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[PATCH] Handle absence of DT_DEBUG while debugging ld.so
- From: Luis Machado <luisgpm at linux dot vnet dot ibm dot com>
- To: gdb-patches at sourceware dot org
- Date: Mon, 28 Jul 2008 20:54:37 -0300
- Subject: [PATCH] Handle absence of DT_DEBUG while debugging ld.so
- Reply-to: luisgpm at linux dot vnet dot ibm dot com
Hi folks,
When trying to debug ld.so, we may find that the DT_DEBUG entry in
the .dynamic section is missing, thus GDB tries to look for the _r_debug
minimal symbol, and eventually finds it. This works OK as long as the
_r_debug minimal symbol is correct and initialized.
In the case where GDB fetches an uninitialized _r_debug minimal symbol
and tries to access its address, we have a memory access error, just
like below:
(gdb) r
Starting program: /foo/lib/ld.so.1
Cannot access memory at address 0x2f648
Thus, we should guard this piece of code against uninitialized addresses
so that GDB can skip this entry and look for another (hopefully) valid
_r_debug symbol.
Tested against HEAD for ppc32/ppc64 with no regressions. OK?
Regards,
Luis
---
2008-07-28 Luis Machado <luisgpm@br.ibm.com>
* solib-svr4.c (elf_locate_base): Check if msymbol's
address is valid.
Index: gdb/solib-svr4.c
===================================================================
--- gdb.orig/solib-svr4.c 2008-07-28 14:35:20.000000000 -0700
+++ gdb/solib-svr4.c 2008-07-28 16:11:42.000000000 -0700
@@ -508,9 +508,14 @@
return dyn_ptr;
/* This may be a static executable. Look for the symbol
- conventionally named _r_debug, as a last resort. */
+ conventionally named _r_debug, as a last resort and check if
+ the address contained in the minimal symbol is valid before
+ proceeding. */
msymbol = lookup_minimal_symbol ("_r_debug", NULL, symfile_objfile);
- if (msymbol != NULL)
+ if (msymbol != NULL
+ && !target_read_memory (SYMBOL_VALUE_ADDRESS (msymbol),
+ (gdb_byte *)&dyn_ptr,
+ TYPE_LENGTH (builtin_type_void_data_ptr)))
return SYMBOL_VALUE_ADDRESS (msymbol);
/* DT_DEBUG entry not found. */