Then the fix is to link both the object file from foo.c and undefinedreference.c, or to compile both the source files:Valgrind is a flexible program for debugging and profiling Linux. An alternative situation arises where the source for foo() is in a separate source file foo.c (and theres a header foo.h to declare foo() that is included in both foo.c and undefinedreference.c). Now this code will compile.It uses /usr/bin/basename as part of its preprocessing, and then invokes /usr/lib/firefox-3.0.9/firefox, which is the real firefox, via ‘exec’. /usr/bin/firefox is a start-up shell script. For example, when I invoke ‘firefox’ on my Linux box, I’m really running three programs. One feature of such programs is that often they create multiple processes.I’d love to hear feedback from Valgrind users about these suggestions. Malloc implementation because if malloc is not fast enough, application writers are.In this post I’m going to make several suggestions for improvements to Valgrind to it easier for users to use with multi-process programs. Unfortunately here you will see that Valgrind seems to not be able to tell you exactly where the problem is occurring.However, I know valgrind can be made to work with custom allocators. Valgrind can help us find the (seemingly invisible) problem. The program should not have crashed but there is still an issue with the file.
Valgrind Not Working For C Program Code Will Compile(In contrast, if we traced by default and you didn’t want that behaviour, the fact that you’d get one Valgrind start-up message per process makes it clearer what’s happening.)Furthermore, in my experience, –trace-children=no is almost never what you want. We even have an entry in the FAQ about this. First of all, it’s quite unclear what’s happening, especially if you don’t understand Valgrind’s behaviour. So Valgrind is tracing /usr/bin/firefox, but /usr/bin/basename and /usr/lib/firefox-3.0.9/firefox are run natively.In order to trace into child processes, you have to use the –trace-children=yes option then it’ll do what you want.But I think that not tracing by default is a bad idea. Where’s that slow-down due to Valgrind? And where are the error messages from Valgrind? As it happens, by default Valgrind doesn’t trace into any child processes spawned by the program it’s tracing. Code 128 ttfIn fact, I cheated, by also using the -v option. The third start-up message is for /usr/lib/firefox-3.0.9/firefox the PID 9658 is reused because /usr/lib/firefox-3.0.9/firefox is invoked with ‘exec’, which reuses the same process — this also explains why there are only two shut-down messages.But working this out isn’t easy. The second (PID 9659) is for /usr/bin/basename. What’s going on? The first start-up message (PID 9658) is for /usr/bin/firefox. Proposal 2: show what command is being runIf I invoke “valgrind –trace-children=yes firefox”, let it load the default page, and then quit, I get this output (eliding some of the startup/shutdown messages for brevity): =9658= Memcheck, a memory error detector.=9659= Memcheck, a memory error detector.=9659= ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 8 from 1)=9658= Memcheck, a memory error detector.=9658= Syscall param write(buf) points to uninitialised byte(s)=9658= at 0x4E38E90: _write_nocancel (in /lib/libpthread-2.8.90.so)=9658= by 0xE55DEFE: ? (in /usr/lib/libICE.so.6.3.0)=9658= Address 0x5e91964 is 12 bytes inside a block of size 1,024 alloc'd=9658= at 0x4C24724: calloc (vg_replace_malloc.c:368)=9658= by 0xE55A373: IceOpenConnection (in /usr/lib/libICE.so.6.3.0)=9658= at 0x4E38ECB: ? (in /lib/libpthread-2.8.90.so)=9658= by 0x7E00876: ? (in /usr/lib/libsqlite3.so.0.8.6)=9658= Address 0x15dcfefc is 36 bytes inside a block of size 4,104 alloc'd=9658= at 0x4C2694E: malloc (vg_replace_malloc.c:178)=9658= by 0x7DE9CF7: sqlite3_malloc (in /usr/lib/libsqlite3.so.0.8.6)=9658= ERROR SUMMARY: 19 errors from 3 contexts (suppressed: 343 from 3)We have three Memcheck start-up messages, two Memcheck shut-down messages, and two PIDs. Others may disagree, so it would be useful to know if Valgrind users have an opinion on this. And allowing patterns would be useful. You would specify a list of processes, anything not on that list would be traced, anything on the list would not be traced. It would often be useful to be able to trace some of them.An obvious way to do this is with a black-list. Proposal 3: control child tracing via black-listingCurrently you either trace all child processes, or none of them. But -v produces lots of extra stuff that is rarely interesting, so it’s not a good solution.So my second proposal is to always print the invoked command as part of the Valgrind start-up message, like this: =9045= Memcheck, a memory error detector.(We could possibly move the “For more details” message to shut-down, where other, similar messages are shown.)In this case the command has no arguments, but they would be shown if present.This change would make the output of running Valgrind on multi-process programs much easier to run.Another possibility is to also show the parent process’s command, but that is probably overkill. Without that I would have had a much harder time understanding what happened. If I had too choose one, I’d probably pick the latter the former seems less likely to be useful. This incurs a slow-down of about 5x compared to native execution, but allows Valgrind to keep control.So there are two possible kinds of black-list: the “skip you” black-list, and the “skip you and all your descendents” black-list. An alternative is to run the black-listed processes under Nulgrind, the Valgrind tool that adds no instrumentation. It looks like it might match# all command containing the substring "python", but it does not, because# patterns must match the entire command, not just part of it.# Skips all /usr/bin/python and /usr/bin/perl subprocesses multiple# blacklist options are combined, and any process matching any of the-trace-blacklist='/usr/bin/python *' -trace-blacklist='/usr/bin/perl *'One interesting question is this: what exactly does it mean to not trace a process? More specifically, if an untraced process spawns its own children, should we trace them? If we run the process natively (as –trace-children=no currently does for child processes) then any spawned children will not be traced — once Valgrind loses control, it cannot get it back. Traces no children.# Skips all /usr/bin/python subprocesses.# Skips all /usr/bin/python subprocesses invoked with -v.# Matches nothing, ie. (Single quotes are necessary to# protect most patterns from shell interference.)# Matches everything, ie.
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