b7874836c3
In PR gdb/27059 an issue was discovered where GDB would sometimes trigger undefined behaviour in the form of signed integer overflow. The problem here is that GDB was reading random garbage from the inferior memory space, assuming this data was valid, and performing arithmetic on it. This bug raises an interesting general problem with GDB's DWARF expression evaluator, which is this: We currently assume that the DWARF expressions being evaluated are well formed, and well behaving. As an example, this is the expression that the bug was running into problems on, this was used as the expression for a DW_AT_byte_stride of a DW_TAG_subrange_type: DW_OP_push_object_address; DW_OP_plus_uconst: 88; DW_OP_deref; DW_OP_push_object_address; DW_OP_plus_uconst: 32; DW_OP_deref; DW_OP_mul Two values are read from the inferior and multiplied together. GDB should not assume that any value read from the inferior is in any way sane, as such the implementation of DW_OP_mul should be guarding against overflow and doing something semi-sane here. However, it turns out that the original bug PR gdb/27059, is hitting a more specific case, which doesn't require changes to the DWARF expression evaluator, so I'm going to leave the above issue for another day. In the test mentioned in the bug GDB is actually trying to resolve the dynamic type of a Fortran array that is NOT allocated. A non-allocated Fortran array is one that does not have any data allocated for it yet, and even the upper and lower bounds of the array are not yet known. It turns out that, at least for gfortran compiled code, the data fields that describe the byte-stride are not initialised until the array is allocated. This leads me to the following conclusion: GDB should not try to resolve the bounds, or stride information for an array that is not allocated (or not associated, a similar, but slightly different Fortran feature). Instead, each of these properties should be set to undefined if the array is not allocated (or associated). That is what this commit does. There's a new flag that is passed around during the dynamic array resolution. When this flag is true the dynamic properties are resolved using the DWARF expressions as they currently are, but when this flag is false the expressions are not evaluated, and instead the properties are set to undefined. gdb/ChangeLog: PR gdb/27059 * eval.c (evaluate_subexp_for_sizeof): Handle not allocated and not associated arrays. * f-lang.c (fortran_adjust_dynamic_array_base_address_hack): Don't adjust arrays that are not allocated/associated. * gdbtypes.c (resolve_dynamic_range): Update header comment. Add new parameter which is used to sometimes set dynamic properties to undefined. (resolve_dynamic_array_or_string): Update header comment. Add new parameter which is used to guard evaluating dynamic properties. Resolve allocated/associated properties first. gdb/testsuite/ChangeLog: PR gdb/27059 * gdb.dwarf2/dyn-type-unallocated.c: New file. * gdb.dwarf2/dyn-type-unallocated.exp: New file. |
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README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.