[9fans] ARG_MAX of Plan9

[9fans] ARG_MAX of Plan9

[arisawa]

Hello 9fans,

I have a question: what is the value of ARG_MAX of Plan9?

In Mac/OSX, the value is defined in /usr/include/sys/syslimits.h:
#define	ARG_MAX		   (256 * 1024)    /* max bytes for an exec function */

In APE, we can find the value in Plan9 source.
/sys/include/ape/sys/limits.h:
#define	ARG_MAX		16384

However, I couldn't find ARG_MAX of Plan9.

Kenji Arisawa

Re: [9fans] ARG_MAX of Plan9

[Charles Forsyth]

[-- Attachment #1: Type: text/plain, Size: 510 bytes --]

It's limited by the size of the temporary stack during exec, and
platform-specific.
The smallest seems to be 100 4k pages (less space for argv and Tos, I
suppose).
Newer variants of the system raise that to the size of the stack segment
(eg, 16 Mbytes),
which is still platform-specific. In fact, glancing at sysproc.c, I'm not
sure why it's limited
to TSTKSIZ given it goes on to allocate a much bigger segment to put them
in,
but even if that could easily be removed, currently that is the limit.

[-- Attachment #2: Type: text/html, Size: 585 bytes --]

Re: [9fans] ARG_MAX of Plan9

[cinap_lenrek]

as far as i can see, its just limited by this:
    /*
	 * Build the stack segment, putting it in kernel virtual for the moment
	 */
	if(spage > TSTKSIZ)
		error(Enovmem);

in pc/mem.h:55: #define	TSTKSIZ 	100			/* pages in new stack; limits exec args */

so that will give you arround half a megabyte for program
arguments.

--
cinap