[sancov] Introduce optional callback for stack-depth tracking (#138323)

Normally -fsanitize-coverage=stack-depth inserts inline arithmetic to
update thread_local __sancov_lowest_stack. To support stack depth
tracking in the Linux kernel, which does not implement traditional
thread_local storage, provide the option to call a function instead.

This matches the existing "stackleak" implementation that is supported
in Linux via a GCC plugin. To make this coverage more performant, a
minimum estimated stack depth can be chosen to enable the callback mode,
skipping instrumentation of functions with smaller stacks.

With -fsanitize-coverage-stack-depth-callback-min set greater than 0,
the __sanitize_cov_stack_depth() callback will be injected when the
estimated stack depth is greater than or equal to the given minimum.

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index c9ceb49..42c5937 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -255,6 +255,7 @@ getSancovOptsFromCGOpts(const CodeGenOptions &CGOpts) {
   Opts.InlineBoolFlag = CGOpts.SanitizeCoverageInlineBoolFlag;
   Opts.PCTable = CGOpts.SanitizeCoveragePCTable;
   Opts.StackDepth = CGOpts.SanitizeCoverageStackDepth;
+  Opts.StackDepthCallbackMin = CGOpts.SanitizeCoverageStackDepthCallbackMin;
   Opts.TraceLoads = CGOpts.SanitizeCoverageTraceLoads;
   Opts.TraceStores = CGOpts.SanitizeCoverageTraceStores;
   Opts.CollectControlFlow = CGOpts.SanitizeCoverageControlFlow;