From: "Ahmed S. Darwish" <darwish.07@gmail.com> To: linux-kernel@vger.kernel.org Subject: [i386] Questions regarding provisional page tables initialization Date: Sun, 1 Jul 2007 23:38:33 +0300 Message-ID: <20070701203833.GA3498@Ahmed> (raw) Hi list, AFAIK, in the initializaion phase, kernel builds pages tables with two mappings, identity and PAGE_OFFSET + C mapping. The provisional _global directory_ is contained in swapper_pg_dir variable. while the provisional _page tables_ are stored starting from pg0, right after _end. There're some stuff that confused me for a full day about the code (head.S) that accomplishes the above words: movl $(pg0 - __PAGE_OFFSET), %edi movl $(swapper_pg_dir - __PAGE_OFFSET), %edx movl $0x007, %eax /* 0x007 = PRESENT+RW+USER */ 10: leal $0x007(%edi),%ecx /* Create PDE entry */ What does the address of 7 bytes displacement after %edi - the physical address of pg0 - represent ?. Why not just putting the address of %edi (the address of pagetable cell to be mapped by swapper_pg_dir) in %ecx without displacement? page_pde_offset = (__PAGE_OFFSET >> 20) movl %ecx,(%edx) /* Store identity PDE entry */ movl %ecx,page_pde_offset(%edx) /* Store kernel PDE entry */ Why the pde_offset is PAGE_OFFSET >> 20 instead of PAGE_OFFSET >> 22 ? * 22 to right shift the whole page_shift (12) and pgdir_shift (10) bits. [...] /* Initialize the 1024 _page table_ cells with %eax (0x007) */ movl $1024, %ecx 11: stosl addl $0x1000,%eax loop 11b The page table entries beginning from pg0 (pointed by %edi) and following pages are initialized with the series 7 + 8 + 8 + ... for each cell. This series has the property of setting the PRESENT+RW+USER bits in the whole entries to 1 but it sets lots of the entries BASE address to 0 too. Why is this done ? Thanks, -- Ahmed S. Darwish HomePage: http://darwish.07.googlepages.com Blog: http://darwish-07.blogspot.com
next reply index Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2007-07-01 20:38 Ahmed S. Darwish [this message] 2007-07-01 22:02 ` Andreas Schwab 2007-07-01 22:19 ` Jeremy Fitzhardinge 2007-07-02 1:13 ` Ahmed S. Darwish 2007-07-02 9:18 ` Andreas Schwab 2007-07-02 10:23 ` Ahmed S. Darwish 2007-07-02 11:34 ` Brian Gerst 2007-07-02 15:43 ` Ahmed S. Darwish 2007-07-02 10:43 ` Andi Kleen
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20070701203833.GA3498@Ahmed \ --to=darwish.07@gmail.com \ --cc=linux-kernel@vger.kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
LKML Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lkml.kernel.org/lkml/0 lkml/git/0.git git clone --mirror https://lkml.kernel.org/lkml/1 lkml/git/1.git git clone --mirror https://lkml.kernel.org/lkml/2 lkml/git/2.git git clone --mirror https://lkml.kernel.org/lkml/3 lkml/git/3.git git clone --mirror https://lkml.kernel.org/lkml/4 lkml/git/4.git git clone --mirror https://lkml.kernel.org/lkml/5 lkml/git/5.git git clone --mirror https://lkml.kernel.org/lkml/6 lkml/git/6.git git clone --mirror https://lkml.kernel.org/lkml/7 lkml/git/7.git git clone --mirror https://lkml.kernel.org/lkml/8 lkml/git/8.git git clone --mirror https://lkml.kernel.org/lkml/9 lkml/git/9.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 lkml lkml/ https://lkml.kernel.org/lkml \ linux-kernel@vger.kernel.org public-inbox-index lkml Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel AGPL code for this site: git clone https://public-inbox.org/public-inbox.git