[Bug objc/20503] New: ObjC runtime debugging support is severely broken

["gdb at crelg dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20503

            Bug ID: 20503
           Summary: ObjC runtime debugging support is severely broken
           Product: gdb
           Version: 7.11.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: objc
          Assignee: unassigned at sourceware dot org
          Reporter: gdb at crelg dot com
  Target Milestone: ---

Created attachment 9467
  --> https://sourceware.org/bugzilla/attachment.cgi?id=9467&action=edit
source + makefile

Component and OS

    Component  Version       OS
    ---------  ------------  -----------------------
    GDB        7.11.1        i686-w64-mingw32
    GDB        7.6.1-80.el7  x86_64-redhat-linux-gnu (*)

    (*) latest available through yum

Summary

    ObjC runtime debugging support is severely broken. Can't
    look up a class or invoke a method or pass a convenience
    variable -- even a plain C string.


Description

    1. Can't find classes. Objectve C classes are supposed to
       be global variables. They are not available from the
       GDB command line. That is like a C debugger that
       doesn't let you call any functions.

    2. Can't invoke methods. Trying [obj meth:arg] from the
       command line no longer works. It crashes GDB in some
       instances.

    3. These things used to work in older versions of GDB.


Steps to reproduce

    1. Compile and debug the attached program in GDB.

    2. Type the following commands in GDB.

    3. Show below each command are behaviors (a) expected and
       (b) obtained.


(gdb) b main
(gdb) r
(gdb) n 3

(gdb) p pr
# Print a variable
# This works
# $1 = (struct objc_object *) 0x403040 <_OBJC_MetaClass_Printer>
# $1 = (struct objc_object *) 0x6020e0 <_OBJC_MetaClass_Printer>

(gdb) po pr
# Use po (which calls _NSPrintForDebugger)
# This works
<Object: 0x403040>
<Object: 0x6020e0>

(gdb) p [pr prn:"foo"]
# Send a known message to a known receiver with a convenience variable
# Expected: "Value is 'foo'"
# Windows:  Can't find selector "prn:"
# Linux:    Program received signal SIGSEGV, Segmentation fault.
__objc_responds_to (sel=<optimized out>, object=0x6020e0
<_OBJC_MetaClass_Printer>) at
/usr/src/debug/gcc-4.8.5-20150702/libobjc/sendmsg.c:397
397       res = sarray_get_safe (dtable, (size_t) sel->sel_id);

(gdb) p [Printer prn:"foo"]
# Send a known message to a known receiver with a convenience variable
# Expected: "Value is 'foo'"
# Windows:  No symbol "Printer" in current context. 
# Linux:    Program received signal SIGSEGV, Segmentation fault.
__objc_responds_to (sel=<optimized out>, object=0x602160 <_OBJC_Class_Printer>)
at /usr/src/debug/gcc-4.8.5-20150702/libobjc/sendmsg.c:397
397       res = sarray_get_safe (dtable, (size_t) sel->sel_id);

(gdb) p [Printer evaporate]
# Invoke an unknown method
# Expected: Object (id) 0x403040 <Printer> does not respond to selector
"evaporate"
# Windows:  Can't find selector "evaporate" (or any valid selector for that
matter)
# Linux:    Program received signal SIGSEGV, Segmentation fault.
__objc_responds_to (sel=<optimized out>, object=0x602160 <_OBJC_Class_Printer>)
at /usr/src/debug/gcc-4.8.5-20150702/libobjc/sendmsg.c:397
397       res = sarray_get_safe (dtable, (size_t) sel->sel_id);

(gdb) p Printer
# Print an Objective C class (a global variable)
# Expected: $1 = (struct objc_object *) 0x403040 <_OBJC_MetaClass_Printer>
# Windows:  No symbol "Printer" in current context.
# Linux:    A syntax error in expression, near `Printer'.

(gdb) p [Printer class]
# Invoke a method on an object (an Objective C class which should be a global
variable)
# Expected: $1 = (struct objc_object *) 0x403040 <_OBJC_MetaClass_Printer>
# Windows:  No symbol "Printer" in current context.
# Linux:    Program received signal SIGSEGV, Segmentation fault.
__objc_responds_to (sel=<optimized out>, object=0x602160 <_OBJC_Class_Printer>)
at /usr/src/debug/gcc-4.8.5-20150702/libobjc/sendmsg.c:397
397       res = sarray_get_safe (dtable, (size_t) sel->sel_id);

(gdb) p getClass("Printer")
# Call a function with a convenience variable
# Expected: $1 = (struct objc_object *) 0x403040 <_OBJC_MetaClass_Printer>
# Win+Lin:  $1 = (struct objc_object *) 0x0

(gdb) p "foo"
# Create a convenience variable
# Expected: $1 = (char *) "foo"
# Win+Lin:  $1 = <error reading variable>

(gdb) p objc_getClass("Printer")
# Call a function with a convenience variable
# Expected: $1 = (struct objc_object *) 0x403040 <_OBJC_MetaClass_Printer>
# Windows:  Program received signal SIGSEGV, Segmentation fault. 0x00000000 in
?? ()
# Linux:    $1 = (struct objc_class *) 0x0

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