Date: Sun, 2 Dec 2012 08:39:53 +0000 From: Justin Cormack <justin@...cialbusservice.com> To: musl@...ts.openwall.com Subject: Re: some issues with #defines On 2 Dec 2012 03:26, "Rich Felker" <dalias@...ifal.cx> wrote: > > On Sat, Dec 01, 2012 at 11:52:19PM +0000, Justin Cormack wrote: > > PAGE_SIZE is defined in include/bits/limits.h but I am not sure it should > > be. As far as I can see glibc does not define it at all any more fo > > userspace (see man page for getpagesize). > > I'm aware that glibc does not define it because they consider it > variable. musl considers it constant because increasing it just wastes > large amounts of memory. The OS is still free to use larger hardware > pages transparently when possible; all PAGE_SIZE really represents the > the granularity of mmap. > > I've only run into one program which had a problem due to musl > defining PAGE_SIZE; it was using PAGE_SIZE for its own purposes. This > usage is non-portable since POSIX defines PAGE_SIZE. Per POSIX, if > PAGE_SIZE is defined it's a contant, and if it's not defined, it might > be variable, and the application must use sysconf() to query the page > size. Portable applications can always use sysconf() if desired, but > portable applications wanting to be more efficient can conditionally > use PAGE_SIZE directly if it's defined (allowing a lot of compile-time > constant propagation optimizations) and only fallback to the slower > and more bloated runtime calculations on systems that lack the macro. Thanks for that. It is including it because it is also including kernel headers which is always a mess. > > Running into other issues too with includes but suspect they are include > > bugs and need to look at them further, was looking at compiling native kvm > > tool. > > There are still lots of issues with very-low-level programs that do > hackish trace/debugger/jit type stuff not liking musl's headers. I'm > working on improving the situation in some respects, but I'm not sure > how successful things will be without some help from their side too. > Yes it is basically defining userspace kernel drivers so liable to be messy. However it only seems to be a few places so will have a look at patching it. It gives a way to run KVM without qemu and with much less code (5k lines) so would be nice to have. Justin Content of type "text/html" skipped
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