[PATCH] D128148: [XCOFF] write the aux header when the visibility is specified in XCOFF32.

[Esme Yi via Phabricator via llvm-commits]

Esme added inline comments.


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Comment at: llvm/include/llvm/BinaryFormat/XCOFF.h:34
 constexpr size_t AuxFileHeaderSize64 = 110;
+constexpr size_t AuxFileHeaderSizeObj = 28;
 constexpr size_t SectionHeaderSize32 = 40;
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DiggerLin wrote:
> not sure how the size 28 come from ?
>   Some AIX programs generate auxiliary headers for 32-bit object files that end after the data_start field.  The macro _AOUTHSZ_SHORT defines the length of such a header.

As I replied in the next comment, the value of _AOUTHSZ_SHORT here is 28.
Well, changing `AuxFileHeaderSizeObj` to `AuxFileHeaderSizeShort` might be more appropriate?


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Comment at: llvm/lib/MC/XCOFFObjectWriter.cpp:309
   size_t auxiliaryHeaderSize() const {
-    assert(!needsAuxiliaryHeader() &&
-           "Auxiliary header support not implemented.");
-    return 0;
+    return HasVisibility && !is64Bit() ? XCOFF::AuxFileHeaderSizeObj : 0;
   }
----------------
DiggerLin wrote:
> according to "The auxiliary header contains system-dependent and implementation-dependent information, in which is used for loading and executing a module. Information in the auxiliary header minimizes how much of the file must be processed by the system loader at execution time." in  https://www.ibm.com/docs/en/aix/7.2?topic=formats-xcoff-object-file-format#XCOFF__fyovh386shar
> 
> the auxiliaryHeaderSize should not depend on the HasVisibility 
Thank you for your comments!
Generally, the auxiliary header should not be required by an un-executable object file. However, it may be needed in some specific cases, like the visibility case here.
Here is a related description in /usr/include/aouthdr.h of AIX.

>   In general, the auxiliary header can be any size, and the length of the auxiliary in any particular object file is specified in the f_opthdr field of the XCOFF header.
>   Some AIX programs generate auxiliary headers for 32-bit object files that end after the data_start field.  The macro _AOUTHSZ_SHORT defines the length of such a header.  No auxiliary header is required for an object file that is not an executable.



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  https://reviews.llvm.org/D128148/new/

https://reviews.llvm.org/D128148