Rich,

Thank you for the extremely informative and quick response! I suspect in the small, understandable places that use this function in this package it should be possible to avoid multiple evaluations (well, at least for this version of the code; no g'tee that would hold).

Out of interest, I presume there's no guarantee that alloca is aligned? It's not a feature I've ever used - it seems like a micro-optimisation for tight loops that should be made as part of a decision by a higher-level language (eg Vala, which, as I understand, doesn't).

BTW, This package has a few more issues than just musl ones... it doesn't understand cross-compilation for starters, makes insane use of code generation (always a big smell in my book, especially when done using a compiled language). Looks like it suffers from not enough peer review / usage...

Raphael Cohn
Chief Architect, stormmq
Co-Chair, OASIS MQTT Standard
Secretary, OASIS AMQP Standard
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On 1 January 2014 19:54, Rich Felker <dalias@aerifal.cx> wrote:
On Wed, Jan 01, 2014 at 07:42:47PM +0000, Raphael Cohn wrote:
> Hi,
>
> I'm trying to compile 'audit' (aka libaudit, auditd, etc - from
> http://people.redhat.com/sgrubb/audit/index.html version 2.3.2). Using musl
> 0.9.14.
>
> The file 'src/ausearch-lol.c' uses a reference to 'strndupa', which I
> presume is an alloca version of strndup, and presumably a _GNU_SOURCE
> feature. I can't seem to see a definition for it in musl, although strdupa
> exists in string.h (Indeed, http://linux.die.net/man/3/strdup suggests as
> much).
>
> Is this intentional? If so, what would anyone suggest as a work around? My
> guess would be  #define strndupa(x, t) strncpy(alloca(strlen(x)+1),x,t)
> but I'd like a second opinion...

That's roughly the way to do it, but you need strnlen, not strlen, and
there are various other details like properly parenthesizing macro
arguments. In addition, there's no way to avoid multiple-evaluations
of arguments unless you use the GNU C statement-expressions extension.

It should be noted that almost any use of alloca is either a bug
(potentially exploitable stack overflow) or useless (because the size
is bounded and thus could/should just be replaced by a fixed-size
array). This is the main reason I've been hesitant to go to the
trouble of providing this and dealing with the multiple-evaluation or
#ifdef __GNUC__ issue -- really, any software using alloca (and by
extension, strdupa or strndupa) should be fixed.

Rich