lkml.org 
[lkml]   [2022]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v6 2/3] random: introduce generic vDSO getrandom() implementation
    Hi Florian,

    On Wed, Nov 23, 2022 at 11:48:06AM +0100, Florian Weimer wrote:
    > * Jason A. Donenfeld:
    >
    > > static void *vgetrandom_alloc(size_t *num, size_t *size_per_each, unsigned int flags)
    > > {
    > > unsigned long ret = syscall(__NR_vgetrandom_alloc, num, size_per_each, flags);
    > > return ret > -4096UL ? NULL : (void *)ret;
    > > }
    >
    > The traditional syscall function returns -1 on error and set errors, so
    > using unsing long and the 4096 is quite misleading.

    Not sure I have any idea at all whatsoever about what you're talking
    about. Firstly, the function you quoted is from the "sample userspace
    code" in the commit message, so it might not be code for the context you
    have in mind.

    Secondly, it's just doing the thing to figure out if the return value is
    an error value or a pointer. Were we in glibc, we'd write this as:

    return INTERNAL_SYSCALL_ERROR_P(r) ? NULL : (void *) r;

    Right? And if you look at the expansion of that glibc macro, it's just:

    #define INTERNAL_SYSCALL_ERROR_P(val) \
    ((unsigned long int) (val) > -4096UL)

    So it looks like the same exact thing?

    The only difference I could see is that I assign it to a `unsigned long
    ret`, while glibc code tends to assign it to a `long r`? Is that the
    difference you're pointing out? Except that clearly doesn't matter
    because it just gets casted to unsigned by that macro anyway?

    Confused.

    Jason

    \
     
     \ /
      Last update: 2022-11-24 02:10    [W:2.554 / U:0.440 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site