Messages in this thread |  | | | From | "H. Peter Anvin" <> | | Subject | Re: Is the x86-64 kernel size limit real? | | Date | Thu, 22 Jun 2006 14:38:02 -0700 (PDT) |
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Followup to: <20060622204627.GA47994@dspnet.fr.eu.org> By author: Olivier Galibert <galibert@pobox.com> In newsgroup: linux.dev.kernel > > I get bitched at by the build process because the kernel I get is > around 4.5Mb compressed. i386 does not have that limitation. > Interestingly, a diff between the two build.c gives: > > --- ../../../i386/boot/tools/build.c 2006-06-22 20:19:33.000000000 +0200 > +++ build.c 2006-06-22 20:19:33.000000000 +0200 > @@ -70,8 +70,7 @@ > > int main(int argc, char ** argv) > { > - unsigned int i, sz, setup_sectors; > - int c; > + unsigned int i, c, sz, setup_sectors; > u32 sys_size; > byte major_root, minor_root; > struct stat sb; > @@ -150,8 +149,10 @@ > sz = sb.st_size; > fprintf (stderr, "System is %d kB\n", sz/1024); > sys_size = (sz + 15) / 16; > - if (!is_big_kernel && sys_size > DEF_SYSSIZE) > - die("System is too big. Try using bzImage or modules."); > + /* 0x40000*16 = 4.0 MB, reasonable estimate for the current maximum */ > + if (sys_size > (is_big_kernel ? 0x40000 : DEF_SYSSIZE)) > + die("System is too big. Try using %smodules.", > + is_big_kernel ? "" : "bzImage or "); > while (sz > 0) { > int l, n; > > > which shows two things: > 1- a8f5034540195307362d071a8b387226b410469f should have a x86-64 version > 2- the limit looks entirely artificial > > So, is removing the limit prone to bite me? >
It turns out x86-64, unlike i386, does still have a hardcoded limit, but the limit in build.c is wrong:
kernel/head.S: /* 40MB kernel mapping. The kernel code cannot be bigger than that. When you change this change KERNEL_TEXT_SIZE in page.h too. */ /* (2^48-(2*1024*1024*1024)-((2^39)*511)-((2^30)*510)) = 0 */ So this should be replaced by KERNEL_TEXT_SIZE in page.h, or better, this should be done dynamically in x86-64 too.
-hpa
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