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This chapter describes the Callgrind Profile Format, Version 1.
A synonymous name is "Calltree Profile Format". These names actually mean the same since Callgrind was previously named Calltree.
The format description is meant for the user to be able to understand the file contents; but more important, it is given for authors of measurement or visualization tools to be able to write and read this format.
The profile data format is ASCII based. It is written by Callgrind, and it is upwards compatible to the format used by Cachegrind (ie. Cachegrind uses a subset). It can be read by callgrind_annotate and KCachegrind.
This chapter gives on overview of format features and examples. For detailed syntax, look at the format reference.
Each file has a header part of an arbitrary number of lines of the format "key: value". After the header, lines specifying profile costs follow. Everywhere, comments on own lines starting with '#' are allowed. The header lines with keys "positions" and "events" define the meaning of cost lines in the second part of the file: the value of "positions" is a list of subpositions, and the value of "events" is a list of event type names. Cost lines consist of subpositions followed by 64-bit counters for the events, in the order specified by the "positions" and "events" header line.
The "events" header line is always required in contrast to the optional line for "positions", which defaults to "line", i.e. a line number of some source file. In addition, the second part of the file contains position specifications of the form "spec=name". "spec" can be e.g. "fn" for a function name or "fl" for a file name. Cost lines are always related to the function/file specifications given directly before.
The event names in the following example are quite arbitrary, and are not related to event names used by Callgrind. Especially, cycle counts matching real processors probably will never be generated by any Valgrind tools, as these are bound to simulations of simple machine models for acceptable slowdown. However, any profiling tool could use the format described in this chapter.
events: Cycles Instructions Flops fl=file.f fn=main 15 90 14 2 16 20 12
The above example gives profile information for event types "Cycles", "Instructions", and "Flops". Thus, cost lines give the number of CPU cycles passed by, number of executed instructions, and number of floating point operations executed while running code corresponding to some source position. As there is no line specifying the value of "positions", it defaults to "line", which means that the first number of a cost line is always a line number.
Thus, the first cost line specifies that in line 15 of source file
Note that regular cost lines always give self (also called exclusive)
cost of code at a given position. If you specify multiple cost lines for the
same position, these will be summed up. On the other hand, in the example above
there is no specification of how many times function
The most important extension to the original format of Cachegrind is the ability to specify call relationship among functions. More generally, you specify associations among positions. For this, the second part of the file also can contain association specifications. These look similar to position specifications, but consist of two lines. For calls, the format looks like
calls=(Call Count) (Destination position) (Source position) (Inclusive cost of call)
The destination only specifies subpositions like line number. Therefore, to be able to specify a call to another function in another source file, you have to precede the above lines with a "cfn=" specification for the name of the called function, and optionally a "cfi=" specification if the function is in another source file ("cfl=" is an alternative specification for "cfi=" because of historical reasons, and both should be supported by format readers). The second line looks like a regular cost line with the difference that inclusive cost spent inside of the function call has to be specified.
Other associations are for example (conditional) jumps. See the reference below for details.
The following example shows 3 functions,
events: Instructions fl=file1.c fn=main 16 20 cfn=func1 calls=1 50 16 400 cfi=file2.c cfn=func2 calls=3 20 16 400 fn=func1 51 100 cfi=file2.c cfn=func2 calls=2 20 51 300 fl=file2.c fn=func2 20 700
One can see that in
With the introduction of association specifications like calls it is needed to specify the same function or same file name multiple times. As absolute filenames or symbol names in C++ can be quite long, it is advantageous to be able to specify integer IDs for position specifications. Here, the term "position" corresponds to a file name (source or object file) or function name.
To support name compression, a position specification can be not only of the format "spec=name", but also "spec=(ID) name" to specify a mapping of an integer ID to a name, and "spec=(ID)" to reference a previously defined ID mapping. There is a separate ID mapping for each position specification, i.e. you can use ID 1 for both a file name and a symbol name.
With string compression, the example from 1.4 looks like this:
events: Instructions fl=(1) file1.c fn=(1) main 16 20 cfn=(2) func1 calls=1 50 16 400 cfi=(2) file2.c cfn=(3) func2 calls=3 20 16 400 fn=(2) 51 100 cfi=(2) cfn=(3) calls=2 20 51 300 fl=(2) fn=(3) 20 700
As position specifications carry no information themselves, but only change the meaning of subsequent cost lines or associations, they can appear everywhere in the file without any negative consequence. Especially, you can define name compression mappings directly after the header, and before any cost lines. Thus, the above example can also be written as
events: Instructions # define file ID mapping fl=(1) file1.c fl=(2) file2.c # define function ID mapping fn=(1) main fn=(2) func1 fn=(3) func2 fl=(1) fn=(1) 16 20 ...
If a Callgrind data file should hold costs for each assembler instruction of a program, you specify subposition "instr" in the "positions:" header line, and each cost line has to include the address of some instruction. Addresses are allowed to have a size of 64 bits to support 64-bit architectures. Thus, repeating similar, long addresses for almost every line in the data file can enlarge the file size quite significantly, and motivates for subposition compression: instead of every cost line starting with a 16 character long address, one is allowed to specify relative addresses. This relative specification is not only allowed for instruction addresses, but also for line numbers; both addresses and line numbers are called "subpositions".
A relative subposition always is based on the corresponding subposition of the last cost line, and starts with a "+" to specify a positive difference, a "-" to specify a negative difference, or consists of "*" to specify the same subposition. Because absolute subpositions always are positive (ie. never prefixed by "-"), any relative specification is non-ambiguous; additionally, absolute and relative subposition specifications can be mixed freely. Assume the following example (subpositions can always be specified as hexadecimal numbers, beginning with "0x"):
positions: instr line events: ticks fn=func 0x80001234 90 1 0x80001237 90 5 0x80001238 91 6
With subposition compression, this looks like
positions: instr line events: ticks fn=func 0x80001234 90 1 +3 * 5 +1 +1 6
Remark: For assembler annotation to work, instruction addresses have to be corrected to correspond to addresses found in the original binary. I.e. for relocatable shared objects, often a load offset has to be subtracted.
For the visualization to be able to show cost percentage, a sum of the cost of the full run has to be known. Usually, it is assumed that this is the sum of all cost lines in a file. But sometimes, this is not correct. Thus, you can specify a "summary:" line in the header giving the full cost for the profile run. An import filter may use this to show a progress bar while loading a large data file.
Event types for cost lines are specified in the "events:" line with an abbreviated name. For visualization, it makes sense to be able to specify some longer, more descriptive name. For an event type "Ir" which means "Instruction Fetches", this can be specified the header line
event: Ir : Instruction Fetches events: Ir Dr
In this example, "Dr" itself has no long name associated. The order of "event:" lines and the "events:" line is of no importance. Additionally, inherited event types can be introduced for which no raw data is available, but which are calculated from given types. Suppose the last example, you could add
event: Sum = Ir + Dr
to specify an additional event type "Sum", which is calculated by adding costs for "Ir and "Dr".
ProfileDataFile := FormatVersion? Creator? PartData*
FormatVersion := "version:" Space* Number "\n"
Creator := "creator:" NoNewLineChar* "\n"
PartData := (HeaderLine "\n")+ (BodyLine "\n")+
HeaderLine := (empty line) | ('#' NoNewLineChar*) | PartDetail | Description | EventSpecification | CostLineDef
PartDetail := TargetCommand | TargetID
TargetCommand := "cmd:" Space* NoNewLineChar*
TargetID := ("pid"|"thread"|"part") ":" Space* Number
Description := "desc:" Space* Name Space* ":" NoNewLineChar*
EventSpecification := "event:" Space* Name InheritedDef? LongNameDef?
InheritedDef := "=" InheritedExpr
InheritedExpr := Name | Number Space* ("*" Space*)? Name | InheritedExpr Space* "+" Space* InheritedExpr
LongNameDef := ":" NoNewLineChar*
CostLineDef := "events:" Space* Name (Space+ Name)* | "positions:" "instr"? (Space+ "line")?
BodyLine := (empty line) | ('#' NoNewLineChar*) | CostLine | PositionSpecification | AssociationSpecification
CostLine := SubPositionList Costs?
SubPositionList := (SubPosition+ Space+)+
SubPosition := Number | "+" Number | "-" Number | "*"
Costs := (Number Space+)+
PositionSpecification := Position "=" Space* PositionName
Position := CostPosition | CalledPosition
CostPosition := "ob" | "fl" | "fi" | "fe" | "fn"
CalledPosition := " "cob" | "cfi" | "cfl" | "cfn"
PositionName := ( "(" Number ")" )? (Space* NoNewLineChar* )?
AssociationSpecification := CallSpecification | JumpSpecification
CallSpecification := CallLine "\n" CostLine
CallLine := "calls=" Space* Number Space+ SubPositionList
JumpSpecification := ...
Space := " " | "\t"
Number := HexNumber | (Digit)+
Digit := "0" | ... | "9"
HexNumber := "0x" (Digit | HexChar)+
HexChar := "a" | ... | "f" | "A" | ... | "F"
Name = Alpha (Digit | Alpha)*
Alpha = "a" | ... | "z" | "A" | ... | "Z"
NoNewLineChar := all characters without "\n"
The header has an arbitrary number of lines of the format "key: value". Possible key values for the header are:
There exist lines
Position specifications allowed:
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