From f714c56f3cd13a9216000951f4319250734fc0ae Mon Sep 17 00:00:00 2001 From: Tom de Vries Date: Mon, 9 Mar 2026 17:33:47 +0100 Subject: [PATCH 8/8] [gdb] Enable ptype /o for some dynamic types Printing the offsets of a struct containing a flexible array member using "ptype /o" currently fails: ... $ cat test.c struct s { int a; int b[]; }; struct s foo; $ gcc -g test.c -c $ gdb -q -batch test.o -ex "ptype /o struct s" warning: ptype/o does not work with dynamic types; disabling '/o' type = struct s { int a; int b[]; } ... This has been the case since gdb 14, containing commit 0c1aa2a0953 ("Disable ptype/o for dynamic types"). If we revert the commit, we get instead: ... $ gdb -q -batch test.o -ex "ptype /o struct s" /* offset | size */ type = struct s { /* 0 | 4 */ int a; /* 4 | 0 */ int b[]; /* total size (bytes): 4 */ } ... which is similar to what pahole prints: ... struct s { int a; /* 0 4 */ int b[]; /* 4 0 */ /* size: 4, cachelines: 1, members: 2 */ /* last cacheline: 4 bytes */ }; ... The problem is that the commit uses is_dynamic_type: ... if (flags.print_offsets && is_dynamic_type (type)) { warning (_("ptype/o does not work with dynamic types; disabling '/o'")); flags.print_offsets = 0; } ... which is too restrictive. Fix this by using a new function cannot_print_offsets instead. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33966 --- gdb/gdbtypes.c | 39 ++++++++++++-- gdb/gdbtypes.h | 4 ++ gdb/testsuite/gdb.ada/ptype-o.exp | 2 +- gdb/testsuite/gdb.base/ptype-offsets-c.c | 37 +++++++++++++ gdb/testsuite/gdb.base/ptype-offsets-c.exp | 63 ++++++++++++++++++++++ gdb/typeprint.c | 4 +- 6 files changed, 143 insertions(+), 6 deletions(-) create mode 100644 gdb/testsuite/gdb.base/ptype-offsets-c.c create mode 100644 gdb/testsuite/gdb.base/ptype-offsets-c.exp diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c index 3dc2308f14e..b2660a4d1b3 100644 --- a/gdb/gdbtypes.c +++ b/gdb/gdbtypes.c @@ -2035,10 +2035,11 @@ array_type_has_dynamic_stride (struct type *type) return prop != nullptr && prop->is_constant (); } -/* Worker for is_dynamic_type. */ +/* Worker for is_dynamic_type/cannot_print_offsets. */ static bool -is_dynamic_type_internal_1 (struct type *type) +is_dynamic_type_internal_1 (struct type *type, + bool cannot_print_offsets_p = false) { type = check_typedef (type); @@ -2112,7 +2113,24 @@ is_dynamic_type_internal_1 (struct type *type) continue; /* If the field has dynamic type, then so does TYPE. */ if (is_dynamic_type_internal_1 (f.type ())) - return true; + { + bool last_struct_field_p + = (type->code () == TYPE_CODE_STRUCT + && i == type->num_fields () - 1); + if (cannot_print_offsets_p && last_struct_field_p) + { + if (f.type ()->code () == TYPE_CODE_STRUCT) + /* The last field is a dynamic type and a struct. Check + if we can print the offsets for the struct. */ + return is_dynamic_type_internal_1 (f.type (), true); + + /* The last field is a dynamic type, this is ok to print + offsets for. */ + return false; + } + + return true; + } /* If the field is at a fixed offset, then it is not dynamic. */ if (f.loc_kind () != FIELD_LOC_KIND_DWARF_BLOCK) @@ -2155,6 +2173,21 @@ is_dynamic_type (struct type *type) return is_dynamic_type_internal (type, true); } +/* See gdbtypes.h. */ + +bool +cannot_print_offsets (struct type *type) +{ + type = check_typedef (type); + + /* We only want to recognize references and pointers at the outermost + level. */ + if (type->is_pointer_or_reference ()) + type = check_typedef (type->target_type ()); + + return is_dynamic_type_internal_1 (type, true); +} + static struct type *resolve_dynamic_type_internal (struct type *type, struct property_addr_info *addr_stack, const frame_info_ptr &frame, bool top_level); diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h index 8b00fec59a1..9a745ca3e02 100644 --- a/gdb/gdbtypes.h +++ b/gdb/gdbtypes.h @@ -2629,6 +2629,10 @@ extern struct type *resolve_dynamic_type "dynamic". */ extern bool is_dynamic_type (struct type *type); +/* Return true if TYPE cannot be printed using ptype /o. */ + +extern bool cannot_print_offsets (struct type *type); + extern struct type *check_typedef (struct type *); extern void check_stub_method_group (struct type *, int); diff --git a/gdb/testsuite/gdb.ada/ptype-o.exp b/gdb/testsuite/gdb.ada/ptype-o.exp index 5038ee171d2..7f3ec3ce7a3 100644 --- a/gdb/testsuite/gdb.ada/ptype-o.exp +++ b/gdb/testsuite/gdb.ada/ptype-o.exp @@ -37,7 +37,7 @@ foreach_gnat_encoding scenario flags {all minimal} { "Warning: the current language does not match this frame." if {$scenario == "minimal"} { - set exp "ptype/o does not work with dynamic types.*" + set exp "ptype/o does not work with this dynamic type.*" } else { # In "all" mode this prints nonsense, but at least does not # crash. diff --git a/gdb/testsuite/gdb.base/ptype-offsets-c.c b/gdb/testsuite/gdb.base/ptype-offsets-c.c new file mode 100644 index 00000000000..74ac9ed7b37 --- /dev/null +++ b/gdb/testsuite/gdb.base/ptype-offsets-c.c @@ -0,0 +1,37 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2026 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +struct flexible_array_member +{ + int an_int; + int fam[]; +}; + +struct nested_flexible_array_member +{ + int another_int; + struct flexible_array_member sfam; +}; + +int +main (void) +{ + struct flexible_array_member fam; + struct nested_flexible_array_member nfam; + + return 0; +} diff --git a/gdb/testsuite/gdb.base/ptype-offsets-c.exp b/gdb/testsuite/gdb.base/ptype-offsets-c.exp new file mode 100644 index 00000000000..cffcbbeb2f7 --- /dev/null +++ b/gdb/testsuite/gdb.base/ptype-offsets-c.exp @@ -0,0 +1,63 @@ +# This testcase is part of GDB, the GNU debugger. + +# Copyright 2026 Free Software Foundation, Inc. + +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . + +# This testcase exercises the "ptype /o" feature, which can be used to +# print the offsets and sizes of each field of a struct/union. +# +# This is similar to ptype-offsets.exp, which uses C++ instead of C. + +standard_testfile .c + +# Test only works on LP64 targets. That's how we guarantee that the +# expected holes will be present in the struct. +if { ![is_lp64_target] } { + untested "test work only on lp64 targets" + return 0 +} + +if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } { + return -1 +} + +# Tests handling flexible array member. Regression tests for PR gdb/33966. +set l { + "ptype /o struct flexible_array_member" + "/* offset | size */ type = struct flexible_array_member {" + "/* 0 | 4 */ int an_int;" + "/* 4 | 0 */ int fam[];" + "" + " /* total size (bytes): 4 */" + " }" +} +gdb_test "ptype /o struct flexible_array_member" \ + [string_to_regexp [multi_line {*}$l]] + +set l { + "/* offset | size */ type = struct nested_flexible_array_member {" + "/* 0 | 4 */ int another_int;" + "/* 4 | 4 */ struct flexible_array_member {" + "/* 4 | 4 */ int an_int;" + "/* 8 | 0 */ int fam[];" + "" + " /* total size (bytes): 4 */" + " } sfam;" + "" + " /* total size (bytes): 8 */" + " }" +} +gdb_test "ptype /o struct nested_flexible_array_member" \ + [string_to_regexp [multi_line {*}$l]] diff --git a/gdb/typeprint.c b/gdb/typeprint.c index 6494103ba93..e7019a378f3 100644 --- a/gdb/typeprint.c +++ b/gdb/typeprint.c @@ -452,9 +452,9 @@ whatis_exp (const char *exp, int show) type = val->type (); } - if (flags.print_offsets && is_dynamic_type (type)) + if (flags.print_offsets && cannot_print_offsets (type)) { - warning (_("ptype/o does not work with dynamic types; disabling '/o'")); + warning (_("ptype/o does not work with this dynamic type; disabling '/o'")); flags.print_offsets = 0; } -- 2.51.0