Merge pull request #39 from aalexand/master

Handle PowerPC64 kernel mapping in getBase().

internal/elfexec/elfexec.go

 // use the address of the _stext symbol as the mmap start.  _stext
 // offset can be obtained with `nm vmlinux | grep _stext`
 func GetBase(fh *elf.FileHeader, loadSegment *elf.ProgHeader, stextOffset *uint64, start, limit, offset uint64) (uint64, error) {
-	const pageSize = 4096
+	const (
+		pageSize = 4096
+		// PAGE_OFFSET for PowerPC64, see arch/powerpc/Kconfig in the kernel sources.
+		pageOffsetPpc64 = 0xc000000000000000
+	)
 
 	if start == 0 && offset == 0 &&
 		(limit == ^uint64(0) || limit == 0) {
 		if loadSegment.Vaddr == start-offset {
 			return offset, nil
 		}
-		if start > loadSegment.Vaddr && limit > start && offset == 0 {
+		if start >= loadSegment.Vaddr && limit > start && (offset == 0 || offset == pageOffsetPpc64) {
 			// Some kernels look like:
 			//       VADDR=0xffffffff80200000
 			// stextOffset=0xffffffff80200198
 			//       Start=0xffffffff83200000
 			//       Limit=0xffffffff84200000
-			//      Offset=0
+			//      Offset=0 (0xc000000000000000 for PowerPC64)
 			// So the base should be:
 			if stextOffset != nil && (start%pageSize) == (*stextOffset%pageSize) {
 				// perf uses the address of _stext as start.  Some tools may

internal/elfexec/elfexec_test.go

 	kernelHeader := &elf.ProgHeader{
 		Vaddr: 0xffffffff81000000,
 	}
+	ppc64KernelHeader := &elf.ProgHeader{
+		Vaddr: 0xc000000000000000,
+	}
 
 	testcases := []struct {
 		label                string
 		{"exec offset 2", fhExec, lsOffset, nil, 0x200000, 0x600000, 0, 0, false},
 		{"exec nomap", fhExec, nil, nil, 0, 0, 0, 0, false},
 		{"exec kernel", fhExec, kernelHeader, uint64p(0xffffffff81000198), 0xffffffff82000198, 0xffffffff83000198, 0, 0x1000000, false},
+		{"exec PPC64 kernel", fhExec, ppc64KernelHeader, uint64p(0xc000000000000000), 0xc000000000000000, 0xd00000001a730000, 0xc000000000000000, 0x0, false},
 		{"exec chromeos kernel", fhExec, kernelHeader, uint64p(0xffffffff81000198), 0, 0x10197, 0, 0x7efffe68, false},
 		{"exec chromeos kernel 2", fhExec, kernelHeader, uint64p(0xffffffff81000198), 0, 0x10198, 0, 0x7efffe68, false},
 		{"exec chromeos kernel 3", fhExec, kernelHeader, uint64p(0xffffffff81000198), 0x198, 0x100000, 0, 0x7f000000, false},