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From: sergiodj+buildbot@redhat.com To: gdb-testers@sourceware.org Subject: [binutils-gdb] error/internal-error printing local variable during "bt full". Date: Mon, 23 Nov 2015 19:54:00 -0000 [thread overview] Message-ID: <16c3b12f199a7ec99a0b51bd83b66942547bba87@gdb-build> (raw) *** TEST RESULTS FOR COMMIT 16c3b12f199a7ec99a0b51bd83b66942547bba87 *** Author: Joel Brobecker <brobecker@adacore.com> Branch: master Commit: 16c3b12f199a7ec99a0b51bd83b66942547bba87 error/internal-error printing local variable during "bt full". One of our users reported an internal error using the "bt full" command. In their situation, reproducing involved the following scenario: (gdb) frame 1 (gdb) bt full #0 0xf7783430 in __kernel_vsyscall () No symbol table info available. #1 0xf5550aeb in waitpid () at ../sysdeps/unix/syscall-template.S:81 No locals. [...] #6 0x0fe83139 in xxxx (arg=...) [...some locals printed, and then...] <S17b> = [...]/dwarf2loc.c:364: internal-error: dwarf_expr_frame_base: Assertion `framefunc != NULL' failed. As shown above, the error happens while GDB is trying to print the value of <S17b>, which is a local string internally generated by the compiler. For that, it finds that the array lives in memory, and therefore tries to create a struct value for it via: case DWARF_VALUE_MEMORY: { CORE_ADDR address = dwarf_expr_fetch_address (ctx, 0); [...] retval = value_at_lazy (type, address + byte_offset); Unfortunately for us, TYPE happens to be an array whose bounds are dynamic. More precisely, the bounds of our arrays are described in the debugging info as being... <4><2c1985e>: Abbrev Number: 33 (DW_TAG_subrange_type) <2c1985f> DW_AT_type : <0x2c1989c> <2c19863> DW_AT_lower_bound : <0x2c19835> <2c19867> DW_AT_upper_bound : <0x2c19841> ... which are references to a pair of local variables. For instance, the lower bound is a reference to the following DIE <3><2c19835>: Abbrev Number: 32 (DW_TAG_variable) <2c19836> DW_AT_name : [...] <2c1983a> DW_AT_type : <0x2c198b4> <2c1983e> DW_AT_artificial : 1 <2c1983e> DW_AT_location : 2 byte block: 91 58 (DW_OP_fbreg: -40) As a result of the above, value_at_lazy indirectly triggers a resolution of TYPE (via value_from_contents_and_address), which means a resolution of TYPE's bounds, and as seen in the DW_AT_location attribute above for our bounds, computing the bound's location requires the frame (its location expression uses DW_OP_fbreg). Unfortunately for us, value_at_lazy does not get passed a frame, we've lost the relevant frame when we try to resolve the array's bounds. Instead, resolve_dynamic_range gets calls dwarf2_evaluate_property with NULL as the frame: static struct type * resolve_dynamic_range (struct type *dyn_range_type, struct property_addr_info *addr_stack) { [...] if (dwarf2_evaluate_property (prop, NULL, addr_stack, &value)) ^^^^ ... which then handles this by using the selected frame instead: if (frame == NULL && has_stack_frames ()) frame = get_selected_frame (NULL); In our case, the selected frame happens to be frame #1, which is a frame where we have a minimal amount of debugging info, and in particular, no debug info for the function itself. And because of that, when we try to determine the frame's base... static void dwarf_expr_frame_base (void *baton, const gdb_byte **start, size_t * length) { struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton; const struct block *bl = get_frame_block (debaton->frame, NULL); [...] framefunc = block_linkage_function (bl); ... framefunc ends up being NULL, which triggers the assert in that same function: gdb_assert (framefunc != NULL); This patches avoids the issue by temporarily setting the selected_frame before printing the locals of each frames. This patch also adds a small testcase, which reproduces the same issue, but with a slightly different outcome: (gdb) bt full #0 0x000000000040049a in opaque_routine () No symbol table info available. #1 0x0000000000400532 in main () at wrong_frame_bt_full-main.c:20 my_table_size = 3 my_table = <error reading variable my_table (frame address is not available.)> With this patch, the output becomes: (gdb) bt full [...] my_table = {0, 1, 2} gdb/ChangeLog: * stack.c (print_frame_local_vars): Temporarily set the selected frame to FRAME while printing the frame's local variables. gdb/testsuite/ChangeLog: * gdb.base/wrong_frame_bt_full-main.c: New file. * gdb.base/wrong_frame_bt_full-opaque.c: New file. * gdb.base/wrong_frame_bt_full.exp: New file.
next reply other threads:[~2015-11-23 19:54 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-11-23 19:54 sergiodj+buildbot [this message] 2015-11-23 19:57 ` Failures on Debian-s390x-native-gdbserver-m64, branch master sergiodj+buildbot 2015-11-23 20:14 ` Failures on Debian-s390x-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-23 20:43 ` Failures on AIX-POWER7-plain, " sergiodj+buildbot 2015-11-23 22:19 ` Failures on Fedora-s390x-m64, " sergiodj+buildbot 2015-11-23 22:51 ` Failures on Fedora-x86_64-native-extended-gdbserver-m32, " sergiodj+buildbot 2015-11-23 23:13 ` Failures on Fedora-x86_64-native-gdbserver-m64, " sergiodj+buildbot 2015-11-23 23:38 ` Failures on Debian-i686-native-gdbserver, " sergiodj+buildbot 2015-11-24 0:39 ` Failures on Fedora-ppc64be-m64, " sergiodj+buildbot 2015-11-24 0:54 ` Failures on Fedora-ppc64be-native-gdbserver-m64, " sergiodj+buildbot 2015-11-24 1:14 ` Failures on Fedora-ppc64be-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-24 2:58 ` Failures on Fedora-ppc64le-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-24 3:31 ` Failures on Fedora-ppc64le-native-gdbserver-m64, " sergiodj+buildbot
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