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fix(test): stop -O3 tail-calling away the return-address trampolines #819

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Merged
rkennke merged 2 commits into from
Sep 25, 2026
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fix(test): stop -O3 tail-calling away the return-address trampolines #819

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269ba26
fix(test): stop -O3 tail-calling away the return-address trampolines
rkennke Sep 24, 2026
8b500d4
test: drop the pre-call half of the tail-call guard
rkennke Sep 24, 2026
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17 changes: 12 additions & 5 deletions ddprof-lib/src/test/cpp/returnAddressAttribution_ut.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -856,10 +856,16 @@ extern "C" void prof_ra_cfi_collect(void) {
// Named trampoline so Test 3's "caller of the boundary frame" is a specific,
// symbolizable function rather than the test body itself.
extern "C" __attribute__((noinline)) void prof_ra_cfi_trampoline(void) {
// volatile to defeat tail-call/inlining folding this frame away.
volatile int guard = 1;
(void)guard;
prof_ra_cfi_caller();
// noinline only stops this function being inlined into its caller; at -O3
// the call above would still become a tail jump, erasing this frame at
// runtime. A volatile store after the call leaves the compiler something
// to do on return, so the call cannot be a tail call and the frame
// survives for the walker to attribute against. A volatile store *before*
// the call does not work -- the compiler emits it and then tears the frame
// down anyway.
volatile int sink = 0;
(void)sink;
}

#endif // __x86_64__ || __aarch64__
Expand Down Expand Up @@ -1027,9 +1033,10 @@ extern "C" void prof_ra_plt_collect(void) {
}

extern "C" __attribute__((noinline)) void prof_ra_plt_trampoline(void) {
volatile int guard = 1;
(void)guard;
prof_ra_plt_caller();
// Same tail-call guard as prof_ra_cfi_trampoline above.
volatile int sink = 0;
(void)sink;
}

#endif // __x86_64__ || __aarch64__
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