Re: [PATCH] Improve execl* functions

Hi Federico,

On Jan 26 12:14, Federico Terraneo wrote:
> Hi,
> I propose the following patch to the execl* functions in newlib that does
> the following:
> - it returns an error if more than the maximum number of arguments are
> passed instead of corrupting the stack
> - it allows to tweak the maximum number of arguments at the time of
> compiling newlib by defining the ARG_NUM_MAX macro
> 
> This patch is originally meant for the Miosix OS to allow reducing the
> maximum number of arguments with the intent of reducing the stack usage of
> the execl* functions in low memory microcontrollers, but I think it is of
> general applicability and can of course be useful also to increase this
> value for desktop-class targets.
> 
> Best regards,
> Federico Terraneo
> 
> 

I'm sorry, but I don't think this is the right thing to do.  Actually,
not even for Miosix OS.  Here's why:

Adding ARG_NUM_MAX this way requires all targets to define their own
ARG_NUM_MAX if they want to support more than 256 args.  Right now,
there's no such limitation.

There already is a standarized way for all targets to tell userspace how
much memory can be used by the exec(3) family of functions:

  ARG_MAX from limits.h or sysconf (_SC_ARG_MAX) from unistd.h

  must be >= _POSIX_ARG_MAX (4096)

ARG_MAX does not define a max number of args.  It defines a max number
of bytes used for arguments and environment combined.  This is what
should be tested for in exec(3), if you want to enforce memory usage
restrictions.


Thanks,
Corinna