Re: struct nbd_reply not packed = trouble?
在 2013-1-11，0:42，Yann Droneaud ydrone...@opteya.com 写道：
Hello kernel hackers,
I noticed that in [linux]/include/uapi/linux/nbd.h the structure
struct nbd_request {
__be32 magic;
__be32 type;/* == READ || == WRITE */
char handle[8];
__be64 from;
__be32 len;
} __attribute__((packed));
is packed
Given a target where ABI requires types to be aligned on their size (1 =
1, 2 = 2, 4 = 4, 8 = 8, etc.)
4 + 4 + 8 + 8 + 4 = 28 bytes
To satisfy __be64 alignement (the strictest), it must be aligned on a 8
bytes boundary, but 28 is not multiple of 8. 32 is. Padding is required.
[The padding is required so that in a array of struct nbd_request[],
all members of all structures are aligned to their requirement alignement]
but its reply counter part
struct nbd_reply {
__be32 magic;
__be32 error;/* 0 = ok, else error */
char handle[8]; /* handle you got from request */
};
4 + 4 + 8 = 16 bytes.
To satisfy __be32 alignement (the strictest), it must be aligned on a 4
bytes boundary and 16 is a multiple of 4: no need for padding.
is not. Since Linux seems to read sizeof(nbd_reply) bytes from the
network (see [1]), the number of bytes read varies with the number of
bytes of the structure.
It won't.
So my understanding is that if the size of struct nbd_reply varies from
platform/compiler to another that means trouble. I wonder:
- Is there anything about struct nbd_reply that would keep its size
equal everywhere or a reason why variance in size is no problem here?
- Any ideas for a platform where you would expect struct nbd_reply to
be other than 4 + 4 + 8 = 16 bytes in size?
Look for an ABI that require 'char' with either property:
- size 1 byte
- alignment 8 (16 bytes !)
Do you mean this structure size will vary on different platform? If yes,
why Linux does not packed here? Thanks
Regards.
--
Yann Droneaud
OPTEYA
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Re: What is asmlinkage ?
在 2013-1-11，11:16，Peter Teoh htmldevelo...@gmail.com 写道： asmlinkage is defined for almost all arch: grep asmlinkage arch/arm/*/* and u got the answer. It seemed that: http://kernelnewbies.org/FAQ/asmlinkage gave the impression that asmlinkage is only for system call, or associated with it. Not really, nothing to do with system call actually. Even though majority (or ALL) of syscall are defined with asmlinkage, but there are many that are not, eg, in arch/arm subdirectory: kernel/irq.c:asmlinkage void __exception_irq_entry kernel/process.c:asmlinkage void ret_from_fork(void) __asm__(ret_from_fork); kernel/smp.c:asmlinkage void __cpuinit secondary_start_kernel(void) kernel/smp.c:asmlinkage void __exception_irq_entry do_IPI(int ipinr, struct pt_regs *regs) just a few examples. Essentially, it is just declared so that the name, for example, do_IPI can be called from assembly, for example in the following pair (arch/arm assumed): /kernel/smp.c: asmlinkage void __exception_irq_entry do_IPI(int ipinr, struct pt_regs *regs) ./include/asm/entry-macro-multi.S: bne do_IPI More info: http://stackoverflow.com/questions/10060168/is-asmlinkage-required-for-a-c-function-to-be-called-from-assembly From above, asmlinkage is also NOT the only way.. The link you provided is obviously specific for X86, rather than ARM. Rajat mentioned that there is no definition of linkage in arch/arm. This should be true. And as I know, arm use register r7 to pass system call number, and use register r0~r3 to pass parameters. This is used by Google when they implement system call in Android. And for calling C function from assembly code is also platform specific, in ARM, it has fixed standard ABI which defines the details about how assembly code calls C function, you can never ask GCC to compile C function by passing parameters on stack and then assume this function can be called from assembly code which is implemented by other developers who obeys standard ARM ABI. On Fri, Jan 4, 2013 at 6:29 PM, anish singh anish198519851...@gmail.com wrote: On Fri, Jan 4, 2013 at 3:41 PM, Rajat Sharma fs.ra...@gmail.com wrote: Is this correct for all architectures? I guess not, asmlinkage is undefined for arm, so I assume this mechanism is not there for arm. then how do they do it? On Fri, Jan 4, 2013 at 2:24 PM, 卜弋天 bu...@live.cn wrote: 在 2013-1-4，15:38，Rajat Sharma fs.ra...@gmail.com 写道： So with asmlinkage we request compiler to put args on stack. What is advantage of this to start_kernel or in general to other functions ? See its about implementation ease and little of performance too. Assuming the default model of keeping arguments in registers is used. lets say arguments are assumed to be in registers R1, R2, R3, R4, R5, R6 and beyond that in stack. Since system call number is a transparent argument which is chopped off when calling the actual kernel handler and if R1 had the system call number, then you have to shift all register values and stack arguments too. Is this correct for all architectures? As I remembered, ARM uses SWI instruction to implement the system call, it will pass system call number by register R7, and use normal register R0~R3 to pass parameters. Now consider that all arguments are pushed on stack (as enforced by asmlinkage), you have all function argument in the beginning of the stack and the system call number on top of the stack. you just need to pop out stack top to remove system call number from function argument. You might argue that why not always keep system call number on stack top and use registers for function arguments? But thats part of the compiler ABI and if you had fewer arguments lets say 2 only and used up R1 and R2 only, you may not jump to stack top directly for storing system call as its turn for R3 as argument. So, isn't it simpler implementation with everything on stack? -Rajat On Fri, Jan 4, 2013 at 12:13 PM, Rahul Bedarkar rpal...@gmail.com wrote: Thanks. So with asmlinkage we request compiler to put args on stack. What is advantage of this to start_kernel or in general to other functions ? Regards, Rahul On Thu, Jan 3, 2013 at 9:34 PM, Mulyadi Santosa mulyadi.sant...@gmail.com wrote: On Thu, Jan 3, 2013 at 7:40 PM, Rahul Bedarkar rpal...@gmail.com wrote: Hi, I was searching for asmlinkage and found that it is already explained at http://kernelnewbies.org/FAQ/asmlinkage But I didn't get this. Can someone tell me about it in brief ? the point is, parameters which is usually passed via stack, is passed using different way. A good example is system call they are passed using registers IIRC -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training
Re: Find out function arguments value from stack pointer
在 2012-12-12，19:28，Manavendra Nath Manav mnm.ker...@gmail.com 写道： On Wed, Dec 12, 2012 at 4:38 PM, Fabio Pozzi pozzi.fa...@gmail.com wrote: When i call print values at offsets starting from __builtin_frame_address (0) the function arguments start from offset 2. How can I confirm that this behavior is always consistent. Arguments are pushed on the stack before the saved frame pointer, thus you have to add an offset equal to the frame pointer address size if you start from the beginning of the saved frame pointer record on the stack. Thanks Fabio! If I execute the same code on ARM arch, does it needs any changes? Arm does not use stack to pass parameters when parameters are less than 4, it uses registers r0 to r3 to pass parameters, and at the beginning of subroutine, r0 to r3 are not stored on stack. So it is complicated to find out parameters from stack as I know. -- Manavendra Nath Manav ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: kernel stack memory
i don't know why you want to corrupt kernel stack by using this method, stack
usually grow from high address to low address, if you allocate a buff in a
function then use memset(), it is writing data from low address to high
address.in your implementation, you allocate an array with 8000*4=32000 bytes (
int arr[8000]; ), then you try to corrupt stack by using memset(), which
operate memory by bytes, rather than by int. so this memset() only corrupt the
first 8192 bytes of the buffer, which is far away from your current task stack.
thread_info locates at the bottom of current task's stack, please
reference the source code of current_thread_info() function of your platform. i
think it is true for X86 or ARM. if you really want to corrupt current
kernel task's stack, please try below code, i did't test it but i think it
should work, at least you can find something from the log: char *sp_addr;
struct thread_info *thread = current_thread_info(); sp_addr = (char*)thread;
printk(sp_addr==thread:%p, task:%p\n, thread, thread-task);
memset (sp_addr, 0x0, 1024);
printk(after corrupt, task:%p, it is dying...\n, thread-task);
Date: Thu, 13 Sep 2012 15:32:05 +0530
Subject: Re: kernel stack memory
From: mujeeb.a...@gmail.com
To: getaru...@gmail.com
CC: shubham20...@gmail.com; kernelnewbies@kernelnewbies.org
Hi,
On Thu, Sep 13, 2012 at 1:59 PM, Arun KS getaru...@gmail.com wrote:
Hello Shubham,
On Thu, Sep 13, 2012 at 12:15 PM, shubham sharma shubham20...@gmail.com
wrote:
Hi,
As far as i know, the size of stack allocated in the kernel space is
8Kb for each process. But in case i use more than 8Kb of memory from
the stack then what will happen? I think that in that case the system
would crash because i am accessing an illegal memory area. I wrote
kernel module in which i defined an integer array whose size was 8000.
But still it did not crash my system. Why?
The module i wrote was as follows:
#include linux/kernel.h
#include linux/module.h
int __init init_my_module(void)
{
int arr[8000];
printk(%s:%d\tmodule initilized\n, __func__, __LINE__);
arr[1] = 1;
arr[4000] = 1;
arr[7999] = 1;
Instead do a memset.
memset(arr, 0, 8192);
If you do this the current calling process thread_info will be set to zero.
This should cause a crash.
I tried and this is also not causing any crash.
Thanks,
Adil
Thanks,
Arun
printk(%s:%d\tarr[1]:%d, arr[4000]:%d, arr[7999]:%d\n, __func__,
__LINE__, arr[1], arr[4000], arr[7999]);
return 0;
}
void __exit cleanup_my_module(void)
{
printk(exiting\n);
return;
}
module_init(init_my_module);
module_exit(cleanup_my_module);
MODULE_LICENSE(GPL);
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RE: setup_thread_stack
Date: Tue, 17 Jul 2012 21:15:50 +0200
Subject: setup_thread_stack
From: francesco.sc...@gmail.com
To: kernelnewbies@kernelnewbies.org
Hi,
I'm totally new to kernel code, just trying to understand the basics of the
core subsystems.
During the do_fork call, there is a call to dup_task_struct, which in turn
calls setup_thread_stack.
What's this call supposed to do? Inside I can see a call to the
task_thread_info macro, but I don't quite understand it:
#define task_thread_info(task) ((struct thread_info *)(task)-stack)
can a task_struct be cast to a thread_info? perhaps my C knowledge should be
improved..I know :(
Sorry for the trivial question..just trying to understand :)
it is nothing about C, but architecture of kernel. kernel put thread_info of
every process at the bottom of stack.
please reference thread_info.h for your specific cpu architecture:
/*
* how to get the thread information struct from C
*/
static inline struct thread_info *current_thread_info(void) __attribute_const__;
static inline struct thread_info *current_thread_info(void)
{
register unsigned long sp asm (sp);
return (struct thread_info *)(sp ~(THREAD_SIZE - 1));
}
because kernel put thread_info at the bottom of stack, so when one process is
running, kernel can use above inline
function to get the thread_info conveniently.
Regards,
Francesco
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RE: Why can not processes switch in atomic context?
Date: Wed, 4 Jul 2012 08:12:25 -0700 Subject: Re: Why can not processes switch in atomic context? From: dhyla...@gmail.com To: bu...@live.cn CC: mobile.parmeni...@gmail.com; kernelnewbies@kernelnewbies.org Hi, On Wed, Jul 4, 2012 at 3:44 AM, 弋天 卜 bu...@live.cn wrote: 在 2012-7-3，22:26，Parmenides mobile.parmeni...@gmail.com 写道： ...snip... 1. For the spinlock case, it is easy to get if preemption is allowed in critical section, the purpose of protection provided by spinlock can not be achieved readily. i think disable preemption in spinlock is not for safe, it is For efficiency. Spinlock should exit as soon as possible. If tank1 get spinlock and goto sleep for 100 seconds before Release spinlock, task2 which requests the same spinlock Should wait for 100 seconds, for this example, mutex should be used instead of spinlock. Unless, of course, the interrupt that fired tried to acquire the spinlock it preempted, in which case you would have deadlock, even on an SMP system, if the same processor happened to be used for both. yes, i think you are right, suppose task1 use spin_lock_irqsave() to get a spinlock, then call schedule() to sleep for a long time, the interrupt on this cpu core will be enabled by kernel, and if there is an interrupt triggered on the same cpu and get the same spinlock, deadlock will happen. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: Why can not processes switch in atomic context?
Date: Wed, 4 Jul 2012 08:12:25 -0700 Subject: Re: Why can not processes switch in atomic context? From: dhyla...@gmail.com To: bu...@live.cn CC: mobile.parmeni...@gmail.com; kernelnewbies@kernelnewbies.org Hi, On Wed, Jul 4, 2012 at 3:44 AM, 弋天 卜 bu...@live.cn wrote: 在 2012-7-3，22:26，Parmenides mobile.parmeni...@gmail.com 写道： ...snip... 1. For the spinlock case, it is easy to get if preemption is allowed in critical section, the purpose of protection provided by spinlock can not be achieved readily. i think disable preemption in spinlock is not for safe, it is For efficiency. Spinlock should exit as soon as possible. If tank1 get spinlock and goto sleep for 100 seconds before Release spinlock, task2 which requests the same spinlock Should wait for 100 seconds, for this example, mutex should be used instead of spinlock. Unless, of course, the interrupt that fired tried to acquire the spinlock it preempted, in which case you would have deadlock, even on an SMP system, if the same processor happened to be used for both. we are talking about schedule in spinlock, but not the synchronization between normal process and interrupt. in your example, it is kernel developer's responsibility to make this correct, this is why kernel give us the API spin_lock_irqsave(). if normal process and interrupt handler will acquire the same spinlock, please use spin_lock_irqsave() instead of spin_lock(). 2. For the interrupt context case, I think when processing interrupt, kernel can be preempted in principle. But, this really increases the interrupt processing time which further cause longer response time and data missing in device. Except that, is there any other reasons? You are right, kernel can schedule in interrupt context, but that will delay the completion of interrupt, which does not make sense, so kernel will not do like this. Note! Kernel can, but should not schedule in interrupt context. Scheduling in an interrupt can hang the system. Lets suppose that A acquires a resource, disabled interrupts and calls schedule. Then B gets scheduled and wants the resource that A is holding so it blocks. But since interrupts were disabled, the timer tick will never fire and you're back into a deadlock situation again. in your example here, i think A is the interrupt handler, rather than a normal task, because we are talking about scheduleing in interrupt handler. if A calls schedule, the interrupted task, let's suppose it is usb task, will go to sleep. let's suppose cpu0 handles the interrupt handler A, and usb task runs on cpu0 also. after A go to sleep, which equals the usb task go to sleep, there must be another new task will be waked up by function switch_to(), let's suppose this lucky guy is BT task, the interrupt on cpu0 could be re-enalbed by function svc_exit() before BT task(or some other tasks) runs. i think disable interrupt on cpu0 inside A does not mean the interrupt can only be re-enabled by A. i am not saying it is good to schedule inside interrupt handler, i just want to make it clear that this can be done, but is not a good behavior and make no sense. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
how to get create/compile time of vmlinux
Hi All:i have a vmlinux file, how can i know when it is created/compiled? thanks. Best Regards ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: how to use the memory allocated in kernel?
Hi :you can find out the meaning in vmalloc.c, function vmalloc().
vmalloc accept only one parameter, the size of memory that you want to
allocate. this function will return the virtual address which you can use to
read/write data inside it. vmalloc hides some implementation details about
real memory allocation, for example: the virtual address thatreturned from
vmalloc() function is continuous, but physical memory can not continuous.
vmalloc() will first call function alloc_vmap_area(), which you mentioned
before, this function will occupy a continuousvirtuall address space in VMALLOC
region, note that it only occupies virtual address space, no physical memory
are mapped tothese virtual address at this moment. so if you operate at this
virtual address as you did before, it is a bug! vmalloc() then call
function __vmalloc_area_node(), which will find out enough non-continuous
physical memory, then modifyPTEs of current task, map the virtual address to
real physical memory. after this, you can operate at the address returned
byalloc_vmap_area(). the example code you did lacks this action, you can try to
add this and test again. i suggest that you use kmalloc() and vmalloc()
directly. if you want to allocate small and physical continuous memory, use
kmalloc().if you want to allocate very large(e.g. 10MB) and physical
non-continuous memory, use vmalloc(). Best Regards
Date: Wed, 18 Apr 2012 18:00:03 +0800
Subject: Re: how to use the memory allocated in kernel?
From: summer...@gmail.com
To: dhyla...@gmail.com
CC: kernelnewbies@kernelnewbies.org
Hi Dave,
Thanks for reply. My English is not very good, and so I want to ask about a
term:map. Does map mean that create a relationship between the virtual space
and physical memory?
Thanks again!
在 2012年4月18日 下午4:17，Dave Hylands dhyla...@gmail.com写道：
Hi ,
On Wed, Apr 18, 2012 at 12:44 AM, 夏业添 summer...@gmail.com wrote:
Hi everyone,
there are some functions can alloc memory in kernel, but it seems that I
cannot use it directly. Here is my code:
static int mytest_vm(){
struct vm_struct *v_start;
v_start=alloc_vm_area(PAGE_SIZE,NULL); //the kernel api has changed,
I don't understand why there is a second parameter
if(v_start==NULL){
printk(cannot alloc page\n);
return -1;
}
sprintf((char *)v_start-addr,this is a test.\n);
printk(after sprintk:%s,(char *)v_start-addr);
free_vm_area(v_start);
return 0;
}
module_init(mytest_vm);
but it just got a kernel Oops. Can anyone explain this to me? Thanks very
much!
If my understanding of things is correct, this just allocates virtual
space. That virtual space isn't backed by any physical pages.
The normal kernel allocators are things like kmalloc and vmalloc.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
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RE: static I/O device mapping of UART for early prints console
Date: Sun, 11 Mar 2012 12:29:44 +0530 Subject: static I/O device mapping of UART for early prints console From: pcuser.ma...@gmail.com To: kernelnewbies@kernelnewbies.org I'm doing kernel porting to arm926 based FPGA board (similar to samsung-s3c6410 board). I'm trying to setup UART for early print and console. I gone through some reference boards(samsung-s3c6410) for setting up uart for early print console. I can't trace the virtual mapping for UART registers in adduart macro in debug-macro.S file .macro addruart, rp, rv ldr \rp, = S3C_PA_UART ldr \rv, = S3C_VA_UART Basically,I want to know how to calculate this virtual address(S3C_VA_UART) from the physical address(S3C_PA_UART) actually, this is io_virtual_address map to io_physical_address, it is not equal to kernel_virtual_adressmap to kernel_physical_address.differenct platform providers such as Qualcomm, TI, STE, Samsung use different fomula to map IO address. for example, for OMAP1, TI use a very simple fomula to map from io_virtual_address to io_physical_address:io_virtual_address = io_physical_address-0x0100 so suppose TI's uart0 physical address is 0xFFFB, then the virtial address of uart0 is 0xFEFB. for Samsung S3c64XX: 1. both physical and virtual address of uart is defined in map.h:#define S3C_PA_UART (0x7F005000) /* See notes on UART VA mapping in debug-macro.S */ #define S3C_VA_UARTx(x) (S3C_VA_UART + (S3C_PA_UART 0xf) + ((x) * S3C_UART_OFFSET))#define S3C_VA_UART0 S3C_VA_UARTx(0) #define S3C_VA_UART1 S3C_VA_UARTx(1) #define S3C_VA_UART2 S3C_VA_UARTx(2) #define S3C_VA_UART3 S3C_VA_UARTx(3) 2. so for uart0, the virtual address will be:virtual_uart0_address = S3C_VA_UART + (S3C_PA_UART 0xf) and in map-base.h:#define S3C_ADDR_BASE (0xF400) #define S3C_VA_UART S3C_ADDR(0x0100) /* UART */ so S3C_VA_UART = 0xF500 3. at last:virtual_uart0_address = S3C_VA_UART + (S3C_PA_UART 0xf)= 0xF500 + (0x7F005xf) = 0xF5005000 please do not try to use __phys_to_virt, this is for kernel virtual address to kernel physical address translation, rather than IO address map. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
How to avoid kernel Oops 0x81F in function do_alignment() ?
Hi experts: an user application generates a un-alignment data abort, then in function do_alignment, kernel read the instruction from the address where data abort occurs by: fault = __get_user(instr, (u32 *)instrptr);after this sentence, instr is the error instruction that generate data abort.i change this instruction from strict alignment check instruction to not strict alignmentcheck instruction by: instr = instr030;at last i write this instruction back to ram, and let cpu execute this instruction again: *((u32*)instrptr) = instr;it works on kernel 2.6.35, but on version 3.0, it failed, the last sentence above generates a Oops: [ 58.966552] Unable to handle kernel paging request at virtual address 84ec [ 58.974029] pgd = db9f4000 [ 58.976806] [84ec] *pgd=1b9db831, *pte=0ae5f59f, *ppte=0ae5fe7e [ 58.986877] Internal error: Oops: 81f [#1] PREEMPT SMP1. it seems that kernel 3.0 can not modify user mode program instructions directly even underSVC mode. 2. how can i change the page permisson before write back instruction of user mode application? for example, find out the page tables of current application, find out the pte which representsthe instruction that generate data abort, then modify pte, write back instruction, restore pte, done.how to do these? please advise, thanks very much. Best Regards ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
is there any Android APK that generate the SIGBUG error because of ARM NEON instructions?
Hi All: anybody who met such error of Android application? the logcat will be something like below: signal 7 (SIGBUS), code 128 (?), fault addr #00 pc 00015cec /data/data/com.pccw.mobile.sip/lib/libavcodec.so --this lib use ARM NEON instructions i found that Linux Kernel(even in latest 3.2 version) does not support un-alignment NEON instruction in data abort handler, if anybody who are interested in this topic, please contact me, i can provide the patch to workaroud it. Best Regards ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: SA_INTERRUPT or SA_SHIRQ
Hi Devendra:can you please tell me your kernel version? SA_INTERRUPT is deprecated for many years. it is changed to be IRQF_DISABLED, which is also deprecated since 2.6.35. in kernel 2.6.35, top half interrupt handler will be called with interrupts disabled, and for SA_SHIRQ, it is changed to be IRQF_SHARED, you should check the return value of request_irq() to see whether your irq can be shared with formerregistered irq which use the same int line. suppose you are registering irq19 for usb, and the BT module has reigstered irq19 with IRQF_SHARED flag, then you are lucky enough to reigter correctly for usb. opposite, if BT module registered irq19 without IRQF_SHARED flag, then BT will use irq19 alone, it means your register for usb will fail . Best Regards Date: Wed, 22 Feb 2012 14:56:41 +0530 Subject: SA_INTERRUPT or SA_SHIRQ From: devendra.rawat.si...@gmail.com To: kernelnewbies@kernelnewbies.org Hi All, If I register an ISR using both the flags SA_INTERRUPT and SA_SHIRQ set, what kind of interrupt line will I get a dedicated one or a shared one ? the exact definition is request_irq(dev-pci_dev-irq, soc_intr, SA_INTERRUPT | SA_SHIRQ, MODULE_NAME, dev); thanks in advance, Devendra ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: pagetables used in interrupt context
Hi Subin: for kernel version 2.6.35, ARM architecture, when interrupt occurs, kernel will change from USER/SVC mode to IRQ mode,backup some registers and change to SVC mode immediately, handle the real interrupt handler in SVC mode, which people say in interrupt context.kernel will use the stack(interrupt context) of interrupted thread to handle the interrupt, and there is no MMU operation which do page table switch.so the thread which is interrupted by interrupt, it's kernel mode stack will be choosed as the interrupt context of current interrupt. Date: Tue, 21 Feb 2012 19:18:32 -0700 Subject: Re: pagetables used in interrupt context From: subingangadha...@gmail.com To: dhyla...@gmail.com CC: kernelnewbies@kernelnewbies.org Thank you for clearing my doubt. On Mon, Feb 20, 2012 at 8:39 PM, Dave Hylands dhyla...@gmail.com wrote: Hi Subin, On Mon, Feb 20, 2012 at 6:47 PM, subin gangadharan subingangadha...@gmail.com wrote: Hi All, Please correct me if I am wrong. In linux each process will have its own page tables, so when a interrupt happens processor will switch to interrupt context and execute the proper handler. So my doubt, if this is the case, interrupt hanlder will be using the pagetables of the interrupted process or is there a separate page table for this. Yep - that's right. Conceptually you can imagine that the kernel page tables are replicated in each process, so when the interrupt occurs, the kernel mappings will always be in effect regardless of which task is running. How this is actually achieved may vary from architecture to architecture. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: pagetables used in interrupt context
Hi : for ARM architecture, from the point of my view, interrupt can be handled in IRQ, SVC, or SYSTEM modes.1.if kernel handles interrupt in IRQ mode, it can use separate specific stack of IRQ mode to handle interrupt,but it cannot support nest interupt, suppose you are running interrupt handler in IRQ mode, a new coming interrupt will corrupt the lr_irq which is used for current function.2. if kernel handles interrupt in SYSTEM mode, the sequences will be : hardware interrupt occurs--IRQ mode--SYSTEM mode --call interrupt handler. kernel can support nest interrupt well by this way, the problem is SYSTEM mode use the same register with USER mode, which means kernel will use the interrupted thread's user mode stack, this will leake information of kernel to user space, so it is not a good idea, although i did this for many years for OMAP chipset(the OS is not linux, it is mixed by REX and my own design.).3. Linux kernel choose the last one, handle interrupt in SVC mode, which can support nest interrupt if it wants(2.6.35 does not support this). and it is very simple to use the interrupted thread's kernel mode stack as the interrupt context. if kernel use a specific stack which is for interrupt only, the sequences will be : hardware interrupt occurs--IRQ mode--SVC mode--backup sp register of interrupted thread to it's TCB---set sp register to be the specific kernel stack address--call interrupt handler---restore sp of interrupted thread---return from interrupt.this is a little complicated compared with the current design. so i agree with the current design. Best Regards Date: Thu, 23 Feb 2012 08:41:28 -0600 Subject: Re: pagetables used in interrupt context From: c.a.subraman...@gmail.com To: bu...@live.cn CC: dhyla...@gmail.com; subingangadha...@gmail.com; kernelnewbies@kernelnewbies.org On Thu, Feb 23, 2012 at 6:52 AM, 卜弋天 bu...@live.cn wrote: Hi Subin: for kernel version 2.6.35, ARM architecture, when interrupt occurs, kernel will change from USER/SVC mode to IRQ mode,backup some registers and change to SVC mode immediately, handle the real interrupt handler in SVC mode, which people say in interrupt context. kernel will use the stack(interrupt context) of interrupted thread to handle the interrupt, and there is no MMU operation which do page table switch. so the thread which is interrupted by interrupt, it's kernel mode stack will be choosed as the interrupt context of current interrupt. Thanks ! thats a terse explanation! Can you please mention why we do not have a IRQ stack (in terms of size of the stack) to do the processing? Date: Tue, 21 Feb 2012 19:18:32 -0700 Subject: Re: pagetables used in interrupt context From: subingangadha...@gmail.com To: dhyla...@gmail.com CC: kernelnewbies@kernelnewbies.org Thank you for clearing my doubt. On Mon, Feb 20, 2012 at 8:39 PM, Dave Hylands dhyla...@gmail.com wrote: Hi Subin, On Mon, Feb 20, 2012 at 6:47 PM, subin gangadharan subingangadha...@gmail.com wrote: Hi All, Please correct me if I am wrong. In linux each process will have its own page tables, so when a interrupt happens processor will switch to interrupt context and execute the proper handler. So my doubt, if this is the case, interrupt hanlder will be using the pagetables of the interrupted process or is there a separate page table for this. Yep - that's right. Conceptually you can imagine that the kernel page tables are replicated in each process, so when the interrupt occurs, the kernel mappings will always be in effect regardless of which task is running. How this is actually achieved may vary from architecture to architecture. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com -- With Regards Subin Gangadharan I am not afraid and I am also not afraid of being afraid. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: pagetables used in interrupt context
Hi Subin: i am not familiar with other architecture, but for ARM, Linux Kernel 2.6.35, i checked the function handle_level_irq()and handle_edge_irq() in chip.c, both of them will call handle_IRQ_event() which is in handle.c. and the function handle_IRQ_event() will call the interrupt handler written by user. Kernel does not open interrupt(ARM CPSR I bit)when calling interrupt handler in handle_IRQ_event() function. this is only for top-half interrupt handling. for bottom-half, it is no doubt that the interrupt will be opened. so if you register a interrupt by request_irq(), the interrupt handler will be called with irq disabled. i tested on Cortex-A9 dual core platform, it is right. Date: Thu, 23 Feb 2012 11:12:06 -0600 Subject: Re: pagetables used in interrupt context From: subingangadha...@gmail.com To: bu...@live.cn CC: c.a.subraman...@gmail.com; dhyla...@gmail.com; kernelnewbies@kernelnewbies.org Hi , can support nest interrupt if it wants(2.6.35 does not support this). and it is very simple to use the interrupted thread's kernel mode stack as the interrupt context. if kernel use a specific stack which is for interrupt Thanks for the crystal clear explanation of the page table usage in interrupt context. I have one more doubt, so in 2.6.35 as you said it doesn't support nested interrupt, does it mean that all other interrupts are completely disabled, (I mean no other can interrupt the processor) while executing an interrupt handler. 2012/2/23 卜弋天 bu...@live.cn: Hi : for ARM architecture, from the point of my view, interrupt can be handled in IRQ, SVC, or SYSTEM modes. 1.if kernel handles interrupt in IRQ mode, it can use separate specific stack of IRQ mode to handle interrupt,but it cannot support nest interupt, suppose you are running interrupt handler in IRQ mode, a new coming interrupt will corrupt the lr_irq which is used for current function. 2. if kernel handles interrupt in SYSTEM mode, the sequences will be : hardware interrupt occurs--IRQ mode--SYSTEM mode --call interrupt handler. kernel can support nest interrupt well by this way, the problem is SYSTEM mode use the same register with USER mode, which means kernel will use the interrupted thread's user mode stack, this will leake information of kernel to user space, so it is not a good idea, although i did this for many years for OMAP chipset(the OS is not linux, it is mixed by REX and my own design.). 3. Linux kernel choose the last one, handle interrupt in SVC mode, which can support nest interrupt if it wants(2.6.35 does not support this). and it is very simple to use the interrupted thread's kernel mode stack as the interrupt context. if kernel use a specific stack which is for interrupt only, the sequences will be : hardware interrupt occurs--IRQ mode--SVC mode--backup sp register of interrupted thread to it's TCB---set sp register to be the specific kernel stack address--call interrupt handler---restore sp of interrupted thread---return from interrupt. this is a little complicated compared with the current design. so i agree with the current design. Best Regards Date: Thu, 23 Feb 2012 08:41:28 -0600 Subject: Re: pagetables used in interrupt context From: c.a.subraman...@gmail.com To: bu...@live.cn CC: dhyla...@gmail.com; subingangadha...@gmail.com; kernelnewbies@kernelnewbies.org On Thu, Feb 23, 2012 at 6:52 AM, 卜弋天 bu...@live.cn wrote: Hi Subin: for kernel version 2.6.35, ARM architecture, when interrupt occurs, kernel will change from USER/SVC mode to IRQ mode,backup some registers and change to SVC mode immediately, handle the real interrupt handler in SVC mode, which people say in interrupt context. kernel will use the stack(interrupt context) of interrupted thread to handle the interrupt, and there is no MMU operation which do page table switch. so the thread which is interrupted by interrupt, it's kernel mode stack will be choosed as the interrupt context of current interrupt. Thanks ! thats a terse explanation! Can you please mention why we do not have a IRQ stack (in terms of size of the stack) to do the processing? Date: Tue, 21 Feb 2012 19:18:32 -0700 Subject: Re: pagetables used in interrupt context From: subingangadha...@gmail.com To: dhyla...@gmail.com CC: kernelnewbies@kernelnewbies.org Thank you for clearing my doubt. On Mon, Feb 20, 2012 at 8:39 PM, Dave Hylands dhyla...@gmail.com wrote: Hi Subin, On Mon, Feb 20, 2012 at 6:47 PM, subin gangadharan subingangadha...@gmail.com wrote: Hi All, Please correct me if I am wrong. In linux each process will have its own page tables, so when a interrupt happens processor will switch to interrupt context and execute the proper handler. So my doubt, if this is the case, interrupt hanlder will be using
RE: arm assembly doubt
Hi: the SWI is used for system APIs such as open, read, write. user mode
applications call system APIs via SWI, which will change ARM mode from USER to
SVC. so when vector_swi is called, Linux will do as below: 1. store
r0~r12, these registers are universal for USR mode SVC mode. 2. store r13
and r14 of USER mode. Note, SWI is triggered from USER mode, so here Linux
store USER mode's r13 and r14, rather than SVC's. for your two
questions: 1. the ^ means to get USER mode registers, rather than current
mode.
2. no matter how you arrange registers in opcode {}, stmdb will always
push lr first, then sp. so after line 348, the stack view is as
below:lr_usrsp_usrr12...r0 Date: Thu, 16 Feb 2012 19:35:17 -0700
Subject: Re: arm assembly doubt
From: subingangadha...@gmail.com
To: su...@gatech.edu
CC: kernelnewbies@kernelnewbies.org
Thanks for the answer. Actually this is what I am trying to understand.
ENTRY(vector_swi)
345 sub sp, sp, #S_FRAME_SIZE
346 stmia sp, {r0 - r12} @ Calling r0 - r12
347 ARM( add r8, sp, #S_PC )
348 ARM( stmdb r8, {sp, lr}^ ) @ Calling sp, lr
349 THUMB( mov r8, sp )
350 THUMB( store_user_sp_lr r8, r10, S_SP ) @ calling sp, lr
351 mrs r8, spsr@ called from
non-FIQ mode, so ok.
352 str lr, [sp, #S_PC] @ Save calling PC
353 str r8, [sp, #S_PSR]@ Save CPSR
354 str r0, [sp, #S_OLD_R0]
In this case after the line number 348(if its in arm mode),will the
kernel stack have the contents
r0-r12,sp,lr in this order or r0-r12,lr,sp this one. Beccause I
believe stmdb r8, {sp, lr}^ will push the sp first then lr. In that
case sp and lr will be interchanged in struct pt_regs.
Please correct me if I am wrong.
On Wed, Feb 15, 2012 at 9:34 PM, Surenkumar Nihalani su...@gatech.edu wrote:
Hi,
On Feb 15, 2012, at 11:30 PM, subin gangadharan wrote:
Hi ,
I am trying to understand how system call is implmented in linux for
arm.And I am not that familiar with arm assembly.
Could any body please help me to understand what exactly this ^ does
in this instruction stmdb r8,{sp,lr}^
--
With Regards
Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.
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Example:
LDFMD sp!, {r0-r12, pc}^
- The ^ qualifier specifies that the CPSR is restored from the SPSR.
It must be used only from a privileged mode.
--
With Regards
Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.
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