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From: "tromey at sourceware dot org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug symtab/29779] New: ptype/o versus unions
Date: Sat, 12 Nov 2022 17:48:07 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29779

            Bug ID: 29779
           Summary: ptype/o versus unions
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: tromey at sourceware dot org
  Target Milestone: ---

ptype/o prints strange padding for a union.
You can see this in gdb itself using "ptype/o struct value".
This struct has a union:

/*      8      |      40 */    union {
/*                     8 */        CORE_ADDR address;
/*                    40 */        struct {
/*      8      |       4 */            int regnum;
/* XXX  4-byte hole      */
/*     16      |      32 */            struct frame_id {
/*     16      |       8 */                CORE_ADDR stack_addr;
/*     24      |       8 */                CORE_ADDR code_addr;
/*     32      |       8 */                CORE_ADDR special_addr;
/*     40: 0   |       4 */                frame_id_stack_status stack_stat=
us :
3;
/*     40: 3   |       4 */                unsigned int code_addr_p : 1;
/*     40: 4   |       4 */                unsigned int special_addr_p : 1;
/* XXX  3-bit hole       */
/* XXX  3-byte hole      */
/*     44      |       4 */                int artificial_depth;

                                           /* total size (bytes):   32 */
                                       } next_frame_id;

                                       /* total size (bytes):   40 */
                                   } reg;
/*                     8 */        internalvar *internalvar;
/*                     8 */        xmethod_worker *xm_worker;
/*                    16 */        struct {
/*      8      |       8 */            const lval_funcs *funcs;
/*     16      |       8 */            void *closure;

                                       /* total size (bytes):   16 */
                                   } computed;
/* XXX 32-byte padding   */

                                   /* total size (bytes):   40 */
                               } location;


I'm not sure what the "32-byte padding" refers to -- maybe the maximum
padding of all union members?
Anyway it would probably be more useful to see the amount of padding
per-member, and then if the maximum were shown, the comment could
explain that explicitly.

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