perf probe: Find fentry mcount fuzzed parameter location
At this point, --fentry (mcount function entry) option for gcc fuzzes the debuginfo variable locations by skipping the mcount instruction offset (on x86, this is a 5 byte call instruction). This makes variable searching fail at the entry of functions which are mcount'ed. e.g.) Available variables at vfs_read @<vfs_read+0> (No matched variables) This patch adds additional location search at the function entry point to solve this issue, which tries to find the earliest address for the variable location. Note that this only works with function parameters (formal parameters) because any local variables should not exist on the function entry address (those are not initialized yet). With this patch, perf probe shows correct parameters if possible; # perf probe --vars vfs_read Available variables at vfs_read @<vfs_read+0> char* buf loff_t* pos size_t count struct file* file Signed-off-by: NMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/20131011071025.15557.13275.stgit@udc4-manage.rcp.hitachi.co.jpSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
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