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NAME
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stacktrace, localaddr, unwindframe, windindex, windreglocs – stack
traces
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SYNOPSIS
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#include <u.h>
#include <libc.h>
#include <mach.h>
int stacktrace(Map *map, Rgetter rget, Tracer trace)
int localaddr(Map *map, Regs *regs, char *fn, char *val, ulong
*val)
int unwindframe(Map *map, Regs *regs, ulong *next, Symbol *sym)
int windindex(char *regname)
Loc* windreglocs(void)
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DESCRIPTION
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Stacktrace provides machine-independent implementations of process
stack traces. They must retrieve data and register contents from
an executing image. Sometimes the desired registers are not the
current registers but rather a set of saved registers stored elsewhere
in memory. The caller may specify an initial register set in the
form of an Rgetter
function, of the form
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ulong rget(Map *map, char *name)
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It returns the contents of a register when given a map and a register
name. It is usually sufficient for the register function to return
meaningful values only for SP and PC, and for the link register
(usually LR) on CISC machines.
Given the map and the rgetter, stacktrace unwinds the stack starting
at the innermost function. At each level in the trace, it calls
the tracer function, which has the form
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int trace(Map *map, ulong pc, ulong callerpc,
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The tracer is passed the map, the current program counter, the
program counter of the caller (zero if the caller is unknown),
a new rget function, and a symbol (see mach-symbol(3)) describing
the current function (nil if no symbol is known). The value returned
by the tracer controls whether the stack trace continues: a zero
or negative return value stops
the trace, while a positive return value continues it.
The rgetter passed to the tracer is not the rgetter passed to
stacktrace itself. Instead, it is a function returning the register
values at the time of the call, to the extent that they can be
reconstructed. The most common use for this rgetter is as an argument
to lget4, etc., when evaluating the locations of local variables.
Localaddr uses stacktrace to walk up the stack looking for the
innermost instance of a function named fn ; once it finds the
function, it looks for the parameter or local variable var, storing
the address of the variable in val.
Unwindframe is the low-level function on which stacktrace is built.
Given the current memory image in map and the current register
set in regs , unwindframe fills in next with the values of the
register set at the time of the call to the function in the current
program counter. Sym should be the symbol corresponding to the
current function, if available.
The next array holds only the winding registers, typically the
caller-save registers and the program counter and stack pointer.
The order of registers in the array is called the winding order.
The winding set can be found in the array mach−>windreg, which
has mach−>nwindreg entries. Windindex returns the index of the
named register in the winding
order. Windreglocs returns an array of Loc structures corresponding
to the winding registers, in the winding order.
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EXAMPLE
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The following code writes a simple stack trace to standard output,
stopping after at most 20 stack frames.
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static int
trace(Map *map, ulong pc, ulong callerpc,
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Rgetter rget, Symbol *s, int depth)
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{
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char buf[512];
int i, first;
u32int v;
Symbol s2;
if(sym)
print("%s+%lx", s->name, pc - loceval(s->loc));
else
print("%lux", pc);
print("(");
first = 0;
for(i=0; indexlsym(s, &i, &s2)>=0; i++){
if(s.class != CPARAM)
continue;
if(first++)
print(", ");
if(lget4(map, rget, s->loc, &v) >= 0)
print("%s=%#lux", s->name, (ulong)v);
else
print("%s=???", s->name);
}
print(") called from ");
symoff(buf, sizeof buf, callerpc, CTEXT);
print("%s\n", buf);
return depth < 20;
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}
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if(stacktrace(map, nil, trace) <= 0)
print("no stack frame0);
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SOURCE
SEE ALSO
BUGS
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