[Bug translator/20423] New: improve error message for dwarf $var 'struct ... being accessed instead of member'

[Bug translator/20423] New: improve error message for dwarf $var 'struct ... being accessed instead of member'

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20423

            Bug ID: 20423
           Summary: improve error message for dwarf $var 'struct ... being
                    accessed instead of member'
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

% stap -p2 -v -e 'probe kernel.function("dput") { println(
@cast($dentry->d_inode, "struct inode")->i_count) }'

Pass 1: parsed user script and 134 library scripts using
274368virt/76604res/7412shr/69340data kb, in 160usr/10sys/172real ms.
semantic error: while processing probe kernel.function("dput@fs/dcache.c:749")
from: kernel.function("dput")

semantic error: 'struct {...}' is being accessed instead of a member: operator
'@cast' at <input>:1:42
        source: probe kernel.function("dput") { println(
@cast($dentry->d_inode, "struct inode")->i_count) }
                                                         ^


Here, i_count is a struct atomic_t { unsigned long counter; }; but systemtap's
error message doesn't help a user.  We should be printing something better than
"{...}" for the struct/type name, and we should be identifying a member of that
struct/union as an example:

semantic error: 'struct atomic_t' is being accessed instead of a member such as
'->counter': operator '@cast' at <input>:1:42

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[Bug translator/20423] improve error message for dwarf $var 'struct ... being accessed instead of member'

[jhgorse at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20423

Joseph Gorse <jhgorse at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jhgorse at gmail dot com

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[Bug translator/20423] improve error message for dwarf $var 'struct ... being accessed instead of member'

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20423

--- Comment #1 from Frank Ch. Eigler <fche at redhat dot com> ---
The error message is worse than in other cases because of

typedef struct { int counter; } atomic_t;

i.e., the struct is anonymous.

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[Bug translator/20423] improve error message for dwarf $var 'struct ... being accessed instead of member'

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20423

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Frank Ch. Eigler <fche at redhat dot com> ---
commit 9cc6246c9793

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[Bug translator/20423] improve error message for dwarf $var 'struct ... being accessed instead of member'

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20423

--- Comment #3 from Frank Ch. Eigler <fche at redhat dot com> ---
By the way, pmachata's dwgrep was worth its weight in gold ^W relearning-effort
again:

% dwgrep  /usr/src/debug/lib/modules/$VERSION/vmlinux -e 'entry ?TAG_subprogram
?AT_name (@AT_name == "dput")  child ?DW_TAG_formal_parameter @DW_AT_type
@DW_AT_type child (@AT_name == "d_inode") @DW_AT_type @DW_AT_type child
(@AT_name == "i_count") @DW_AT_type @DW_AT_type'

[29b82ac]       structure_type
        byte_size       4
        decl_file       "include/linux/types.h"
        decl_line       175
        sibling [29b82c1] typedef

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