[BOLT][PAC] Warn about synchronous unwind tables

[bgergely0]

BOLT currently ignores functions with synchronous PAuth DWARF info.
When more than 10% of functions get ignored for inconsistencies, we
should emit a warning to only use asynchronous unwind tables.

See also: #165215

[bgergely0]

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• [BOLT] Fix thread-safety of PointerAuthCFIAnalyzer #165365
• [BOLT][PAC] Warn about synchronous unwind tables #165227 👈 (View in Graphite)
• [BOLT] Rename Pointer Auth DWARF rewriter passes #164622
• [BOLT] Improve DWARF CFI generation for pac-ret binaries #163381
• [BOLT] Simplify RAState helpers (NFCI) #162820
• main

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[llvmbot]

@llvm/pr-subscribers-bolt

Author: Gergely Bálint (bgergely0)

Changes

BOLT currently ignores functions with synchronous PAuth DWARF info.
When more than 10% of functions get ignored for inconsistencies, we
should emit a warning to only use asynchronous unwind tables.

See also: #165215

---

Full diff: https://github.com/llvm/llvm-project/pull/165227.diff

2 Files Affected:

• (modified) bolt/lib/Passes/PointerAuthCFIAnalyzer.cpp (+7-1)
• (added) bolt/test/runtime/AArch64/pacret-synchronous-unwind.cpp (+32)

diff --git a/bolt/lib/Passes/PointerAuthCFIAnalyzer.cpp b/bolt/lib/Passes/PointerAuthCFIAnalyzer.cpp index 2fc5a2fda086a..6bcb5a6bd1801 100644 --- a/bolt/lib/Passes/PointerAuthCFIAnalyzer.cpp +++ b/bolt/lib/Passes/PointerAuthCFIAnalyzer.cpp @@ -130,11 +130,17 @@ Error PointerAuthCFIAnalyzer::runOnFunctions(BinaryContext &BC) { ParallelUtilities::runOnEachFunction( BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, SkipPredicate, "PointerAuthCFIAnalyzer"); + + float IgnoredPercent = (100.0 * FunctionsIgnored) / Total; BC.outs() << "BOLT-INFO: PointerAuthCFIAnalyzer ran on " << Total << " functions. Ignored " << FunctionsIgnored << " functions " - << format("(%.2lf%%)", (100.0 * FunctionsIgnored) / Total) + << format("(%.2lf%%)", IgnoredPercent) << " because of CFI inconsistencies\n"; + if (IgnoredPercent >= 10.0) + BC.outs() << "BOLT-WARNING: PointerAuthCFIAnalyzer only supports " + "asynchronous unwind tables.\n"; + return Error::success(); } diff --git a/bolt/test/runtime/AArch64/pacret-synchronous-unwind.cpp b/bolt/test/runtime/AArch64/pacret-synchronous-unwind.cpp new file mode 100644 index 0000000000000..e90882833323d --- /dev/null +++ b/bolt/test/runtime/AArch64/pacret-synchronous-unwind.cpp @@ -0,0 +1,32 @@ +// Test to demonstrate that functions compiled with synchronous unwind tables +// are ignored by the PointerAuthCFIAnalyzer. +// Exception handling is needed to have _any_ unwind tables, otherwise the +// PointerAuthCFIAnalyzer does not run on these functions, so it does not ignore +// any function. +// +// REQUIRES: system-linux,bolt-runtime +// +// RUN: %clangxx --target=aarch64-unknown-linux-gnu \ +// RUN: -mbranch-protection=pac-ret \ +// RUN: -fno-asynchronous-unwind-tables \ +// RUN: %s -o %t.exe -Wl,-q +// RUN: llvm-bolt %t.exe -o %t.bolt | FileCheck %s --check-prefix=CHECK +// +// CHECK: PointerAuthCFIAnalyzer ran on 3 functions. Ignored +// CHECK-NOT: 0 functions (0.00%) because of CFI inconsistencies +// CHECK-SAME: 1 functions (33.33%) because of CFI inconsistencies +// CHECK-NEXT: PointerAuthCFIAnalyzer only supports asynchronous unwind tables + +#include <cstdio> +#include <stdexcept> + +void foo() { throw std::runtime_error("Exception from foo()."); } + +int main() { + try { + foo(); + } catch (const std::exception &e) { + printf("Exception caught: %s\n", e.what()); + } + return 0; +} 

[bgergely0]

Looks like the code formatting bot is broken, but the patch is formatted locally.

[bgergely0]

As an input binary with sync unwind tables generates many warnings, it made sense to add the verbosity checking in this PR as well.