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https://issues.apache.org/jira/browse/HADOOP-11997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14561281#comment-14561281
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Allen Wittenauer commented on HADOOP-11997:
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bq. However the -D_GNU_SOURCE flag is toxic to portability and will just
repeatedly cause portability breakage if it's left in so I'm intending to
remove it and explicitly bracket all such Linux-specific code in the source
with #define/#undef blocks. That will mean that people doing port work to other
platforms will have an easier time of it in future.
+1 to this approach. It's been a huge problem over the years to have all of
these wacky Linux-only functions hanging around in random places, especially
when there is a perfectly fine POSIX equivalent.
> CMake CMAKE_C_FLAGS are non-portable
> ------------------------------------
>
> Key: HADOOP-11997
> URL: https://issues.apache.org/jira/browse/HADOOP-11997
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: build
> Affects Versions: 2.7.0
> Environment: All
> Reporter: Alan Burlison
> Assignee: Alan Burlison
> Priority: Critical
>
> hadoop-common-project/hadoop-common/src/CMakeLists.txt
> (https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/CMakeLists.txt#L110)
> contains the following unconditional assignments to CMAKE_C_FLAGS:
> set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -g -Wall -O2")
> set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_REENTRANT -D_GNU_SOURCE")
> set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_LARGEFILE_SOURCE
> -D_FILE_OFFSET_BITS=64")
> There are several issues here:
> 1. "-D_GNU_SOURCE" globally enables the use of all Linux-only extensions in
> hadoop-common native source. This is probably a major contributor to the poor
> cross-platform portability of Hadoop native code to non-Linux platforms as it
> makes it easy for developers to use non-portable Linux features without
> realising. Use of Linux-specific features should be correctly bracketed with
> conditional macro blocks that provide an alternative for non-Linux platforms.
> 2. "-g -Wall -O2" turns on debugging for all builds, I believe the correct
> mechanism is to set the CMAKE_BUILD_TYPE CMake variable. If it is still
> necessary to override CFLAGS it should probably be done conditionally
> dependent on the value of CMAKE_BUILD_TYPE.
> 3. "-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" On Solaris these flags are
> only needed for largefile support in ILP32 applications, LP64 applications
> are largefile by default. I believe the same is true on Linux, so these flags
> are harmless but redundant for 64-bit compilation.
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