diff options
author | Shoaib Meenai <smeenai@fb.com> | 2022-04-26 08:51:10 +0300 |
---|---|---|
committer | Shoaib Meenai <smeenai@fb.com> | 2022-04-27 04:48:26 +0300 |
commit | 7cc328600e250ef44f86da34e93fcdd0635339e0 (patch) | |
tree | 31fbe10b5a998d45b7748d7c1b3f1bef3d45345a /lld | |
parent | c15ae0a37dda4a776d974dbe5360707163e34bda (diff) |
[ELF] Prevent LTO stripping of wrapped script-referenced symbols
After 1af25a986069f2ae8c724133fa8649bb795a7925, we stop unconditionally
retaining wrapped symbols, which means that LTO's summary-based global
dead stripping can eliminate them even if they'll be referenced by a
linker script after the wrapping is performed. Mark symbols referenced
in linker scripts as `referenced` in addition to `isUsedInRegularObj`,
so that the wrapping logic correctly sets `referencedAfterWrap` for the
symbols which will be referenced after wrapping, which will prevent LTO
from eliminating them.
An alternative would have been to change the `referencedAfterWrap` logic
to look at `isUsedInRegularObj` in addition to `referenced`, but
`isUsedInRegularObj` is also set in other places (e.g. for the entry
symbol), and it's not clear that we want `referencedAfterWrap` to take
all those places into account, so it seemed better to keep that logic
as-is and instead set `referenced` for linker script-referenced symbols.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D124433
Diffstat (limited to 'lld')
-rw-r--r-- | lld/ELF/Driver.cpp | 7 | ||||
-rw-r--r-- | lld/test/ELF/lto/wrap-script-referenced.ll | 46 |
2 files changed, 51 insertions, 2 deletions
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp index 41620737e1f6..ba24be790186 100644 --- a/lld/ELF/Driver.cpp +++ b/lld/ELF/Driver.cpp @@ -2463,8 +2463,11 @@ void LinkerDriver::link(opt::InputArgList &args) { // Some symbols (such as __ehdr_start) are defined lazily only when there // are undefined symbols for them, so we add these to trigger that logic. - for (StringRef name : script->referencedSymbols) - addUnusedUndefined(name)->isUsedInRegularObj = true; + for (StringRef name : script->referencedSymbols) { + Symbol *sym = addUnusedUndefined(name); + sym->isUsedInRegularObj = true; + sym->referenced = true; + } // Prevent LTO from removing any definition referenced by -u. for (StringRef name : config->undefined) diff --git a/lld/test/ELF/lto/wrap-script-referenced.ll b/lld/test/ELF/lto/wrap-script-referenced.ll new file mode 100644 index 000000000000..8c2f5e23f46c --- /dev/null +++ b/lld/test/ELF/lto/wrap-script-referenced.ll @@ -0,0 +1,46 @@ +;; Verify that the target of a wrap is kept by LTO's summary-based global dead +;; stripping if the original symbol is referenced by a linker script or --defsym + +; REQUIRES: x86 +; RUN: rm -rf %t && split-file %s %t + +;; We need a module summary to trigger summary-based global stripping +; RUN: opt -module-summary -o %t/foo.bc %t/foo.ll +; RUN: echo 'alias = __real_foo;' > %t/alias.script +; RUN: ld.lld -shared -o %t/libalias_foo.so %t/foo.bc %t/alias.script --wrap foo +; RUN: llvm-readelf --syms %t/libalias_foo.so | FileCheck --check-prefix=FOO %s + +; FOO: Symbol table '.symtab' contains +; FOO-DAG: [[#]]: [[#%.16x,FOO_VAL:]] 1 FUNC LOCAL HIDDEN [[#]] foo +; FOO-DAG: [[#]]: [[#FOO_VAL]] 0 FUNC GLOBAL DEFAULT [[#]] alias + +; RUN: opt -module-summary -o %t/wrap_foo.bc %t/wrap_foo.ll +; RUN: ld.lld -shared -o %t/libalias_wrap_foo.so %t/wrap_foo.bc --wrap foo --defsym=alias=foo +; RUN: llvm-readelf --syms %t/libalias_wrap_foo.so | FileCheck --check-prefix=WRAP-FOO %s + +; WRAP-FOO: Symbol table '.symtab' contains +; WRAP-FOO-DAG: [[#]]: [[#%.16x,WRAP_FOO_VAL:]] 1 FUNC LOCAL HIDDEN [[#]] __wrap_foo +; WRAP-FOO-DAG: [[#]]: [[#WRAP_FOO_VAL]] 0 FUNC GLOBAL DEFAULT [[#]] alias + +;--- foo.ll +target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-unknown-linux-gnu" +define hidden void @foo() { + ret void +} + +;; We need a live root to trigger summary-based global stripping +define dso_local void @bar() { + ret void +} + +;--- wrap_foo.ll +target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-unknown-linux-gnu" +define hidden void @__wrap_foo() { + ret void +} + +define dso_local void @bar() { + ret void +} |