[PATCH] fix sysconf(_SC_LINE_MAX) to return LINE_MAX

[PATCH] fix sysconf(_SC_LINE_MAX) to return LINE_MAX

[Christian Wiese]

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Hi,

attached is a patch for fixing sysconf(_SC_LINE_MAX) to not always
return -1 but LINE_MAX as defined in limits.h.

Greetings
Chris

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From 9f7717649e338e53e8d068e8722f03229d1dd99b Mon Sep 17 00:00:00 2001
From: Christian Wiese <chris@opensde.org>
Date: Wed, 7 May 2014 10:43:28 +0200
Subject: [PATCH] fix sysconf(_SC_LINE_MAX) to return LINE_MAX

The problem was discovered when calling the wall(1) command from util-linux

---------------------------------------------------------------------------
./wall "123"
wall: cannot allocate 18446744073709551615 bytes: Out of memory
---------------------------------------------------------------------------

triggered by 'makemsg()' in 'term-utils/wall.c' which uses sysconf() to
determine LINE_MAX for allocating a buffer through the builtin xmalloc()

---------------%<----------------------------------------------------------
char *p, *lbuf, *tmpname, *mbuf;
long line_max;

line_max = sysconf(_SC_LINE_MAX);
lbuf = xmalloc(line_max);
---------------%<----------------------------------------------------------

which fails because in musl sysconf(_SC_LINE_MAX) is always returning -1.

Signed-off-by: Christian Wiese <chris@opensde.org>
---
 src/conf/sysconf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/conf/sysconf.c b/src/conf/sysconf.c
index bf433d6..21e0743 100644
--- a/src/conf/sysconf.c
+++ b/src/conf/sysconf.c
@@ -66,7 +66,7 @@ long sysconf(int name)
 		[_SC_COLL_WEIGHTS_MAX] = COLL_WEIGHTS_MAX,
 		[_SC_EQUIV_CLASS_MAX] = -1, /* ?? */
 		[_SC_EXPR_NEST_MAX] = -1,
-		[_SC_LINE_MAX] = -1,
+		[_SC_LINE_MAX] = LINE_MAX,
 		[_SC_RE_DUP_MAX] = RE_DUP_MAX,
 		[_SC_CHARCLASS_NAME_MAX] = -1, /* ?? */
 		[_SC_2_VERSION] = VER,
-- 
1.9.1


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Re: [PATCH] fix sysconf(_SC_LINE_MAX) to return LINE_MAX

[Rich Felker]

On Wed, May 07, 2014 at 11:26:39AM +0200, Christian Wiese wrote:
> Hi,
> 
> attached is a patch for fixing sysconf(_SC_LINE_MAX) to not always
> return -1 but LINE_MAX as defined in limits.h.

I've been looking into this, but -1 seems to be the correct way for
the implementation to report that it does not impose an arbitrary
limit. The specification of limits.h calls for these macros to be
defined with "minimum maximum" values (the lowest limit the
implementation might impose) while sysconf may return a more-relaxed
value. It's not 100% clear whether it's intended that sysconf return
-1 for them, but it seems valid and reasonable. I'd like to hear other
opinions on the matter.

Rich