bt

Thebtcommand displays a function call backtrace.

Format

The format for the bt command is:

	bt [-v] [ cnt]

where:

-v	specifies that each function’s stackframe base address and size should be displayed.
cnt	specifies the number of lines to be displayed.

When invoking this command with no options, the backtrace displays the names and up to four arguments for each level of stackframe.

Functional Description

The bt command displays a list of function calls, starting with the function in which the User Stack register currently lies, and finishing when a return address becomes ‘‘invalid’’. An address is deemed invalid if it does not lie within one of the ranges specified by the validpcenvironment variable.
 

Each line of output gives the current position in a function, and up to four of its arguments. The arguments can only be retrieved if they are saved within the function prologue, and this is unlikely to be the case for assembler functions and optimized C code. If you want to be able to see the arguments to C functions, then compile your program with optimization disabled. If the -v option is given, then the command additionally displays the stack-frame base address and size for each function. It will also indicate the amount of dynamic stack space allocated using C’s alloca() function, or equivalent.

 

The output of this command is passed to the more command, letting the user view one screenful of output at a time. Optionally, the user can specify cnt, which limits the number of lines to that number. An example illustrating the use of the bt command follows.

Example illustrating the use of the bt command follows. (MIPS code)
 

PMON> c write+10 
    write+0x0010     3c09a07f   lui        t1,0xa07f 
PMON> bt 
    write+0x0010    (0x00000001,0xa0030300,0x0000001c) 
   flsbuf+0x0234    (0xa0030300,0xa0029030) 
   printf+0x045c    (0xa0025490,0xa0020000,0x000000001,0x00000010) 
     main+0x0138    (0x00000001,0xa07ffffe0)     
   _start+0x0040    () 

See Also

See also the more command

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