The SystemTap script fails with "semantic error: conditional branches not supported in DWARF expression" error.

Solution In Progress - Updated -

Issue

  • The SystemTap script fails with error with semantic error.
# stap -v cache-hit-rate.stp
Pass 1: parsed user script and 489 library scripts using 339968virt/138436res/17440shr/122848data kb, in 230usr/50sys/342real ms.
semantic error: conditional branches not supported in DWARF expression [8] at 33 (40: 1, 0): identifier '$count' at /usr/share/systemtap/tapset/linux/vfs.stp:990:18
        dieoffset: 0x48f5751 from /usr/lib/debug/lib/modules/4.18.0-477.27.1.el8_8.x86_64/vmlinux
        source:     bytes_to_read = $count
                                                           ^

semantic error: conditional branches not supported in DWARF expression [8] at 33 (40: 1, 0): identifier '$count' at :990:18
        dieoffset: 0x48f5751 from /usr/lib/debug/lib/modules/4.18.0-477.27.1.el8_8.x86_64/vmlinux
        source:     bytes_to_read = $count
                                                           ^

Pass 2: analyzed script: 6 probes, 31 functions, 6 embeds, 5 globals using 590080virt/389964res/19176shr/372960data kb, in 2490usr/300sys/2817real ms.
Pass 2: analysis failed.  [man error::pass2]

Environment

  • RHEL 8
  • systemtap

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