Bug#839101: cowdancer: Keep open() async-signal-safe

[Thorsten Glaser]

Jack Bates dixit:

>A) Call dlsym() early, before anything calls open(). Not possible
>   because even if you managed to call dlsym() before anything else,
>   dlsym() itself might call open() before it was done initializing :-(
>
>B) Avoid dlsym() altogether. What are the options in this case?
>
>   1) Use sys_open() instead of dlsym(RTLD_NEXT, "open)

How about a combination of both?

Something like this (pseudo code, mostly):


static void initialise_open(void) __attribute__((__constructor__));

static uint8_t open_initialised = 0;

int
open(const char *path, int flags, mode_t mode)
{
	if (!open_initialised)
		return (sys_open(path, flags, mode));
	/* current code with dlsym’s result */
}

static void
initialise_open(void)
{
	/* call dlsym, which is now allowed to call open() */
	/* store its result */
	open_initialised = 1;
}


Of course, I probably ought to better go to bed, but someone
might make something off this. Also, completely untested, modulo
that I have an application in which these constructors work, in
plain GCC (no C++).

Good night,
//mirabilos
-- 
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