Bug#162576: marked as done (libc6-dev: errno is a function call in non-threaded program)
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From: <herbert@gondor.apana.org.au>
Subject: libc6-dev: errno is a function call in non-threaded program
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Date: Fri, 27 Sep 2002 20:55:30 +1000
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Package: libc6-dev
Version: 2.2.5-14.3
Severity: minor
bits/errno.h defines errno to be a function call even when the application
has no need for threads at all. This definition should be made conditional
so that non-threaded programs do not suffer the overhead of the function
call.
-- System Information
Debian Release: testing/unstable
Kernel Version: Linux gondolin 2.4.18-686-smp #1 SMP Sun Apr 14 12:07:19 EST 2002 i686 unknown unknown GNU/Linux
Versions of the packages libc6-dev depends on:
ii libc6 2.2.5-14.3 GNU C Library: Shared libraries and Timezone
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Date: Fri, 27 Sep 2002 10:12:09 -0400
From: Ben Collins <bcollins@debian.org>
To: herbert@gondor.apana.org.au, 162576-done@bugs.debian.org
Subject: Re: Bug#162576: libc6-dev: errno is a function call in non-threaded program
Message-ID: <20020927141209.GK564@phunnypharm.org>
References: <[🔎] E17usmQ-0008Vz-00@gondolin.me.apana.org.au>
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On Fri, Sep 27, 2002 at 08:55:30PM +1000, herbert@gondor.apana.org.au wrote:
> Package: libc6-dev
> Version: 2.2.5-14.3
> Severity: minor
>
> bits/errno.h defines errno to be a function call even when the application
> has no need for threads at all. This definition should be made conditional
> so that non-threaded programs do not suffer the overhead of the function
> call.
How do you figure?
# ifndef __ASSEMBLER__
/* We now need a declaration of the `errno' variable. */
extern int errno;
/* Function to get address of global `errno' variable. */
extern int *__errno_location (void) __THROW __attribute__ ((__const__));
# if defined _LIBC
/* We wouldn't need a special macro anymore but it is history. */
# define __set_errno(val) (*__errno_location ()) = (val)
# endif /* _LIBC */
# if !defined _LIBC || defined _LIBC_REENTRANT
/* When using threads, errno is a per-thread value. */
# define errno (*__errno_location ())
# endif
# endif /* !__ASSEMBLER__ */
Clearly it only gets defined as (*__errno_location ()) if we are not
_LIBC (not the case for us ever) or _LIBC_REENTRANT is defined.
Now, -D_REENTRANT does not assume threads, but it does assume thread
safe, so the definition is perfectly normal in that case (e.g. a module
or library that does not use threads, being usable by a threaded program
should use this). I don't think this is a bug at all.
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