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Codechange: Use access __attribute__ to silence warnings in GCC #8522

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merged 1 commit into from Jan 8, 2021
Merged

Codechange: Use access __attribute__ to silence warnings in GCC #8522

merged 1 commit into from Jan 8, 2021

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Milek7
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@Milek7 Milek7 commented Jan 8, 2021

Motivation / Problem

GCC in some cases warns about uninitialized uses where in fact pointer is not dereferenced at all, such as last pointer in safe string functions.

/home/milek7/OpenTTD/src/network/network_content_gui.cpp: In member function ‘void NetworkContentListWindow::OpenExternalSearch()’:
/home/milek7/OpenTTD/src/network/network_content_gui.cpp:328:36: warning: ‘last’ may be used uninitialized [-Wmaybe-uninitialized]
  328 |                 char *pos = strecpy(url, "http://grfsearch.openttd.org/?", last);
      |                             ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/milek7/OpenTTD/src/network/core/address.h:15,
                 from /home/milek7/OpenTTD/src/network/core/tcp.h:15,
                 from /home/milek7/OpenTTD/src/network/core/tcp_content.h:16,
                 from /home/milek7/OpenTTD/src/network/network_content.h:13,
                 from /home/milek7/OpenTTD/src/network/network_content_gui.h:13,
                 from /home/milek7/OpenTTD/src/network/network_content_gui.cpp:23:
/home/milek7/OpenTTD/src/network/core/../../string_func.h:34:7: note: by argument 3 of type ‘const char*’ to ‘char* strecpy(char*, const char*, const char*)’ declared here
   34 | char *strecpy(char *dst, const char *src, const char *last);
      |       ^~~~~~~
/home/milek7/OpenTTD/src/network/network_content_gui.cpp:325:22: note: ‘url’ declared here
  325 |                 char url[1024];
      |                      ^~~

Description

Add NOACCESS macro that uses access __attribute__ to tell compiler that pointer is not dereferenced at all. https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

Limitations

None (except ugly macro).

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

  • The bug fix is important enough to be backported? (label: 'backport requested')
  • This PR affects the save game format? (label 'savegame upgrade')
  • This PR affects the GS/AI API? (label 'needs review: Script API')
    • ai_changelog.hpp, gs_changelog.hpp need updating.
    • The compatibility wrappers (compat_*.nut) need updating.
  • This PR affects the NewGRF API? (label 'needs review: NewGRF')

@LordAro
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LordAro commented Jan 8, 2021

While I don't doubt this is fine, where are you seeing these GCC warnings? I've not seen anything like them before

@Milek7
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Milek7 commented Jan 8, 2021 

gcc --version
gcc (GCC) 11.0.0 20200910 (experimental)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

@LordAro
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LordAro commented Jan 8, 2021

Ah, shiny new GCC 11 warnings

@LordAro LordAro merged commit 639cfa4 into OpenTTD:master Jan 8, 2021
@glx22 glx22 mentioned this pull request Jan 8, 2021
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@LordAro LordAro mentioned this pull request Apr 27, 2021
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@LordAro LordAro LordAro approved these changes

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@Milek7 @LordAro