Re: [Valgrind-users] Can valgrind print the used "uninitialized value" and its size?

[Maurice v. S. <ma...@bl...>]

Hi Chiaki, 

If you use --track-origins=yes, then valgrind will report where the variable was first allocated (or put on the stack). 

That's usually enough to figure out which it is. 

][ Maurice van Swaaij, Blue Sky Studios ][ 

----- Original Message -----

| From: "chiaki ISHIKAWA" <ish...@yk...>
| To: val...@li...
| Sent: Thursday, April 23, 2015 12:13:38 PM
| Subject: [Valgrind-users] Can valgrind print the used "uninitialized
| value" and its size?

| Hi,

| I was running mozilla TB and found a message during a test run

| ==20163== Conditional jump or move depends on uninitialised value(s)
| ==20163== at 0x90974BC: nsJSObjWrapper::NP_SetProperty(NPObject*,
| void*, _NPVariant const*) (nsJSNPRuntime.cpp:137)
| ...

| so there is an uninitialized usage.

| In this particular instance, I realized that it would be really great
| to know the value of this uninitialized memory (turns out to be
| automatic variable on the stack.)
| so that I can learn what has happened to the subsequent processing.
| Can the uninitialized value was zero or not, for example?

| Can valgrind print value of used uninitialized memory location, say,
| something along the suggested manner below?

| I use the above example:

| ==20163== Conditional jump or move depends on uninitialised value(s)
| ==20163== The value used was: 0xdeadbeaf (4 bytes)
| ==20163== at 0x90974BC: nsJSObjWrapper::NP_SetProperty(NPObject*,
| void*, _NPVariant const*) (nsJSNPRuntime.cpp:137)
| ...

| or maybe considering the possibility of byte block:

| ==20163== Conditional jump or move depends on uninitialised value(s)
| ==20163== The value used started with 0xde 0xad 0xbe 0xaf 0xaa 0xbb
| 0xcc ... (up to the minimum of first N octets or the size of the
| data,
| maybe N can be 16 , etc.)
| ==20163== at 0x90974BC: nsJSObjWrapper::NP_SetProperty(NPObject*,
| void*, _NPVariant const*) (nsJSNPRuntime.cpp:137)

| I believe this simple addition makes the detection very useful
| because it would make creating the suggested patch easier by knowing
| why a program that has been used so long had a hidden issue for so
| many
| years.

| Thank you for sharing this great tool with the programming community.

| Best Regards,
| Chiaki Ishikawa

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