[lld] 2325788 - [ELF] Add --warn-backrefs-exclude=<glob>
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 20 07:52:23 PDT 2020
Author: Fangrui Song
Date: 2020-04-20T07:52:15-07:00
New Revision: 232578804ab89ac1aa7e2e0f32a5980971dfaefb
URL: https://github.com/llvm/llvm-project/commit/232578804ab89ac1aa7e2e0f32a5980971dfaefb
DIFF: https://github.com/llvm/llvm-project/commit/232578804ab89ac1aa7e2e0f32a5980971dfaefb.diff
LOG: [ELF] Add --warn-backrefs-exclude=<glob>
D77522 changed --warn-backrefs to not warn for linking sandwich
problems (-ldef1 -lref -ldef2). This removed lots of false positives.
However, glibc still has some problems. libc.a defines some symbols
which are normally in libm.a and libpthread.a, e.g. __isnanl/raise.
For a linking order `-lm -lpthread -lc`, I have seen:
```
// different resolutions: GNU ld/gold select libc.a(s_isnan.o) as the definition
backward reference detected: __isnanl in libc.a(printf_fp.o) refers to libm.a(m_isnanl.o)
// different resolutions: GNU ld/gold select libc.a(raise.o) as the definition
backward reference detected: raise in libc.a(abort.o) refers to libpthread.a(pt-raise.o)
```
To facilitate deployment of --warn-backrefs, add --warn-backrefs-exclude= so that
certain known issues (which may be impractical to fix) can be whitelisted.
Deliberate choices:
* Not a comma-separated list (`--warn-backrefs-exclude=liba.a,libb.a`).
-Wl, splits the argument at commas, so we cannot use commas.
--export-dynamic-symbol is similar.
* Not in the style of `--warn-backrefs='*' --warn-backrefs=-liba.a`.
We just need exclusion, not inclusion. For easier build system
integration, we should avoid order dependency. With the current
scheme, we enable --warn-backrefs, and indivial libraries can add
--warn-backrefs-exclude=<glob> to their LDFLAGS.
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D77512
Added:
Modified:
lld/ELF/Config.h
lld/ELF/Driver.cpp
lld/ELF/Options.td
lld/ELF/Symbols.cpp
lld/docs/ld.lld.1
lld/test/ELF/warn-backrefs.s
Removed:
################################################################################
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 70ef86239aa2..e01a16b81023 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -17,6 +17,7 @@
#include "llvm/Support/CachePruning.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/Endian.h"
+#include "llvm/Support/GlobPattern.h"
#include <atomic>
#include <vector>
@@ -201,6 +202,7 @@ struct Configuration {
bool unique;
bool useAndroidRelrTags = false;
bool warnBackrefs;
+ std::vector<llvm::GlobPattern> warnBackrefsExclude;
bool warnCommon;
bool warnIfuncTextrel;
bool warnMissingEntry;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 35153a1bff8b..b074ae68d012 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1148,6 +1148,14 @@ static void readConfigs(opt::InputArgList &args) {
{s, /*isExternCpp=*/false, /*hasWildcard=*/false});
}
+ for (opt::Arg *arg : args.filtered(OPT_warn_backrefs_exclude)) {
+ StringRef pattern(arg->getValue());
+ if (Expected<GlobPattern> pat = GlobPattern::create(pattern))
+ config->warnBackrefsExclude.push_back(std::move(*pat));
+ else
+ error(arg->getSpelling() + ": " + toString(pat.takeError()));
+ }
+
// Parses -dynamic-list and -export-dynamic-symbol. They make some
// symbols private. Note that -export-dynamic takes precedence over them
// as it says all symbols should be exported.
diff --git a/lld/ELF/Options.td b/lld/ELF/Options.td
index 8dd525130a70..799707af49fa 100644
--- a/lld/ELF/Options.td
+++ b/lld/ELF/Options.td
@@ -403,6 +403,12 @@ defm warn_backrefs: B<"warn-backrefs",
"Warn about backward symbol references to fetch archive members",
"Do not warn about backward symbol references to fetch archive members (default)">;
+defm warn_backrefs_exclude
+ : Eq<"warn-backrefs-exclude",
+ "Glob describing an archive (or an object file within --start-lib) "
+ "which should be ignored for --warn-backrefs.">,
+ MetaVarName<"<glob>">;
+
defm warn_common: B<"warn-common",
"Warn about duplicate common symbols",
"Do not warn about duplicate common symbols (default)">;
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index fe1c2cacd310..235ebe4560ff 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -16,6 +16,7 @@
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include <cstring>
@@ -514,6 +515,17 @@ void Symbol::resolveUndefined(const Undefined &other) {
// group assignment rule simulates the traditional linker's semantics.
bool backref = config->warnBackrefs && other.file &&
file->groupId < other.file->groupId;
+ if (backref) {
+ // Some libraries have known problems and can cause noise. Filter them out
+ // with --warn-backrefs-exclude=.
+ StringRef name =
+ !file->archiveName.empty() ? file->archiveName : file->getName();
+ for (const llvm::GlobPattern &pat : config->warnBackrefsExclude)
+ if (pat.match(name)) {
+ backref = false;
+ break;
+ }
+ }
fetch();
// We don't report backward references to weak symbols as they can be
diff --git a/lld/docs/ld.lld.1 b/lld/docs/ld.lld.1
index 7af9a16e83f9..1d55cf052c9b 100644
--- a/lld/docs/ld.lld.1
+++ b/lld/docs/ld.lld.1
@@ -574,6 +574,10 @@ Read version script from
Warn about reverse or cyclic dependencies to or between static archives.
This can be used to ensure linker invocation remains compatible with
traditional Unix-like linkers.
+.It Fl -warn-backrefs-exclude Ns = Ns Ar glob
+Glob describing an archive (or an object file within --start-lib)
+which should be ignored for
+.Fl -warn-backrefs
.It Fl -warn-common
Warn about duplicate common symbols.
.It Fl -warn-ifunc-textrel
diff --git a/lld/test/ELF/warn-backrefs.s b/lld/test/ELF/warn-backrefs.s
index 5dec458232ee..6308c57e6dc7 100644
--- a/lld/test/ELF/warn-backrefs.s
+++ b/lld/test/ELF/warn-backrefs.s
@@ -15,9 +15,16 @@
# RUN: ld.lld --fatal-warnings --warn-backrefs %t1.lds -o /dev/null
## A backward reference from %t1.o to %t2.a
+## Warn unless the archive is excluded by --warn-backrefs-exclude
# RUN: ld.lld --fatal-warnings %t2.a %t1.o -o /dev/null
# RUN: ld.lld --warn-backrefs %t2.a %t1.o -o /dev/null 2>&1 | FileCheck %s
# RUN: ld.lld --warn-backrefs %t2.a '-(' %t1.o '-)' -o /dev/null 2>&1 | FileCheck %s
+# RUN: ld.lld --warn-backrefs --warn-backrefs-exclude='*3.a' %t2.a %t1.o -o /dev/null 2>&1 | FileCheck %s
+# RUN: ld.lld --fatal-warnings --warn-backrefs --warn-backrefs-exclude='*2.a' %t2.a %t1.o -o /dev/null
+# RUN: ld.lld --fatal-warnings --warn-backrefs --warn-backrefs-exclude '*2.a' \
+# RUN: --warn-backrefs-exclude not_exist %t2.a %t1.o -o /dev/null
+## Without --warn-backrefs, --warn-backrefs-exclude is ignored.
+# RUN: ld.lld --fatal-warnings --warn-backrefs-exclude=not_exist %t2.a %t1.o -o /dev/null
## Placing the definition and the backward reference in a group can suppress the warning.
# RUN: echo 'GROUP("%t2.a" "%t1.o")' > %t2.lds
@@ -28,14 +35,17 @@
# RUN: echo 'GROUP("%t2.a")' > %t3.lds
# RUN: ld.lld --warn-backrefs %t3.lds %t1.o -o /dev/null 2>&1 | FileCheck %s
# RUN: ld.lld --fatal-warnings --warn-backrefs '-(' %t3.lds %t1.o '-)' -o /dev/null
+# RUN: ld.lld --fatal-warnings --warn-backrefs --warn-backrefs-exclude='*2.a' -o /dev/null %t3.lds %t1.o
## If a lazy definition appears after the backward reference, don't warn.
# RUN: ld.lld --fatal-warnings --warn-backrefs %t3.lds %t1.o %t3.lds -o /dev/null
# CHECK: warning: backward reference detected: foo in {{.*}}1.o refers to {{.*}}2.a
## A backward reference from %t1.o to %t2.o
+## --warn-backrefs-exclude= applies to --start-lib covered object files.
# RUN: ld.lld --warn-backrefs --start-lib %t2.o --end-lib %t1.o -o /dev/null 2>&1 | \
# RUN: FileCheck --check-prefix=OBJECT %s
+# RUN: ld.lld --fatal-warnings --warn-backrefs --warn-backrefs-exclude=%/t2.o --start-lib %/t2.o --end-lib %t1.o -o /dev/null
## If a lazy definition appears after the backward reference, don't warn.
# RUN: ld.lld --fatal-warnings --warn-backrefs --start-lib %t2.o --end-lib %t1.o --start-lib %t2.o --end-lib -o /dev/null
@@ -68,6 +78,9 @@
## In GNU gold, --export-dynamic-symbol does not make a backward reference.
# RUN: ld.lld --fatal-warnings --warn-backrefs --export-dynamic-symbol foo %t2.a %t1.o -o /dev/null
+# RUN: not ld.lld --warn-backrefs-exclude='[' 2>&1 | FileCheck --check-prefix=INVALID %s
+# INVALID: error: --warn-backrefs-exclude: invalid glob pattern: [
+
.globl _start, foo
_start:
call foo
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