Fix GDB internal error by using text (instead of data) section offset

Fedora Rawhide is now using gcc-12.0.  As part of updating to the
gcc-12.0 package set, Rawhide is also now using a version of libgcc_s
which lacks a .data section.  This causes gdb to fail in the following
fashion while debugging a program (such as gdb) which uses libgcc_s:

    (top-gdb) run
    Starting program: rawhide-master/bld/gdb/gdb
    ...
    objfiles.h:467: internal-error: sect_index_data not initialized
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    ...

I snipped the backtrace from the above output.  Instead, here's a
portion of a backtrace obtained using GDB's backtrace command.
(Obviously, in order to obtain it, I used a GDB which has been patched
with this commit.)

    #0  internal_error (
	file=0xc6a508 "gdb/objfiles.h", line=467,
	fmt=0xc6a4e8 "sect_index_data not initialized")
	at gdbsupport/errors.cc:51
    #1  0x00000000005f9651 in objfile::data_section_offset (this=0x4fa48f0)
	at gdb/objfiles.h:467
    #2  0x000000000097c5f8 in relocate_address (address=0x17244, objfile=0x4fa48f0)
	at gdb/stap-probe.c:1333
    #3  0x000000000097c630 in stap_probe::get_relocated_address (this=0xa1a17a0,
	objfile=0x4fa48f0)
	at gdb/stap-probe.c:1341
    #4  0x00000000004d7025 in create_exception_master_breakpoint_probe (
	objfile=0x4fa48f0)
	at gdb/breakpoint.c:3505
    #5  0x00000000004d7426 in create_exception_master_breakpoint ()
	at gdb/breakpoint.c:3575
    #6  0x00000000004efcc1 in breakpoint_re_set ()
	at gdb/breakpoint.c:13407
    #7  0x0000000000956998 in solib_add (pattern=0x0, from_tty=0, readsyms=1)
	at gdb/solib.c:1001
    #8  0x00000000009576a8 in handle_solib_event ()
	at gdb/solib.c:1269
    ...

The function 'relocate_address' in gdb/stap-probe.c attempts to do
its "relocation" by using objfile->data_section_offset().  That
method, data_section_offset() is defined as follows in objfiles.h:

  CORE_ADDR data_section_offset () const
  {
    return section_offsets[SECT_OFF_DATA (this)];
  }

The internal error occurs when the SECT_OFF_DATA macro finds that the
'sect_index_data' field is -1:

    #define SECT_OFF_DATA(objfile) \
	 ((objfile->sect_index_data == -1) \
	  ? (internal_error (__FILE__, __LINE__, \
			     _("sect_index_data not initialized")), -1)	\
	  : objfile->sect_index_data)

relocate_address() is obtaining the section offset in order to compute
a relocated address.  For some ABIs, such as the System V ABI, the
section offsets will all be the same.  So for those ABIs, it doesn't
matter which offset is used.  However, other ABIs, such as the FDPIC
ABI, will have different offsets for the various sections.  Thus, for
those ABIs, it is vital that this and other relocation code use the
correct offset.

In stap_probe::get_relocated_address, the address to which to add the
offset (thus forming the relocated address) is obtained via
this->get_address (); get_address is a getter for m_address in
probe.h.  It's documented/defined as follows (also in probe.h):

  /* The address where the probe is inserted, relative to
     SECT_OFF_TEXT.  */
  CORE_ADDR m_address;

(Thanks to Tom Tromey for this observation.)

So, based on this, the current use of data_section_offset /
SECT_OFF_DATA is wrong.  This relocation code should have been using
text_section_offset / SECT_OFF_TEXT all along.  That being the
case, I've adjusted the stap-probe.c relocation code accordingly.

Searching the sources turned up one other use of data_section_offset,
in gdb/dtrace-probe.c, so I've updated that code as well.  The same
reasoning presented above applies to this case too.

Summary:

	* gdb/dtrace-probe.c (dtrace_probe::get_relocated_address):
	Use method text_section_offset instead of data_section_offset.
	* gdb/stap-probe.c (relocate_address): Likewise.

diff --git a/gdb/dtrace-probe.c b/gdb/dtrace-probe.c
index ea4999ccebecb9cd00e216c92ed5b8b01907d9e9..9aeefb6060c4a51f880ec5c67ed747712f26e262 100644 (file)
--- a/gdb/dtrace-probe.c
+++ b/gdb/dtrace-probe.c
@@ -684,7 +684,7 @@ dtrace_probe::is_enabled () const
 CORE_ADDR
 dtrace_probe::get_relocated_address (struct objfile *objfile)
 {
-  return this->get_address () + objfile->data_section_offset ();
+  return this->get_address () + objfile->text_section_offset ();
 }
 
 /* Implementation of the get_argument_count method.  */

diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c
index 2310fdec86d203146d62c5995373deeff49b2e42..c4b24df756440ab9a36978a4dc4fe2b758bff684 100644 (file)
--- a/gdb/stap-probe.c
+++ b/gdb/stap-probe.c
@@ -1330,7 +1330,7 @@ stap_probe::parse_arguments (struct gdbarch *gdbarch)
 static CORE_ADDR
 relocate_address (CORE_ADDR address, struct objfile *objfile)
 {
-  return address + objfile->data_section_offset ();
+  return address + objfile->text_section_offset ();
 }
 
 /* Implementation of the get_relocated_address method.  */