SSP(1)

NAME
 - Single-step profile COMMAND

SYNOPSIS
ssp [options] low_pc high_pc command...

OPTIONS

-c, --console-trace
    trace every EIP value to the console. *Lots* slower.

-d, --disable
    disable single-stepping by default; use OutputDebugString ("ssp on") to enable stepping

-e, --enable
    enable single-stepping by default; use OutputDebugString ("ssp off") to disable stepping

-h, --help
    output usage information and exit

-l, --dll
    enable dll profiling. A chart of relative DLL usage is produced after the run.

-s, --sub-threads
    trace sub-threads too. Dangerous if you have race conditions.

-t, --trace-eip
    trace every EIP value to a file TRACE.SSP. This gets big *fast*.

-v, --verbose
    output verbose messages about debug events.

-V, --version
    output version information and exit

Example: ssp 0x401000 0x403000 hello.exe

DESCRIPTION
 SSP - The Single Step Profiler

 Original Author: DJ Delorie

 The SSP is a program that uses the Win32 debug API to run a program one ASM instruction at a time. It records the location of each instruction used, how many times that instruction is used, and all function calls. The results are saved in a format that is usable by the profiling program gprof, although gprof will claim the values are seconds, they really are instruction counts. More on that later.

 Because the SSP was originally designed to profile the cygwin DLL, it does not automatically select a block of code to report statistics on. You must specify the range of memory addresses to keep track of manually, but it's not hard to figure out what to specify. Use the "objdump" program to determine the bounds of the target's ".text" section. Let's say we're profiling cygwin1.dll. Make sure you've built it with debug symbols (else gprof won't run) and run objdump like this:

$ objdump -h cygwin1.dll

It will print a report like this:

cygwin1.dll: file format pei-i386
Sections:
Idx Name Size VMA LMA File off Algn
  0 .text 0007ea00 61001000 61001000 00000400 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE, DATA
  1 .data 00008000 61080000 61080000 0007ee00 2**2
                  CONTENTS, ALLOC, LOAD, DATA
  . . .

 The only information we're concerned with are the VMA of the .text section and the VMA of the section after it (sections are usually contiguous; you can also add the Size to the VMA to get the end address). In this case, the VMA is 0x61001000 and the ending address is either 0x61080000 (start of .data method) or 0x0x6107fa00 (VMA+Size method).

 There are two basic ways to use SSP - either profiling a whole program, or selectively profiling parts of the program.

 To profile a whole program, just run ssp without options. By default, it will step the whole program. Here's a simple example, using the numbers above:

$ ssp 0x61001000 0x61080000 hello.exe

This will step the whole program. It will take at least 8 minutes on a PII/300 (yes, really). When it's done, it will create a file called "gmon.out". You can turn this data file into a readable report with gprof:

$ gprof -b cygwin1.dll

The "-b" means 'skip the help pages'. You can omit this until you're familiar with the report layout. The gprof documentation explains a lot about this report, but ssp changes a few things. For example, the first part of the report reports the amount of time spent in each function, like this:

Each sample counts as 0.01 seconds.
  % cumulative self self total
 time seconds seconds calls ms/call ms/call name
 10.02 231.22 72.43 46 1574.57 1574.57 strcspn
  7.95 288.70 57.48 130 442.15 442.15 strncasematch

The "seconds" columns are really CPU opcodes, 1/100 second per opcode. So, "231.22" above means 23,122 opcodes. The ms/call values are 10x too big; 1574.57 means 157.457 opcodes per call. Similar adjustments need to be made for the "self" and "children" columns in the second part of the report.

 OK, so now we've got a huge report that took a long time to generate, and we've identified a spot we want to work on optimizing. Let's say it's the time() function. We can use SSP to selectively profile this function by using OutputDebugString() to control SSP from within the program. Here's a sample program:

    #include <windows.h>
    main()
    {
      time_t t;
      OutputDebugString("ssp on");
      time(&t);
      OutputDebugString("ssp off");
    }

 Then, add the -d option to ssp to default to *disabling* profiling. The program will run at full speed until the first OutputDebugString, then step until the second. You can then use gprof (as usual) to see the performance profile for just that portion of the program's execution.

 There are many options to ssp. Since step-profiling makes your program run about 1,000 times slower than normal, it's best to understand all the options so that you can narrow down the parts of your program you need to single-step.

 -v - verbose. This prints messages about threads starting and stopping, OutputDebugString calls, DLLs loading, etc.

 -t and -c - tracing. With -t, *every* step's address is written to the file "trace.ssp". This can be used to help debug functions, since it can trace multiple threads. Clever use of scripts can match addresses with disassembled opcodes if needed. Warning: creates *huge* files, very quickly. -c prints each address to the console, useful for debugging key chunks of assembler. Use addr2line -C -f -s -e foo.exe < trace.ssp > lines.ssp and then perl cvttrace to convert to symbolic traces.

 -s - subthreads. Usually, you only need to trace the main thread, but sometimes you need to trace all threads, so this enables that. It's also needed when you want to profile a function that only a subthread calls. However, using OutputDebugString automatically enables profiling on the thread that called it, not the main thread.

 -l - dll profiling. Generates a pretty table of how much time was spent in each dll the program used. No sense optimizing a function in your program if most of the time is spent in the DLL. I usually use the -v, -s, and -l options:

$ ssp -v -s -l -d 0x61001000 0x61080000 hello.exe

COPYRIGHT
Cygwin is Copyright (C) 1995-2010 Red Hat, Inc.

Cygwin is Free software; for complete licensing information, refer to: http://cygwin.com/licensing.html

SEE ALSO
The full documentation to the Cygwin API is maintained on the web at: http://cygwin.com/cygwin-api/cygwin-api.html The website is updated more frequently than the man pages and should be considered the authoritative source of information.