Re: [uclibc-ng-devel] stdio fudging errno ?

From: Florian Weimer <fw@deneb.enyo.de>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: "devel@uclibc-ng.org" <devel@uclibc-ng.org>,
	"jan.vangorp_ext@softathome.com" <jan.vangorp_ext@softathome.com>,
	arcml <linux-snps-arc@lists.infradead.org>
Subject: Re: [uclibc-ng-devel] stdio fudging errno ?
Date: Sat, 14 Dec 2019 10:37:08 +0100	[thread overview]
Message-ID: <87k16zdz97.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <77f8a379-f3dc-6d15-4d8a-20be0346e9f6@synopsys.com> (Vineet Gupta's message of "Thu, 12 Dec 2019 23:54:36 +0000")

* Vineet Gupta:

> Here's a simple test case which shows the problem:
>
> 	#define _GNU_SOURCE
> 	#include <stdio.h>
> 	#include <stdlib.h>
> 	#include <errno.h>
>
> 	void main(void)
> 	{
>         	const char *this_func = "finite";
> 	        char *test_name;
>
>         	errno = 0;
> 	        if (asprintf (&test_name, "%s (%s)", this_func, "my-str") == -1)
> 			abort ();
>
> 	        printf("%d\n", errno);	// <-- prints 11
> 	}
>
> The errno unconditionally being set to EAGAIN seems to have been
> introduced in commit 568ceebf6adfc58c64a95133311268db6 ("Fix
> infinite loop when fopencookie custom write returns 0 on error")
> bakc in 2016.

For functions specified by standards, successful calls can alter errno
unless specified otherwise.  asprintf is not a standardized function,
but it is reasonable to expect that a similar rule applies.

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