURE); } while (0)
+#define FATAL_ERROR(Args) do { PRINT_WARN Args , fatal_exit (); } while (0)
+#define USAGE_ERROR(Args) do { PRINT_WARN Args , usage (PAXEXIT_FAILURE); } 
while (0)
+
+#else
+
 #define WARN(Args) \
   do { if (error_hook) error_hook (); error Args; } while (0)
 #define ERROR(Args) \
@@ -69,6 +80,8 @@
     }                                          \
   while (0)
 
+#endif
+
 extern int exit_status;
 
 void pax_decode_mode (mode_t mode, char *string);

-- 
Janneke Nieuwenhuizen <janneke@gnu.org>  | GNU LilyPond https://LilyPond.org
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