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Thread-Topic: [PATCH 2/2] Documentation Update. 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Based on the discussion so far, I have the following plan for resolving thi= s issue: In GCC13: 1. Add documentation in extend.texi to include all the following 3 cases as= GCC extension: Case 1: The structure with a flexible array member is the last field of ano= ther structure, for example: struct flex { int length; char data[]; } struct out_flex { int m; struct flex flex_data; } In the above, flex_data.data[] is considered as a flexible array too. Case 2: The structure with a flexible array member is the field of another = union, for example: struct flex1 { int length1; char data1[]; } struct flex2 { int length2; char data2[]; } union out_flex { struct flex1 flex_data1; struct flex2 flex_data2; } In the above, flex_data1.data1[] or flex_data2.data2[] is considered as fle= xible arrays too. Case 3: The structure with a flexible array member is the middle field of a= nother structure, for example: struct flex { int length; char data[]; } struct out_flex { int m; struct flex flex_data; int n; } In the above, flex_data.data[] is allowed to be extended flexibly to the padding. E.g, up to 4 elements. However, relying on space in struct padding is a bad programming practice, = compilers do not=20 handle such extension consistently, and any code relying on this behavior s= hould be modified to ensure that flexible array members only end up at the ends of structures= . Please use warning option -Wgnu-variable-sized-type-not-at-end (to be consi= stent with CLANG)=20 to identify all such cases in the source code and modify them. This extensi= on will be deprecated from gcc in the next release. 2. Add a new warning option -Wgnu-varaible-sized-type-not-at-end to warn su= ch usage. In GCC14: 1. Include this new warning -Wgnu-varaible-sized-type-not-at-end to -Wall 2. Deprecate this extension from GCC. (Or delay this to next release?). Let me know any comments and suggestions? thanks. Qing > On Feb 3, 2023, at 3:55 PM, Joseph Myers wrote: >=20 > On Thu, 2 Feb 2023, Siddhesh Poyarekar wrote: >=20 >> I dug into this on the glibc end and it looks like this commit: >>=20 >> commit 63fb8f9aa9d19f85599afe4b849b567aefd70a36 >> Author: Zack Weinberg >> Date: Mon Feb 5 14:13:41 2018 -0500 >>=20 >> Post-cleanup 2: minimize _G_config.h. >>=20 >> ripped all of that gunk out. AFAICT there's no use of struct __gconv_in= fo >> anywhere else in the code. >>=20 >> I reckon it is safe to say now that glibc no longer needs this misfeatur= e. >=20 > It would be worth testing whether any change warns anywhere else in glibc= =20 > (not necessarily in installed headers). And to have fixincludes for the= =20 > installed _G_config.h from old glibc if we start rejecting such code. >=20 > --=20 > Joseph S. Myers > joseph@codesourcery.com