* LRS: Reformat a bit to keep text under 80 columns.
+Thu Apr 2 16:52:44 1998 Jason Molenda (crash@bugshack.cygnus.com)
+
+ * LRS: Reformat a bit to keep text under 80 columns.
+
Thu Apr 2 16:10:36 1998 Stan Shebs <shebs@andros.cygnus.com>
* gdb.texinfo: Add some credits, mention bug monitor.
Thu Apr 2 16:10:36 1998 Stan Shebs <shebs@andros.cygnus.com>
* gdb.texinfo: Add some credits, mention bug monitor.
-LRS, or Live Range Splitting is an optimization technique which allows a user
-variable to reside in different locations during different parts of a function.
+LRS, or Live Range Splitting is an optimization technique which allows
+a user variable to reside in different locations during different parts
+of a function.
-For example, a variable might reside in the stack for part of a function and
-in a register during a loop and in a different register during another loop.
+For example, a variable might reside in the stack for part of a function
+and in a register during a loop and in a different register during
+another loop.
-Clearly, if a variable may reside in different locations, then the compiler
-must describe to the debugger where the variable resides for any given part
-of the function.
+Clearly, if a variable may reside in different locations, then the
+compiler must describe to the debugger where the variable resides for
+any given part of the function.
-This document describes the debug format for encoding these extensions in
-stabs.
+This document describes the debug format for encoding these extensions
+in stabs.
-Since these extensions are gcc specific, these additional symbols and stabs
-can be disabled by the gcc command option -gstabs.
+Since these extensions are gcc specific, these additional symbols and
+stabs can be disabled by the gcc command option -gstabs.
GNU extensions for LRS under stabs:
GNU extensions for LRS under stabs:
range symbols:
-------------
range symbols:
-------------
- A range symbol will be used to mark the beginning or end of a live range
- (the range which describes where a symbol is active, or live).
- These symbols will later be referenced in the stabs for debug purposes.
- For simplicity, we'll use the terms "range_start" and "range_end" to
- identify the range symbols which mark the beginning and end of a live
- range respectively.
+ A range symbol will be used to mark the beginning or end of a
+ live range (the range which describes where a symbol is active,
+ or live). These symbols will later be referenced in the stabs for
+ debug purposes. For simplicity, we'll use the terms "range_start"
+ and "range_end" to identify the range symbols which mark the beginning
+ and end of a live range respectively.
- Any text symbol which would normally appear in the symbol table (eg. a
- function name) can be used as range symbol. If an address is needed to
- delimit a live range and does not match any of the values of symbols
- which would normally appear in the symbol table, a new symbol will be
- added to the table whose value is that address.
+ Any text symbol which would normally appear in the symbol table
+ (eg. a function name) can be used as range symbol. If an address
+ is needed to delimit a live range and does not match any of the
+ values of symbols which would normally appear in the symbol table,
+ a new symbol will be added to the table whose value is that address.
The three new symbol types described below have been added for this
purpose.
The three new symbol types described below have been added for this
purpose.
- For efficiency, the compiler should use existing symbols as range symbols
- whenever possible; this reduces the number of additional symbols which
- need to be added to the symbol table.
+ For efficiency, the compiler should use existing symbols as range
+ symbols whenever possible; this reduces the number of additional
+ symbols which need to be added to the symbol table.
New debug symbol type for defining ranges:
New debug symbol type for defining ranges:
- The compiler and debugger view a variable with multiple homes as a primary
- symbol and aliases for that symbol. The primary symbol describes the default
- home of the variable while aliases describe alternate homes for the variable.
+ The compiler and debugger view a variable with multiple homes as
+ a primary symbol and aliases for that symbol. The primary symbol
+ describes the default home of the variable while aliases describe
+ alternate homes for the variable.
- A live range defines the interval of instructions beginning with
- range_start and ending at range_end-1, and is used to specify a range of
- instructions where an alias is active or "live". So, the actual end of
- the range will be one less than the value of the range_end symbol.
+ A live range defines the interval of instructions beginning with
+ range_start and ending at range_end-1, and is used to specify a
+ range of instructions where an alias is active or "live". So,
+ the actual end of the range will be one less than the value of the
+ range_end symbol.
Ranges do not have to be nested. Eg. Two ranges may intersect while
each range contains subranges which are not in the other range.
Ranges do not have to be nested. Eg. Two ranges may intersect while
each range contains subranges which are not in the other range.
range_end, while one symbol's range_start can be another symbol's
range_end.
range_end, while one symbol's range_start can be another symbol's
range_end.
- When a variable's storage class changes (eg. from stack to register, or
- from one register to another), a new symbol entry will be added to
- the symbol table with stabs describing the new type, and appropriate
- live ranges refering to the variable's initial symbol index.
+ When a variable's storage class changes (eg. from stack to register,
+ or from one register to another), a new symbol entry will be
+ added to the symbol table with stabs describing the new type,
+ and appropriate live ranges refering to the variable's initial
+ symbol index.
- For variables which are defined in the source but optimized away, a symbol
- should be emitted with the live range l(0,0).
+ For variables which are defined in the source but optimized away,
+ a symbol should be emitted with the live range l(0,0).
- Live ranges for aliases of a particular variable should always be disjoint.
- Overlapping ranges for aliases of the same variable will be treated as
- an error by the debugger, and the overlapping range will be ignored.
+ Live ranges for aliases of a particular variable should always
+ be disjoint. Overlapping ranges for aliases of the same variable
+ will be treated as an error by the debugger, and the overlapping
+ range will be ignored.
If no live range information is given, the live range will be assumed to
span the symbol's entire lexical scope.
If no live range information is given, the live range will be assumed to
span the symbol's entire lexical scope.
-Assume that "a" lives in the stack at offset -8, except for inside the loop where
-"a" resides in register "r5".
+Assume that "a" lives in the stack at offset -8, except for inside the
+loop where "a" resides in register "r5".
-The way to describe this is to create a stab for the variable "a" which describes
-"a" as living in the stack and an alias for the variable "a" which describes it
-as living in register "r5" in the loop.
+The way to describe this is to create a stab for the variable "a" which
+describes "a" as living in the stack and an alias for the variable "a"
+which describes it as living in register "r5" in the loop.
-Let's assume that "#1" and "#2" are symbols which bound the area where "a" lives
-in a register.
+Let's assume that "#1" and "#2" are symbols which bound the area where
+"a" lives in a register.
The stabs to describe "a" and its alias would look like this:
The stabs to describe "a" and its alias would look like this:
.stabs "#3:r1;l(#1,#2)",64,0,0,5
.stabs "#3:r1;l(#1,#2)",64,0,0,5
-
-
-This design implies that the debugger will keep a chain of aliases for any
-given variable with aliases and that chain will be searched first to find
-out if an alias is active. If no alias is active, then the debugger will
-assume that the main variable is active.
-
-
+This design implies that the debugger will keep a chain of aliases for
+any given variable with aliases and that chain will be searched first
+to find out if an alias is active. If no alias is active, then the
+debugger will assume that the main variable is active.
projects / binutils-gdb.git / commitdiff