Difference between revisions of "SysRq debugger"
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''SysRq debugger'' can help you to obtain some information from oops-ed kernel. This feature is available since 026test017 kernel. | ''SysRq debugger'' can help you to obtain some information from oops-ed kernel. This feature is available since 026test017 kernel. | ||
| − | == Features == | + | == Features == <!--T:2--> |
''SysRq debugger'' can do one of the following: | ''SysRq debugger'' can do one of the following: | ||
# Dump memory at specified address | # Dump memory at specified address | ||
| Line 7: | Line 9: | ||
# Resolve symbol address by its name | # Resolve symbol address by its name | ||
| − | == How to use it == | + | == How to use it == <!--T:3--> |
To enter debug mode press ''SysRq-g''. | To enter debug mode press ''SysRq-g''. | ||
After this the following commands will be available: | After this the following commands will be available: | ||
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# ''SysRq-q'' - quit debugger | # ''SysRq-q'' - quit debugger | ||
| + | <!--T:4--> | ||
After entering ''-d'', ''-w'' or ''-r'' state you must enter address to work with (and the value you want to write if you do). Simply do this by pressing according keys while holding ''Alt-StsRq''. | After entering ''-d'', ''-w'' or ''-r'' state you must enter address to work with (and the value you want to write if you do). Simply do this by pressing according keys while holding ''Alt-StsRq''. | ||
| + | <!--T:5--> | ||
If you need to enter the upper case letter or the underbar (<code>_</code>) while typing a symbol name then you need to press and release ''shift'' and then the letter or minus (<code>-</code>). | If you need to enter the upper case letter or the underbar (<code>_</code>) while typing a symbol name then you need to press and release ''shift'' and then the letter or minus (<code>-</code>). | ||
| + | <!--T:6--> | ||
At the end press ''enter''. | At the end press ''enter''. | ||
| − | == Working with proc == | + | == Working with proc == <!--T:7--> |
There is a <code>/proc/sysrq-trigger</code> entry which triggers sysrq events. | There is a <code>/proc/sysrq-trigger</code> entry which triggers sysrq events. | ||
You may write a string to it to trigger commands one by one. | You may write a string to it to trigger commands one by one. | ||
There is one note: the string must end with the <code>\r</code> character. | There is one note: the string must end with the <code>\r</code> character. | ||
| − | == Examples == | + | == Examples == <!--T:8--> |
Here are some examples of how to use debugger | Here are some examples of how to use debugger | ||
| − | === Dump memory === | + | === Dump memory === <!--T:9--> |
<pre> | <pre> | ||
# echo -n -e 'gd0xc0000000\rq' > /proc/sysrq-trigger | # echo -n -e 'gd0xc0000000\rq' > /proc/sysrq-trigger | ||
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will dump memory region of 512 bytes | will dump memory region of 512 bytes | ||
| + | <!--T:10--> | ||
<pre> | <pre> | ||
# echo -n -e 'gxq' > /proc/sysrq-trigger | # echo -n -e 'gxq' > /proc/sysrq-trigger | ||
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will dump the next 512 bytes of memory | will dump the next 512 bytes of memory | ||
| − | === Write to memory === | + | === Write to memory === <!--T:11--> |
<pre> | <pre> | ||
# echo -n -e 'gw0xc0000000-0x12345678\rq' > /proc/sysrq-trigger | # echo -n -e 'gw0xc0000000-0x12345678\rq' > /proc/sysrq-trigger | ||
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will write ''0x12345678'' at ''0xc0000000'' | will write ''0x12345678'' at ''0xc0000000'' | ||
| − | === Resolve symbol === | + | === Resolve symbol === <!--T:12--> |
<pre> | <pre> | ||
# echo -n -e 'grschedule\rq' > /proc/sysrq-trigger | # echo -n -e 'grschedule\rq' > /proc/sysrq-trigger | ||
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will print you an address ''schedule()'' function starts from | will print you an address ''schedule()'' function starts from | ||
| + | <!--T:13--> | ||
<pre> | <pre> | ||
# echo -n -e 'gxq' > /proc/sysrq-trigger | # echo -n -e 'gxq' > /proc/sysrq-trigger | ||
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will dump first 512 bytes of it | will dump first 512 bytes of it | ||
| + | <!--T:14--> | ||
Note <i>''-n''</i> and <i>''-e''</i> keys to ''echo'' command. | Note <i>''-n''</i> and <i>''-e''</i> keys to ''echo'' command. | ||
| + | </translate> | ||
[[Category:HOWTO]] | [[Category:HOWTO]] | ||
[[Category:Kernel]] | [[Category:Kernel]] | ||
Latest revision as of 08:37, 26 December 2015
<translate> SysRq debugger can help you to obtain some information from oops-ed kernel. This feature is available since 026test017 kernel.
Contents
Features[edit]
SysRq debugger can do one of the following:
- Dump memory at specified address
- Write arbitrary value to memory at specified address
- Resolve symbol address by its name
How to use it[edit]
To enter debug mode press SysRq-g. After this the following commands will be available:
- SysRq-d - dump memory
- SysRq-w - write to memory
- SysRq-r - resolve symbol
- SysRq-x - go on dumping memory
- ... from the latest address dumped with -d
- ... from the address you wrote to with -w
- ... from the begginning of the symbol resolved with -r
- SysRq-q - quit debugger
After entering -d, -w or -r state you must enter address to work with (and the value you want to write if you do). Simply do this by pressing according keys while holding Alt-StsRq.
If you need to enter the upper case letter or the underbar (_) while typing a symbol name then you need to press and release shift and then the letter or minus (-).
At the end press enter.
Working with proc[edit]
There is a /proc/sysrq-trigger entry which triggers sysrq events.
You may write a string to it to trigger commands one by one.
There is one note: the string must end with the \r character.
Examples[edit]
Here are some examples of how to use debugger
Dump memory[edit]
# echo -n -e 'gd0xc0000000\rq' > /proc/sysrq-trigger
will dump memory region of 512 bytes
# echo -n -e 'gxq' > /proc/sysrq-trigger
will dump the next 512 bytes of memory
Write to memory[edit]
# echo -n -e 'gw0xc0000000-0x12345678\rq' > /proc/sysrq-trigger
will write 0x12345678 at 0xc0000000
Resolve symbol[edit]
# echo -n -e 'grschedule\rq' > /proc/sysrq-trigger
will print you an address schedule() function starts from
# echo -n -e 'gxq' > /proc/sysrq-trigger
will dump first 512 bytes of it
Note -n and -e keys to echo command. </translate>
