1257148 - [Static Analysis][Excessive padding] In structure txEXSLTFunctionDescriptor

Status: RESOLVED FIXED

(Core :: XSLT, defect)

Description

[Andi [:andi]]

The Static Analysis tool scan-build added that excessive padding is added to structure txEXSLTFunctionDescriptor when compiled on 64bit system. 

>>	struct txEXSLTFunctionDescriptor
>>	{
>>	    int8_t mMinParams;
>>	    int8_t mMaxParams;
>>	    Expr::ResultType mReturnType;
>>	    nsIAtom** mName;
>>	    int32_t mNamespaceID;
>>	    const char* mNamespaceURI;
>>	};

This is due to the fact than on 64bit systems pointer size is 8bytes and without proper ordering this structure weighs in 32bytes, this is because two alignment paddings, of 4 bytes each, are added after |mReturnType| and |mNamespaceID| in order to align pointers that follow, ideally the size of this is 24 byes:

>>struct txEXSLTFunctionDescriptor
>>{
>>    int8_t mMinParams;
>>    int8_t mMaxParams;
>>    Expr::ResultType mReturnType;
>>    int32_t mNamespaceID;
>>    nsIAtom** mName;
>>    const char* mNamespaceURI;
>>};

The size of the structure is specially important on ARM devices that have low cache levels and as we have the same code-debase with fennec/Android i think this should be very useful to solve now for the time when we will distribute 64bit arm binaries.

Comment 1

[Andi [:andi]]

Attachment: MozReview Request: Bug 1257148 - correctly align structure txEXSLTFunctionDescriptor. r?peterv

Review commit: https://reviewboard.mozilla.org/r/40425/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/40425/

Comment 2

[Peter Van der Beken [:peterv]]

Comment on attachment 8731199 [details]
MozReview Request: Bug 1257148 - correctly align structure txEXSLTFunctionDescriptor. r?peterv

https://reviewboard.mozilla.org/r/40425/#review37453

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9f11935709f6

Comment 4

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/9f11935709f6