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A file-local symbol which ThinLTO has to make visible is renamed helper.llvm.<hash>. With two such helpers in one link, the original and the patched object hold two each, all four spelled differently, and demangling gives "helper" for every one of them -- so the name alone cannot say which corresponds to which. Three translation units, two with a static helper of the same name and a third calling into both, which is what forces the promotion. Only one helper changes: paired correctly that means exactly one is cloned, and paired the wrong way round the other is, or both are. Had both bodies changed, both would be cloned either way and the test would prove nothing -- which is how the first version of this was written. The outcome is asserted, not the machinery. With the clang tested here the pairing survives disabling the .llvm.<hash> suffix map and stubbing out llvm_suffix() entirely, so no single-line sabotage distinguishes it; the tiered matcher this case was written for is not needed for this shape. The test says so rather than implying otherwise. Assisted-by: Claude:claude-opus-4 Based-on-test-by: Joe Lawrence <joe.lawrence@redhat.com> Assisted-by: Claude:claude-opus-5 Signed-off-by: Song Liu <song@kernel.org> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://patch.msgid.link/20260916184351.2720310-59-song@kernel.org
78 lines
3.1 KiB
Bash
Executable File
78 lines
3.1 KiB
Bash
Executable File
#!/bin/bash
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# SPDX-License-Identifier: GPL-2.0
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#
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# Two ThinLTO-promoted symbols sharing a demangled name must be paired up
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# correctly.
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#
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# A file-local symbol which ThinLTO has to make visible is renamed
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# helper.llvm.<hash>. With two such helpers in one link the original and the
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# patched object hold two each, all four spelled differently, and demangling
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# gives "helper" for all of them -- so the name is not enough to say which
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# corresponds to which.
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#
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# Getting it wrong is silent and specific: the patch is built against the wrong
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# body, so one call site gets the other helper's arithmetic. Nothing fails to
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# build and nothing fails to load.
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#
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# test-thinlto-local covers the unambiguous case, one promoted symbol whose
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# hash moved. This is the case where demangling alone is not an answer.
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#
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# The outcome is asserted, not the machinery: with the clang tested here the
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# pairing succeeds even with the .llvm.<hash> suffix map disabled and with
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# llvm_suffix() stubbed out, so no single-line sabotage distinguishes it. The
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# tiered matcher this case was written for is not needed for this shape.
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#
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# Covers the same ground as corpus/x86_64-llvm-thinlto/
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# thin-lto-demangled-ambiguity and thin-lto-demangled-global-match in Joe
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# Lawrence's klp-build unit test corpus.
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. "$(dirname "$0")/../lib.sh"
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setup
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clang_only "ThinLTO requires clang"
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find_thinlto_toolchain ||
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probe_skip "no matching clang/lld pair for a ThinLTO link; set THIN_LD to one"
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build_thinlto() # $1 output object, $2 extra flags
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{
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local t
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for t in "" -DTU_B -DTU_C; do
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$THIN_CC -flto=thin -O2 -ffunction-sections -fdata-sections \
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$2 $t -c "$FIXTURES_DIR/thinlto_ambiguity.c" \
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-o "$workdir/tu$t.o" 2>/dev/null || return 1
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done
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"$THIN_LD" -r "$workdir/tu.o" "$workdir/tu-DTU_B.o" "$workdir/tu-DTU_C.o" \
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-o "$1" 2>/dev/null || return 1
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}
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build_thinlto "$workdir/orig.o" "" ||
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probe_skip "ThinLTO build failed ($THIN_CC, $THIN_LD)"
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build_thinlto "$workdir/patched.o" -DPATCHED ||
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probe_skip "ThinLTO build failed ($THIN_CC, $THIN_LD)"
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# The premise: two promoted helpers per object, and exactly one of them kept
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# its hash -- the one the patch did not touch. Without that there is nothing
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# to disambiguate.
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orig_syms="$(in_symbols orig.o | grep -oE 'helper\.llvm\.[0-9]+' | sort -u)"
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new_syms="$( in_symbols patched.o | grep -oE 'helper\.llvm\.[0-9]+' | sort -u)"
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[ "$(echo "$orig_syms" | wc -l)" = 2 ] && [ "$(echo "$new_syms" | wc -l)" = 2 ] ||
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probe_skip "ThinLTO did not promote two distinct helpers here"
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kept="$(comm -12 <(echo "$orig_syms") <(echo "$new_syms"))"
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moved="$(comm -13 <(echo "$orig_syms") <(echo "$new_syms"))"
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[ "$(echo "$kept" | wc -w)" = 1 ] && [ "$(echo "$moved" | wc -w)" = 1 ] ||
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probe_skip "expected one helper to keep its hash and one to move"
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run_diff
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# Exactly one helper is cloned, and it is the one whose body changed. Cloning
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# the other, or both, is what a wrong pairing looks like.
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assert_not_patched "$kept"
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n="$(out_sections | grep -cE '[[:space:]]\.text\.helper\.llvm\.[0-9]+[[:space:]]')"
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[ "$n" = 1 ] ||
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fail "expected 1 cloned helper, found $n"
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pass "ThinLTO helpers sharing a demangled name paired up correctly"
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