Re: Nmap 7.50 GCC 6 warnings

[Daniel Miller <bonsaiviking () gmail com>]

Victor,

Thanks for the warning. That line has actually changed since the last
release, and no longer has the misleading indentation. The code itself
was correct, so there is no change in functionality. Here is the
commit in question:
https://github.com/nmap/nmap/commit/cb17b788b335d8edc1c6801db3f5492295c82c0f

Dan

On Wed, Jul 5, 2017 at 12:24 PM, Victor Coss via dev <dev () nmap org> wrote:
> Hello, when I compiled Nmap 7.50 on the latest Debian Stretch (9) using GCC
> version, gcc (Debian 6.3.0-18) 6.3.0 20170516, I have noticed the following
> warnings. They were easy to notice as they light up different colors.
>
> make[2]: 'liblua.a' is up to date.
> make[2]: Leaving directory '/opt/nmap-7.50/liblua'
> gcc -I./../liblua  -I../libpcap -DHAVE_CONFIG_H
> -DNCAT_DATADIR="\"/usr/local/share/ncat\"" -D_FORTIFY_SOURCE=2 -I. -I..
> -I../nsock/include/ -I../nbase -DLUA_USE_POSIX -DLUA_USE_DLOPEN -DHAVE_LUA=1
> -I../liblua -g -O2 -Wall -c ncat_main.c -o ncat_main.o
> gcc -I./../liblua  -I../libpcap -DHAVE_CONFIG_H
> -DNCAT_DATADIR="\"/usr/local/share/ncat\"" -D_FORTIFY_SOURCE=2 -I. -I..
> -I../nsock/include/ -I../nbase -DLUA_USE_POSIX -DLUA_USE_DLOPEN -DHAVE_LUA=1
> -I../liblua -g -O2 -Wall -c ncat_connect.c -o ncat_connect.o
> ncat_connect.c: In function ‘read_stdin_handler’:
> ncat_connect.c:1219:7: warning: this ‘if’ clause does not guard...
> [-Wmisleading-indentation]
>        if (!o.noshutdown)
>        ^~
> ncat_connect.c:1222:9: note: ...this statement, but the latter is
> misleadingly indented as if it is guarded by the ‘if’
>          if (o.proto != IPPROTO_TCP || (o.proto == IPPROTO_TCP &&
> o.sendonly))
>          ^~
> gcc -I./../liblua  -I../libpcap -DHAVE_CONFIG_H
> -DNCAT_DATADIR="\"/usr/local/share/ncat\"" -D_FORTIFY_SOURCE=2 -I. -I..
> -I../nsock/include/ -I../nbase -DLUA_USE_POSIX -DLUA_USE_DLOPEN -DHAVE_LUA=1
> -I../liblua -g -O2 -Wall -c ncat_core.c -o ncat_core.o
>
>
> When doing research, it appears this is due to changes with the new GCC 6. I
> found the following information on GCC's site (link to page) about porting
> to GCC 6,
>
>
> -Wmisleading-indentation
>
> A new warning -Wmisleading-indentation was added to -Wall, warning about
> places where the indentation of the code might mislead a human reader about
> the control flow:
>
> sslKeyExchange.c: In function 'SSLVerifySignedServerKeyExchange':
> sslKeyExchange.c:629:3: warning: this 'if' clause does not guard...
> [-Wmisleading-indentation]
>     if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
>     ^~
> sslKeyExchange.c:631:5: note: ...this statement, but the latter is
> misleadingly indented as if it is guarded by the 'if'
>         goto fail;
>         ^~~~
>
> This has highlighted genuine bugs, often due to missing braces, but it
> sometimes reports warnings for poorly-indented files, or on projects with
> unusual indentation. This may cause build errors if you have -Wall -Werror
> in your project.
>
> The best fix is usually to fix the indentation of the code to match the
> block structure, or to fix the block structure by adding missing braces. If
> changing the source is not practical or desirable (e.g. for autogenerated
> code, or to avoid churn in the source history), the warning can be disabled
> by adding -Wno-misleading-indentation to the build flags. Alternatively, you
> can disable it for just one part of a source file or function using pragmas:
>
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wmisleading-indentation"
>
> /* (code for which the warning is to be disabled)  */
>
> #pragma GCC diagnostic pop
>
> Source files with mixed tabs and spaces that don't use 8-space tabs may lead
> to warnings. A real-world example was for such a source file, which
> contained an Emacs directive to view tabs to be 4 spaces wide:
>
>   /* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
> */
>
> The mixture of tabs and spaces did correctly reflect the block structure
> when viewed in Emacs, but not in other editors, or in an HTML view of the
> source repository. By default, -Wmisleading-indentation assumes tabs to be 8
> spaces wide. It would have been possible to avoid this warning by adding
> -ftabstop=4 to the build flags for this file, but given that the code was
> confusing when viewed in other editors, the indentation of the source was
> fixed instead.
>
>
>
> _______________________________________________
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