SLAU131V October   2004  – February 2020

 

  1.   1
    1.     2
    2.     3
    3.     4
    4.     5
    5.     6
  2.   7
    1.     8
    2.     9
  3.   10
    1.     11
    2.     12
    3.     13
      1.      14
    4.     15
      1.      16
      2.      17
      3.      18
      4.      19
        1.       20
        2.       21
      5.      22
      6.      23
      7.      24
    5.     25
      1.      26
      2.      27
    6.     28
      1.      29
      2.      30
      3.      31
      4.      32
    7.     33
      1.      34
      2.      35
    8.     36
  4.   37
    1.     38
      1.      39
      2.      40
        1.       41
        2.       42
        3.       43
        4.       44
        5.       45
          1.        46
    2.     47
    3.     48
      1.      49
      2.      50
        1.       51
        2.       52
        3.       53
      3.      54
        1.       55
        2.       56
    4.     57
    5.     58
    6.     59
  5.   60
    1.     61
    2.     62
    3.     63
    4.     64
    5.     65
      1.      66
      2.      67
    6.     68
      1.      69
      2.      70
      3.      71
        1.       72
      4.      73
    7.     74
      1.      75
        1.       76
        2.       77
        3.       78
        4.       79
        5.       80
      2.      81
      3.      82
    8.     83
      1.      84
      2.      85
      3.      86
        1.       87
      4.      88
      5.      89
      6.      90
      7.      91
      8.      92
      9.      93
    9.     94
      1.      95
      2.      96
      3.      97
    10.     98
      1.      99
      2.      100
    11.     101
    12.     102
      1.      103
      2.      104
    13.     105
      1.      106
  6.   107
    1.     108
    2.     109
      1.      110
    3.     111
    4.     112
    5.     113
    6.     114
    7.     115
    8.     116
    9.     117
    10.     118
    11.     119
    12.     120
  7.   121
    1.     122
    2.     123
      1.      124
    3.     125
      1.      126
      2.      127
        1.       128
        2.       129
      3.      130
      4.      131
      5.      132
      6.      133
      7.      134
        1.       135
      8.      136
      9.      137
      10.      138
      11.      139
    4.     140
    5.     141
      1.      142
      2.      143
      3.      144
    6.     145
      1.      146
    7.     147
      1.      148
    8.     149
    9.     150
      1.      151
      2.      152
    10.     153
  8.   154
    1.     155
    2.     156
    3.     157
    4.     158
      1.      159
    5.     160
      1.      161
      2.      162
      3.      163
      4.      164
  9.   165
    1.     166
    2.     167
    3.     168
    4.     169
      1.      170
      2.      171
      3.      172
        1.       173
        2.       174
        3.       175
      4.      176
      5.      177
      6.      178
      7.      179
      8.      180
      9.      181
      10.      182
      11.      183
      12.      184
      13.      185
      14.      186
      15.      187
        1.       188
        2.       189
        3.       190
      16.      191
        1.       192
      17.      193
      18.      194
      19.      195
      20.      196
      21.      197
      22.      198
      23.      199
      24.      200
      25.      201
      26.      202
      27.      203
      28.      204
      29.      205
      30.      206
      31.      207
      32.      208
      33.      209
      34.      210
      35.      211
    5.     212
      1.      213
      2.      214
      3.      215
      4.      216
      5.      217
      6.      218
        1.       219
        2.       220
          1.        221
        3.       222
          1.        223
      7.      224
        1.       225
          1.        226
        2.       227
          1.        228
          2.        229
          3.        230
          4.        231
            1.         232
            2.         233
          5.        234
          6.        235
        3.       236
          1.        237
        4.       238
        5.       239
          1.        240
        6.       241
        7.       242
      8.      243
        1.       244
        2.       245
          1.        246
          2.        247
      9.      248
        1.       249
          1.        250
        2.       251
          1.        252
          2.        253
        3.       254
        4.       255
          1.        256
        5.       257
        6.       258
      10.      259
      11.      260
        1.       261
        2.       262
        3.       263
      12.      264
        1.       265
        2.       266
        3.       267
        4.       268
        5.       269
        6.       270
        7.       271
          1.        272
          2.        273
          3.        274
          4.        275
        8.       276
      13.      277
        1.       278
        2.       279
        3.       280
        4.       281
    6.     282
      1.      283
      2.      284
      3.      285
    7.     286
      1.      287
      2.      288
      3.      289
    8.     290
      1.      291
      2.      292
      3.      293
        1.       294
      4.      295
        1.       296
        2.       297
        3.       298
        4.       299
          1.        300
        5.       301
          1.        302
        6.       303
          1.        304
          2.        305
      5.      306
        1.       307
        2.       308
        3.       309
        4.       310
        5.       311
      6.      312
        1.       313
      7.      314
        1.       315
    9.     316
      1.      317
      2.      318
      3.      319
        1.       320
        2.       321
        3.       322
        4.       323
      4.      324
        1.       325
      5.      326
    10.     327
    11.     328
      1.      329
      2.      330
      3.      331
      4.      332
      5.      333
    12.     334
      1.      335
      2.      336
  10.   337
    1.     338
    2.     339
    3.     340
      1.      341
      2.      342
  11.   343
    1.     344
    2.     345
    3.     346
      1.      347
  12.   348
    1.     349
    2.     350
    3.     351
    4.     352
  13.   353
    1.     354
    2.     355
      1.      356
      2.      357
    3.     358
      1.      359
      2.      360
      3.      361
      4.      362
    4.     363
      1.      364
      2.      365
        1.       366
        2.       367
    5.     368
    6.     369
      1.      370
      2.      371
    7.     372
    8.     373
    9.     374
      1.      375
      2.      376
      3.      377
    10.     378
    11.     379
    12.     380
    13.     381
      1.      382
      2.      383
      3.      384
      4.      385
      5.      386
      6.      387
        1.       388
  14.   389
    1.     390
    2.     391
      1.      392
      2.      393
      3.      394
      4.      395
      5.      396
      6.      397
      7.      398
      8.      399
      9.      400
      10.      401
      11.      402
      12.      403
      13.      404
      14.      405
      15.      406
      16.      407
    3.     408
      1.      409
      2.      410
      3.      411
      4.      412
    4.     413
      1.      414
      2.      415
      3.      416
      4.      417
      5.      418
      6.      419
      7.      420
  15.   421
    1.     422
    2.     423
  16.   424
    1.     425
    2.     426
      1.      427
        1.       428
      2.      429
        1.       430
      3.      431
        1.       432
      4.      433
        1.       434
      5.      435
        1.       436
      6.      437
        1.       438
      7.      439
        1.       440
  17.   441
    1.     442
      1.      443
    2.     444
      1.      445
      2.      446
      3.      447
      4.      448
      5.      449
      6.      450
  18.   451
    1.     452
  19.   453
    1.     454

2.6.3 Weak Symbols

Weak symbols are symbols that may or may not be defined.

The linker processes symbols that are defined with a "weak" binding differently from symbols that are defined with global binding. Instead of including a weak symbol in the object file's symbol table (as it would for a global symbol), the linker only includes a weak symbol in the output of a "final" link if the symbol is required to resolve an otherwise unresolved reference.

This allows the linker to minimize the number of symbols it includes in the output file's symbol table by omitting those that are not needed to resolve references. Reducing the size of the output file's symbol table reduces the time required to link, especially if there are a large number of pre-loaded symbols to link against. This feature is particularly helpful for OpenCL applications.

You can define a weak symbol using either the .weak assembly directive or the weak operator in the linker command file.

  • Using Assembly: To define a weak symbol in an input object file, the source file can be written in assembly. Use the .weak and .set directives in combination as shown in the following example, which defines a weak symbol "ext_addr_sym":
    • .weak ext_addr_sym ext_addr_sym .set 0x12345678

    Assemble the source file that defines weak symbols, and include the resulting object file in the link. The "ext_addr_sym" in this example is available as a weak symbol in a final link. It is a candidate for removal if the symbol is not referenced elsewhere in the application. See .weak directive.

  • Using the Linker Command File: To define a weak symbol in a linker command file, use the "weak" operator in an assignment expression to designate that the symbol as eligible for removal from the output file's symbol table if it is not referenced. In a linker command file, an assignment expression outside a MEMORY or SECTIONS directive can be used to define a weak linker-defined symbol. For example, you can define "ext_addr_sym" as follows:
    • weak(ext_addr_sym) = 0x12345678;

    If the linker command file is used to perform the final link, then "ext_addr_sym" is presented to the linker as a weak symbol; it will not be included in the resulting output file if the symbol is not referenced. See Section 8.6.2.

  • Using C/C++ code: See information about the WEAK pragma and weak GCC-style variable attribute in the MSP430 Optimizing C/C++ Compiler User's Guide.

If there are multiple definitions of the same symbol, the linker uses certain rules to determine which definition takes precedence. Some definitions may have weak binding and others may have strong binding. "Strong" in this context means that the symbol has not been given a weak binding by either of the two methods described above. Some definitions may come from an input object file (that is, using assembly directives) and others may come from an assignment statement in a linker command file.

The linker uses the following guidelines to determine which definition is used when resolving references to a symbol:

  • A strongly bound symbol always takes precedence over a weakly bound symbol.
  • If two symbols are both strongly bound or both weakly bound, a symbol defined in a linker command file takes precedence over a symbol defined in an input object file.
  • If two symbols are both strongly bound and both are defined in an input object file, the linker provides a symbol redefinition error and halts the link process.