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[patch] solib-svr4.c: Document why we need section info of the dynamic linker.
- From: dje at google dot com (Doug Evans)
- To: gdb-patches at sourceware dot org
- Date: Tue, 26 Jan 2010 12:41:19 -0800 (PST)
- Subject: [patch] solib-svr4.c: Document why we need section info of the dynamic linker.
Hi.
This patch is based on info from Daniel on irc.
It documents why we don't call create_solib_event_breakpoint (sym_addr)
unless we have section info on the dynamic linker.
I'll check it in tomorrow if there are no objections.
For the ARM case, one *could* try to pass a non-addr_bits_remove'd
address to create_solib_event_breakpoint and get that working.
Another hacky thought is to fake the necessary section/symbol info
when gdb can't find the dynamic linker (which can happen for cross-debugging
via gdbserver).
That is left for a later pass. This patch just documents what's there today.
2010-01-26 Doug Evans <dje@google.com>
* solib-svr4.c (enable_break): Document why we need section info
of the dynamic linker.
Index: solib-svr4.c
===================================================================
RCS file: /cvs/src/src/gdb/solib-svr4.c,v
retrieving revision 1.115
diff -u -p -r1.115 solib-svr4.c
--- solib-svr4.c 14 Jan 2010 21:16:52 -0000 1.115
+++ solib-svr4.c 26 Jan 2010 20:36:06 -0000
@@ -1307,6 +1308,26 @@ enable_break (struct svr4_info *info, in
sym_addr,
¤t_target));
+ /* On at least some versions of Solaris there's a dynamic relocation
+ on _r_debug.rtld_db_dlactivity (or however it's spelled on Solaris)
+ and SYM_ADDR may not be relocated yet, e.g., if we get control
+ before the dynamic linker has self-relocated. Check if SYM_ADDR is
+ in a known section, if it is assume we can trust its value.
+ This is just a heuristic though, it could go away or be replaced if
+ it's getting in the way.
+
+ On ARM we need to know whether the ISA of rtld_db_dlactivity (or
+ however it's spelled in your particular system) is ARM or Thumb.
+ That knowledge is encoded in the address, if it's Thumb the low bit
+ is 1. However, we've stripped that info above and it's not clear
+ what all the consequences are of passing a non-addr_bits_remove'd
+ address to create_solib_event_breakpoint. The call to
+ find_pc_section verifies we know about the address and have some
+ hope of computing the right kind of breakpoint to use (via
+ symbol info). It does mean that GDB needs to be pointed at a
+ non-stripped version of the dynamic linker in order to obtain
+ information it already knows about. Sigh. */
+
os = find_pc_section (sym_addr);
if (os != NULL)
{