UNIX V6 dump analysis - Revision history

Jnc: minor clarifications; mention dumping to disk, ext link to code

2022-07-02T10:07:42Z

minor clarifications; mention dumping to disk, ext link to code

Vaxorcist: /* Kernel stack top */ Fixed typo

2022-07-02T07:23:47Z

‎Kernel stack top: Fixed typo

Jnc: /* Swappable per-process data */ only for stock V6

2020-06-14T15:07:27Z

‎Swappable per-process data: only for stock V6

Jnc: +See also

2019-03-03T01:21:50Z

+See also

Jnc: Jnc moved page Unix V6 dump analysis to UNIX V6 dump analysis: Use consistent caps

2019-02-13T13:34:18Z

Jnc moved page Unix V6 dump analysis to UNIX V6 dump analysis: Use consistent caps

Jnc: /* Kernel stack top */ Add trap return PC

2019-02-05T00:28:37Z

‎Kernel stack top: Add trap return PC

Jnc: /* Memory layouts */ Further clarify

2019-02-02T00:30:13Z

‎Memory layouts: Further clarify

Jnc: clarifications

2019-02-01T19:52:27Z

clarifications

Jnc: add memory layout

2019-02-01T01:08:07Z

add memory layout

Jnc: /* Swappable per-process data */ clarify

2019-01-30T23:51:33Z

‎Swappable per-process data: clarify

@@ Line 1: / Line 1: @@
-There are two kinds of dump analysis on [[UNIX Sixth Edition|UNIX V6]], with some overlap between the two.
+There are two kinds of dump analysis on the [[UNIX Sixth Edition|UNIX V6]] [[operating system]], with some overlap between the two.
 The first is of the 'core dump' of an individual [[process]] into a [[file]], created either by a [[user]]'s request (typing '^\' in standard V6), or by any of the error conditions (odd [[address]], etc) which cause a process abort and core dump.
-The second is of a dump of the complete [[main memory]] of a [[PDP-11]] running Unix; the system as distributed only supports doing such dumps to [[magnetic tape]]. This can be done either after the [[operating system|OS]] does a 'panic', which it does when something happens it can't recover from; or after [[halt]]ing the [[Central Processing Unit|CPU]].
+The second is of a dump of the complete [[main memory]] of a [[PDP-11]] running Unix; the system as distributed only supports doing such dumps to [[magnetic tape]] (although sites whose machine lacked a [[magnetic tape drive]] often modified the code to dump to a [[disk]] partition). This can be done either after the [[kernel]] does a 'panic', which it does when something happens it can't recover from; or after [[halt]]ing the [[Central Processing Unit|CPU]].
 ==Memory layouts==
-Unix stores almost all of the writeable data of a process - both the [[swapping|swappable]] data 'belonging' to the [[kernel]] (consisting of per-process data, kept in a 'user' [[structure]], and the per-process kernel [[stack]]), as well as the user's data (both the data area, and the user stack) in a single contiguous block in main memory, and they are all always moved in and out (by swapping, or in a process core dump) as a unit.
+Unix stores almost all of the writeable data of a process - both the [[swapping|swappable]] data 'belonging' to the kernel (consisting of per-process data, kept in a 'user' [[structure]], and the per-process kernel [[stack]]), as well as the user's data (both the data area, and the user stack) in a single contiguous block in main memory, and they are all always moved in and out (by swapping, or in a process core dump) as a unit.
 The order of the layout within that is:
@@ Line 16: / Line 16: @@
 * user stack
-Note that although the user data and stack are contiguous in physical memory (and thus in a core dump, of either kind), they are not contiguous in the process [[virtual address]] space; the [[PDP-11 Memory Management]] separates them there.
+Note that although the user data and stack are contiguous in physical memory (and thus in a core dump, of either kind), they are not contiguous in the process [[virtual address]] [[address space|space]]; the [[PDP-11 Memory Management]] separates them there.
-For information about the memory layout of the kernel itself, see [[Unix V6 kernel memory layout]].
+For information about the physical memory layout of the kernel itself, see [[Unix V6 kernel memory layout]].
 ==Kernel stack top==
@@ Line 29: / Line 29: @@
 | 0 || Old [[Processor Status Word|PS]]
 |-
-| 2 || Old [[Program Counter|PC]]
+| -2 || Old [[Program Counter|PC]]
 |-
-| 4 || R0
+| -4 || R0
 |-
-| 6 || New PS
+| -6 || New PS
 |-
-| 10 || R1
+| -010 || R1
 |-
-| 12 || User [[Stack Pointer|SP]]
+| -012 || User [[Stack Pointer|SP]]
 |-
-| 14 || Index (trap type, or device number)
+| -014 || Index (trap type, or device number)
 |-
-| 16 || Return PC from call to trap() (value depends on contents of l.s)
+| -016 || Return PC from call to trap() (value depends on contents of l.s)
 |-
-| 20 || R5
+| -020 || R5
 |-
-| 22 || R4
+| -022 || R4
 |-
-| 24 || R3
+| -024 || R3
 |-
-| 26 || R2
+| -026 || R2
 |}
-The offset is from the top of the kernel stack, and is negative from there. In a process core dump, this starts at 01776 in the core dump file; in a dump of main memory, it is necessary to know the contents of kernel segment 6's [[PDP-11 Memory Management|address register]], and the kernel stack top is 01776 above the location pointed to by that.
+The offset is from the top of the kernel stack. In a process core dump, this starts at 01776 in the core dump file; in a dump of main memory, it is necessary to know the contents of kernel segment 6's [[PDP-11 Memory Management|address register]], and the kernel stack top is 01776 above the location pointed to by that.
 ==Swappable per-process data==
@@ Line 149: / Line 149: @@
 ** [[Running Unix v6 in SIMH]]
 * [[Installing UNIX Sixth Edition on Ersatz-11]]
 [[Category: UNIX Practical Guides]]

@@ Line 52: / Line 52: @@
 |}
-The offset is from the top of the karnel stack, and is negative from there. In a process core dump, this starts at 01776 in the core dump file; in a dump of main memory, it is necessary to know the contents of kernel segment 6's [[PDP-11 Memory Management|address register]], and the kernel stack top is 01776 above the location pointed to by that.
+The offset is from the top of the kernel stack, and is negative from there. In a process core dump, this starts at 01776 in the core dump file; in a dump of main memory, it is necessary to know the contents of kernel segment 6's [[PDP-11 Memory Management|address register]], and the kernel stack top is 01776 above the location pointed to by that.
 ==Swappable per-process data==

@@ Line 136: / Line 136: @@
 |}
-(See the file 'user.h' for the meanings/contents of the various fields.)
+(See the file 'user.h' for the meanings/contents of the various fields. Also, many V6 instances are modified; these offsets will not be applicable if the user structure has been modified.)
 ==See also==

← Older revision		Revision as of 01:21, 3 March 2019
Line 137:		Line 137:

	(See the file 'user.h' for the meanings/contents of the various fields.)		(See the file 'user.h' for the meanings/contents of the various fields.)
		+
		+	==See also==
		+
		+	* [[UNIX V6 internals]]
		+	* [[Unix V6 kernel memory layout]]
		+	* [[Upgrading UNIX Sixth Edition‎]]
		+	* [[Installing UNIX Sixth Edition]]
		+	** [[Setting up UNIX Sixth Edition]]
		+	* [[Running UNIX V6 on an -11/23]]
		+	* [[Installing Unix v6 (PDP-11) on SIMH]]
		+	** [[Running Unix v6 in SIMH]]
		+	* [[Installing UNIX Sixth Edition on Ersatz-11]]

	[[Category: UNIX Practical Guides]]		[[Category: UNIX Practical Guides]]

@@ Line 41: / Line 41: @@
 | 14 || Index (trap type, or device number)
 |-
-| 16 || R5
+| 16 || Return PC from call to trap() (value depends on contents of l.s)
 |-
-| 20 || R4
+| 22 || R4
 |-
-| 22 || R3
+| 24 || R3
 |-
-| 24 || R2
+| 26 || R2
 |}

← Older revision	Revision as of 13:34, 13 February 2019
(No difference)

@@ Line 4: / Line 4: @@
 The second is of a dump of the complete [[main memory]] of a [[PDP-11]] running Unix; the system as distributed only supports doing such dumps to [[magnetic tape]]. This can be done either after the [[operating system|OS]] does a 'panic', which it does when something happens it can't recover from; or after [[halt]]ing the [[Central Processing Unit|CPU]].
 ==Kernel stack top==
-For both process core dumps, and for system dumps after a panic, since all [[trap]]s and [[interrupt]]s come in through basically the same code, the base of the [[kernel]] [[stack]] will have the same format:
+For both process core dumps, and for system dumps after a panic, since all [[trap]]s and [[interrupt]]s come in through basically the same code, the base of the kernel stack will have the same format:
 {| class="wikitable"
@@ Line 39: / Line 54: @@
 ==Swappable per-process data==
-The [[swapping|swappable]] per-process data is kept in a 'user' [[structure]], contiguous with the per-process kernel stack. In a process core dump (where they are found at the start of the 'core' file), as well as a system dump (where runnable processes can be located via their entries in the process table), the data in this structure may be of relevance and interest.
+The per-process data kept in the 'user' structure are included in both a process core dump (where they are found at the start of the 'core' file), as well as a system dump (where runnable processes loaded into main memory can be located via their entries in the process table); the data in this structure may be of relevance and interest.
 The offsets of the various fields in the structure are: