Hi all - I have some questions; I hope they have not already been posed!
- I'm running a bare qemu + pistachio 0.4, and its kickstart + sigma0, with a little root server of my own, on a IA32 architecture. I ask for bootinfo location, and I find it's 0x1000 (that's where kickstart puts it, so it's ok). However, when I try accessing it, I obviously pagefault, but sigma0 refuses to give me that page. Anyway, if I _force_ it it to do (I've tweaked by hand source code), everything works fine - in fact the bootinfo is there, and it is correct. Did I get something wrong?
- Little note: looking kickstart, I found this, around user/util/kickstart/mbi-loader.cc:486:
if (use_bootinfo) { // Allocate and initialize a bootinfo structure. bi = init_bootinfo (&kip); rec = (L4_BootRec_t *) ((L4_Word_t) bi + bi->size);
if (bi) // Record MBI modules rec = record_bootinfo_modules (bi, rec); else use_bootinfo = false; }
(I'm referring to CVS version, If I remember well 0.4 version was exactly the same). The "rec = stuff" isn't wrong? If "bi" is set to NULL by the init_bootinfo (in case of OOM, if I remember well), this segfaults - well, don't know what it does exactly, since there's still no kernel around, and I don't remember IA32 defaults ;D
- Looking L4 specs (even the latest - by the way, how come the sources theirselves aren't published? I would have found it useful when I did those searches about sigma0 ;D), I have found no satisfying explanation about the kinds of memory descriptors L4 knows about. That is, UndefinedMemoryType, BootLoaderSpecificMemoryType, ArchitectureSpecificMemoryType are obvious, but what are the differences between ConventionalMemoryType and SharedMemoryType? What between ReservedMemoryType and DedicatedMemoryType? What are their exact meanings? Not that I absolutely need to work this out now, but I would like to know this better! :-)
- Last: what purpose sigma1 has? I remember reading something about it in the papers about transparent checkouts of kernel state, and stuff like that...
Thank you all for the attention! :-)
Hi, I'm a L4 newbie but I will try to answer some questions.
On Mon, 08 Nov 2004 22:56:02 +0100, Mattia Belletti mattia.belletti@poste.it wrote:
Hi all - I have some questions; I hope they have not already been posed!
- I'm running a bare qemu + pistachio 0.4, and its kickstart + sigma0,
with a little root server of my own, on a IA32 architecture. I ask for bootinfo location, and I find it's 0x1000 (that's where kickstart puts it, so it's ok). However, when I try accessing it, I obviously pagefault, but sigma0 refuses to give me that page. Anyway, if I _force_
Actually this was my problem several days ago :) The reason is that sigma0(at least the one in pistachio 0.4 source tree) tries to find a free page only in conventional memory when handling a page fault. So you should send sigma0 a Sigma0 RPC message that requests the bootinfo location to be mapped to your address space before accessing the location so that a page fault will not occur.
it it to do (I've tweaked by hand source code), everything works fine - in fact the bootinfo is there, and it is correct. Did I get something wrong?
- Little note: looking kickstart, I found this, around
user/util/kickstart/mbi-loader.cc:486:
if (use_bootinfo) { // Allocate and initialize a bootinfo structure. bi = init_bootinfo (&kip); rec = (L4_BootRec_t *) ((L4_Word_t) bi + bi->size); if (bi) // Record MBI modules rec = record_bootinfo_modules (bi, rec); else use_bootinfo = false; }(I'm referring to CVS version, If I remember well 0.4 version was exactly the same). The "rec = stuff" isn't wrong? If "bi" is set to NULL by the init_bootinfo (in case of OOM, if I remember well), this segfaults - well, don't know what it does exactly, since there's still no kernel around, and I don't remember IA32 defaults ;D
umm..I agree on this point. Any L4 kernel hackers, please let us know.
- Looking L4 specs (even the latest - by the way, how come the sources
theirselves aren't published? I would have found it useful when I did those searches about sigma0 ;D), I have found no satisfying explanation about the kinds of memory descriptors L4 knows about. That is, UndefinedMemoryType, BootLoaderSpecificMemoryType, ArchitectureSpecificMemoryType are obvious, but what are the differences between ConventionalMemoryType and SharedMemoryType? What between ReservedMemoryType and DedicatedMemoryType? What are their exact meanings? Not that I absolutely need to work this out now, but I would like to know this better! :-)
I can be wrong here but, Conventional memory is "normal" memory so sigma0 maps/grants a page of conventional memory type only once. Shared memory is the type of memory which any thread can map into its address space. For example, the address range for video(0xa0000~0xbffff) is of shared memory type. Furthermore, because the first memory descriptor usually specifies the entire address space(0x0~0xffffffff) as shared memory type, the memory which doesn't belong to any other types is of shared memory type. I think this type of memory is for device drivers which access some IO addresses. Reserved memory is the memory that the kernel reserves for its own use. I don't know what dedicated memory is.
- Last: what purpose sigma1 has? I remember reading something about it
in the papers about transparent checkouts of kernel state, and stuff like that...
Thank you all for the attention! :-)
-- Mat/tia Belletti - Undergraduate student @ cs.unibo.it ICQ: 33292311 - email: mbellett@cs.unibo.it IRC: RedGlow - site(s): http://mbellett.web.cs.unibo.it/ Jabber: RedGlow - Linux registered user 299762 @ machine 213003
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[Mattia Belletti]
Hi all - I have some questions; I hope they have not already been posed!
- I'm running a bare qemu + pistachio 0.4, and its kickstart +
sigma0, with a little root server of my own, on a IA32 architecture. I ask for bootinfo location, and I find it's 0x1000 (that's where kickstart puts it, so it's ok). However, when I try accessing it, I obviously pagefault, but sigma0 refuses to give me that page. Anyway, if I _force_ it it to do (I've tweaked by hand source code), everything works fine - in fact the bootinfo is there, and it is correct. Did I get something wrong?
When sigma0 sees that some memory is bootloader specific, architecture specific, etc., it assumes that there is some special semantics or contents within this memory. Such memory must be requested specifically using, e.g., L4_Sigma0_GetPage().
- Little note: looking kickstart, I found this, around
user/util/kickstart/mbi-loader.cc:486:
if (use_bootinfo) { // Allocate and initialize a bootinfo structure. bi = init_bootinfo (&kip); rec = (L4_BootRec_t *) ((L4_Word_t) bi + bi->size);
if (bi) // Record MBI modules rec = record_bootinfo_modules (bi, rec); else use_bootinfo = false; }
(I'm referring to CVS version, If I remember well 0.4 version was exactly the same). The "rec = stuff" isn't wrong? If "bi" is set to NULL by the init_bootinfo (in case of OOM, if I remember well), this segfaults - well, don't know what it does exactly, since there's still no kernel around, and I don't remember IA32 defaults ;D
No, it's not entirely wrong. If bi == NULL then you simply set use_bootinfo to false. You also de-reference the NULL pointer, but that's all fine since we're running on physical memory (i.e., no page faults). Of course, this assumes that the null page is actually present in the system---which might be a bad thing to assume. ;-)
- Looking L4 specs (even the latest - by the way, how come the sources
theirselves aren't published? I would have found it useful when I did those searches about sigma0 ;D), I have found no satisfying explanation about the kinds of memory descriptors L4 knows about. That is, UndefinedMemoryType, BootLoaderSpecificMemoryType, ArchitectureSpecificMemoryType are obvious, but what are the differences between ConventionalMemoryType and SharedMemoryType? What between ReservedMemoryType and DedicatedMemoryType? What are their exact meanings? Not that I absolutely need to work this out now, but I would like to know this better! :-)
ConventionalMemoryType - Regular memory
SharedMemoryType - Memory that is available to all users (i.e., everyone can request it from sigma0). This is sometimes used for, e.g., the screen memory (but only for debugging purposes, never in a production system).
ReservedMemoryType - Reserved by kernel.
DedicatedMemoryType - Not avaialble to user (indicates that it is not used by kernel either). This could for example be BIOS specific memory.
- Last: what purpose sigma1 has? I remember reading something about it
in the papers about transparent checkouts of kernel state, and stuff like that...
Yes. Sigma1 could act as a pager for the kernel. This is not currently implemented, though.
eSk
Well, thank you all for the replies, I've cleared my mind a bit ;)
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