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Improve attaching to uprobes with size 0 #2562

Merged
merged 1 commit into from
Apr 14, 2023
Merged

Improve attaching to uprobes with size 0 #2562

merged 1 commit into from
Apr 14, 2023

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viktormalik
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@viktormalik viktormalik commented Apr 12, 2023 •
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Compilers do not set symbol size in the .symtab ELF section for some of their generated symbols (e.g. _init and _fini). This causes problems when attaching to these as we are not able to check offset.

This commit enables attachment to such functions if the offset is 0 and --unsafe is used. For other cases, appropriate error/warning is shown.

In total, there are multiple cases covered:

  • unsafe is on: allow attachment to symbols with size 0,
  • unsafe is off, attaching to multiple probes: skip symbols with size 0 and show a warning,
  • unsafe is off, attaching to a single probe: fail and show an error.

Added runtime tests for cases 1 and 3 but disabled them on embedded alpine builds since the _init symbol seems to have non-zero size there.

Fixes #2552, fixes #940.

Checklist
  • Language changes are updated in man/adoc/bpftrace.adoc and if needed in docs/reference_guide.md
  • User-visible and non-trivial changes updated in CHANGELOG.md
  • The new behaviour is covered by tests

@viktormalik viktormalik requested review from ajor, danobi and fbs as code owners April 12, 2023 08:42
@viktormalik
Improve attaching to uprobes with size 0
9fcb098 
Compilers do not set symbol size in the .symtab ELF section for some of
their generated symbols (e.g. _init and _fini). This causes problems
when attaching to these as we are not able to check offset.

This commit enables attachment to such functions if the offset is 0 and
--unsafe is used. For other cases, appropriate error/warning is shown.

In total, there are multiple cases covered:
- unsafe is on: allow attachment to symbols with size 0,
- unsafe is off, attaching to multiple probes: skip symbols with size 0
  and show a warning,
- unsafe is off, attaching to a single probe: fail and show an error.

Added runtime tests for cases 1 and 3 but disabled them on embedded
alpine builds since the _init symbol seems to have non-zero size there.
@viktormalik viktormalik mentioned this pull request Apr 13, 2023
Closed
@viktormalik viktormalik merged commit 31aa8bf into bpftrace:master Apr 14, 2023
@viktormalik viktormalik deleted the uprobe-zero-size branch April 20, 2023 05:56
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@dxuuu dxuuu dxuuu approved these changes

@danobi danobi danobi approved these changes

@ajor ajor Awaiting requested review from ajor ajor is a code owner

@fbs fbs Awaiting requested review from fbs fbs is a code owner

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Successfully merging this pull request may close these issues.

uprobes: trying to trace all functions of a userspace program using '*' returns an error "Offset outside the function bounds" Can't attach to uprobes if .size information is missing
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@viktormalik @danobi @dxuuu