[Buildroot] json-c fix, question about -D_REENTRANT

[Buildroot] json-c fix, question about -D_REENTRANT

[Thomas Petazzoni]

Hello,

The attached patch fixes the build of json-c when thread support is
not available. This library does not require thread support: it was
compatible with -D_REENTRANT in all cases, which is only possible when
thread support is available.

However, I didn't commit this directly, because I am not sure what the
right fix is. My fix is to just get rid of -D_REENTRANT.

However, according to
http://pauillac.inria.fr/~xleroy/linuxthreads/faq.html#H, all code
used in a multithreaded application should be built with -D_REENTRANT,
even if this code itself is not creating/manipulating threads.

So, technically, removing -D_REENTRANT seems like an incorrect: it
should be kept if the toolchain supports thread.

However, looking quickly at a number of other libraries, I don't see
any of them being careful about this. I know the -pthread gcc options
passes both the -lpthread linker option and the -D_REENTRANT compiler
option, but I don't see -pthread being used in libraries that don't
need thread support, but that may be used in a multithreaded
application.

Am I missing something?

Thanks,

Thomas

[Buildroot] [PATCH] json-c: fix build when no thread support is available

[Thomas Petazzoni]

Fixes
http://autobuild.buildroot.org/results/1d9a2e44da3aa627265b03763ca324c609c0c61c/build-end.log.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
 package/json-c/json-c-no-reentrant.patch |   33 ++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 package/json-c/json-c-no-reentrant.patch

diff --git a/package/json-c/json-c-no-reentrant.patch b/package/json-c/json-c-no-reentrant.patch
new file mode 100644
index 0000000..a01181c
--- /dev/null
+++ b/package/json-c/json-c-no-reentrant.patch
@@ -0,0 +1,33 @@
+Do not pass -D_REENTRANT
+
+This flag is not needed to build this library, and prevents to build
+it with toolchains that don't have thread support.
+
+Since the Makefile.in change is a one-liner, we also do it in the
+patch to avoid having to autoreconfigure the package.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+
+Index: b/Makefile.am
+===================================================================
+--- a/Makefile.am
++++ b/Makefile.am
+@@ -1,4 +1,4 @@
+-AM_CFLAGS = -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE -D_REENTRANT
++AM_CFLAGS = -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE
+ 
+ EXTRA_DIST = README.html README-WIN32.html config.h.win32 doc
+ 
+Index: b/Makefile.in
+===================================================================
+--- a/Makefile.in
++++ b/Makefile.in
+@@ -219,7 +219,7 @@
+ top_build_prefix = @top_build_prefix@
+ top_builddir = @top_builddir@
+ top_srcdir = @top_srcdir@
+-AM_CFLAGS = -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE -D_REENTRANT
++AM_CFLAGS = -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE
+ EXTRA_DIST = README.html README-WIN32.html config.h.win32 doc
+ lib_LTLIBRARIES = libjson.la
+ pkgconfigdir = $(libdir)/pkgconfig
-- 
1.7.9.5

[Buildroot] json-c fix, question about -D_REENTRANT

[Arnout Vandecappelle]

On 08/25/12 16:13, Thomas Petazzoni wrote:
> The attached patch fixes the build of json-c when thread support is
> not available. This library does not require thread support: it was
> compatible with -D_REENTRANT in all cases, which is only possible when
> thread support is available.
>
> However, I didn't commit this directly, because I am not sure what the
> right fix is. My fix is to just get rid of -D_REENTRANT.
>
> However, according to
> http://pauillac.inria.fr/~xleroy/linuxthreads/faq.html#H, all code
> used in a multithreaded application should be built with -D_REENTRANT,
> even if this code itself is not creating/manipulating threads.

  Note that that FAQ is pretty old.

>
> So, technically, removing -D_REENTRANT seems like an incorrect: it
> should be kept if the toolchain supports thread.

  I looked at the source of uClibc 0.32 and 0.33, and it looks like they
automatically select the reentrant versions of errno and getc if
HAS_THREADS is defined.  As to the _r reentrant functions, they're
always there (except, for some reason, getlogin_r) - but for those you'd
anyway get a compile or link error.

  I expect glibc will always build the reentrant versions.

  So I guess you can remove the -D_REENTRANT.


  Regards,
  Arnout

-- 
Arnout Vandecappelle                               arnout at mind be
Senior Embedded Software Architect                 +32-16-286540
Essensium/Mind                                     http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium                BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
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[Buildroot] [PATCH] json-c: fix build when no thread support is available

[Peter Korsgaard]

>>>>> "Thomas" == Thomas Petazzoni <thomas.petazzoni@free-electrons.com> writes:

 Thomas> Fixes
 Thomas> http://autobuild.buildroot.org/results/1d9a2e44da3aa627265b03763ca324c609c0c61c/build-end.log.

Committed, thanks.

-- 
Bye, Peter Korsgaard