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From: "Ralf Habacker" <Ralf DOT Habacker AT freenet DOT de>
To: <kde-cygwin AT mail DOT kde DOT org>, "Charles Wilson" <cwilson AT ece DOT gatech DOT edu>,
   "Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
Cc: "Binutils" <binutils AT sources DOT redhat DOT com>,
   "Cygwin-Apps" <cygwin-apps AT cygwin DOT com>
Subject: RE: ordinal linking for cygwin ld
Date: Sat, 27 Apr 2002 14:47:16 +0200
Message-ID: <000701c1ede9$a9274310$d36707d5@BRAMSCHE>
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> Well then, this is only half the puzzle. I can see what you gain from
> such a patch, but as Chuck as indicated, it will cause -major-
> difficulties in management.

Do you have read the rules I have stated for kde ?

> A patch to use hint ordinals when linking by name would be _very_ useful
> though, as that would
> a) give the performance benefit you are looking for
> b) allow backward compatible library versioning as link-by-name does.
>
> We'd probably also need to ensure that strip leaves the names in the IAT
> (I wasn't clear from your other email whether it does that or not).
>
Yes it does. See some parts about my auto-import documentation.

$ objdump -x client.exe

<snip>
The Import Tables (interpreted .idata section contents)


  vma:            Hint    Time      Forward  DLL       First
                  Table   Stamp     Chain    Name      Thunk
(1) 00004000     00004068 00000000 00000000 000041a8 000040b4
                   |(3)                                   |(2)
                   |            _nm_....  (4)        IAT  |  _imp_...
                +------+        +------------+        +------+
                |  (6)----+---->| Hint 16bit |(7)<------     |
                +------+  |     +------------+        +------+
                |      |  |     | membername |(8)     +------+
                +------+  |     +------------+        +------+
                          |                           +------+
                          |      _nm_...  (5)         +------+
                          |     +-------------+       +------+
                          +---->|Ordinal 16bit|(7)    +------+
                                +-------------+
                                | 0x00 0x80   |
                                +-------------+

(1) is the IMAGE_IMPORT_DESCRIPTOR.

FirstThunk (2) points to the import address table (IAT), which entries are
identifed by corresponding _imp_... symbols.

HintTab (3) point to a rva (relative virtual address = offset from image start)
vector pointing to IMAGE_IMPORT_BY_NAME unions.

(4) shows an IMAGE_IMPORT_BY_NAME union for a named link. It is identifed by the
_nm_<smbol> name .
In this structure the symbol name string is stored independed from the regular
symbol name, which can be only stripped.

(5) shows a IMAGE_IMPORT_BY_NAME union for a ordinal link.

Now see the relating objdump part. The numbers 6,7,8 identify the related
structure element.

        DLL Name: dll.dll
        vma:  Hint/Ord Member-Name
         (6)       (7)     (8)
        40f4        0  printfunc0000__1Av
        410c        1  var0000


00404290 <__nm__var0000>:
  404290:	01 00
  404292:	76 61
  404294:	72 30
  404296:	30 30
  404298:	30 00


No see this for an auto-imported data

  vma:            Hint    Time      Forward  DLL       First
                  Table   Stamp     Chain    Name      Thunk
 00004000       00004068 00000000 00000000 000041a8 00001064
                   |(3)                                 |(2)
              nm_thnk_...       _nm_...  (4)            |
                +------+        +------------+        __fu0_...
                |  (6)----+---->| Hint 16bit |(7)     points directly into the
text segement
                +------+  |     +------------+        to the relating
instructions address
                |      |  |     | Membername |(8)
                +------+  |     +------------+
                          |
                          |     _nm_...  (5)
                          |     +-------------+
                          +---->|Ordinal 16bit|(7)
                                +-------------+
                                | 0x00 0x80   |
                                +-------------+

It's the same as above except

(2) points directly into the text segement to the relating instructions address.
    The target is identified by the __fu0_<symbol> name. See a sample below.

    0xa1 is the instruction at offset 0x401063, the address starts at 0x0401063.

  401063:	a1 b8 40 40 00       	mov    0x4040b8,%eax
               ^^^^^^^^^^^
00401064 <__fu0__var0000>:
      ^^

(3) HintTab is identifed by the _nm_thnk_<symbol>.


004040a8 <__nm_thnk__var0000>:
  4040a8:       02 00
  4040aa:       00 80 00 00 00 00


Hope that helps
Ralf