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improve warnings

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Brendan Gregg
2015-07-01 12:06:34 -07:00
parent 5103491a8c
commit 2be3c8d079
3 changed files with 15 additions and 8 deletions
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2
examples/uprobe_example.txt
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@@ -285,7 +285,7 @@ version's function names and platform's register usage.
uprobe p:libc:sleep
# trace sleep() with register %di (x86):
uprobe 'p:libc:sleep %di'
# trace this address (use caution, can cause failures):
# trace this address (use caution: must be instruction aligned):
uprobe p:libc:0xbf130
# trace gettimeofday() for PID 1182 only:
uprobe -p 1182 p:libc:gettimeofday

7
man/man8/uprobe.8
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@@ -17,6 +17,11 @@ believe newer kernels (post 4.0) are relatively safer, but use caution. Test
in a lab environment, and know what you are doing, before use. Also consider
other (more developed) user-level tracers (perf_events, LTTng, etc.).
Use extreme caution with the raw address mode: eg, "p:libc:0xbf130". uprobe
does not check for instruction alignment, so tracing the wrong address (eg,
mid-way through a multi-byte instruction) will corrupt the target's memory.
Other tracers (eg, perf_events with debuginfo) check alignment.
Also beware of widespread tracing that interferes with the operation of the
system, eg, tracing libc:malloc, which by-default will trace _all_ processes.
@@ -99,7 +104,7 @@ trace sleep() with register %di (x86):
#
.B uprobe 'p:libc:sleep %di'
.TP
trace this address (use caution, can cause failures):
trace this address (use caution: must be instruction aligned):
#
.B uprobe p:libc:0xbf130
.TP

14
user/uprobe
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@@ -19,6 +19,11 @@
# believe newer kernels (post 4.0) are relatively safer, but use caution. Test
# in a lab environment, and know what you are doing, before use.
#
# Use extreme caution with the raw address mode: eg, "p:libc:0xbf130". uprobe
# does not check for instruction alignment, so tracing the wrong address (eg,
# mid-way through a multi-byte instruction) will corrupt the target's memory.
# Other tracers (eg, perf_events with debuginfo) check alignment.
#
# Also beware of widespread tracing that interferes with the operation of the
# system, eg, tracing libc:malloc, which by-default will trace _all_ processes.
# Test in a lab environment before use.
@@ -90,7 +95,7 @@ function usage {
uprobe p:libc:sleep
# trace sleep() with register %di (x86):
uprobe 'p:libc:sleep %di'
# trace this address (use caution, can cause failures):
# trace this address (use caution: must be instruction aligned):
uprobe p:libc:0xbf130
# trace gettimeofday() for PID 1182 only:
uprobe -p 1182 p:libc:gettimeofday
@@ -180,11 +185,8 @@ function set_addr {
[[ "$base" != 0x* ]] && die "ERROR: finding base load addr"\
"for $path."
addr=$(( addr - base ))
if (( addr < 0 )); then
echo "WARNING: problems removing base addr from $sym." \
"Trying untransposed addr."
addr=$(( addr + base ))
fi
(( addr < 0 )) && die "ERROR: transposed address for $sym"\
"became negative: $addr"
addr=0x$( printf "%x" $addr)
fi
}