Messages in this thread | | | Date | Thu, 6 Aug 2009 05:43:25 +0200 | From | Ingo Molnar <> | Subject | Re: ftrace scripts and make V=1 |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> Well we tracked it down and it is powerpc64 specific. > > Seems that in drivers/hwmon/lm93.c there's a function called: > > LM93_IN_FROM_REG() > > But PPC64 has function descriptors and the real function names (the ones > you see in objdump) start with a '.'. Thus this in objdump you have: > > Disassembly of section .text: > > 0000000000000000 <.LM93_IN_FROM_REG>: > 0: 7c 08 02 a6 mflr r0 > 4: fb 81 ff e0 std r28,-32(r1) > > > The function name used is .LM93_IN_FROM_REG. But gcc considers > symbols that start with ".L" as a special symbol that is used > inside the assembly stage. > > The nm passed into recordmcount uses the --synthetic option which > shows the ".L" symbols (my runs outside of the build did not > include the --synthetic option, so my older patch worked). We see > the function as a local. > > Now to capture all the locations that use "mcount" we need to have > a reference to link into the object file a list of mcount callers. > We need a reference that will not disappear. We try to use a > global function and if that does not work, we use a local function > as a reference. But to relink the section back into the object, we > need to make it global. In this case, we run objcopy using > --globalize-symbol and --localize-symbol to convert the symbol > into a global symbol, link the mcount list, then convert it back > to a local symbol. > > This works great except for this case. .L* symbols can not be > converted into a global symbol, and the mcount section referencing > it will remain unresolved. > > Try this patch and see if it fixes your issue. > > Thanks! > > -- Steve > > diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl > index d29baa2..4889c44 100755 > --- a/scripts/recordmcount.pl > +++ b/scripts/recordmcount.pl > @@ -414,7 +414,10 @@ while (<IN>) { > $offset = hex $1; > } else { > # if we already have a function, and this is weak, skip it > - if (!defined($ref_func) && !defined($weak{$text})) { > + if (!defined($ref_func) && !defined($weak{$text}) && > + # PPC64 can have symbols that start with .L and > + # gcc considers these special. Don't use them! > + $text !~ /^\.L/) { > $ref_func = $text; > $offset = hex $1; > }
Ah, indeed. I'm wondering whether also emitting a build warning would be useful - just in the (admittedly unlikely) case of someone wondering about why LM93_IN_FROM_REG does not show up in function traces.
Ingo
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