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ELF: Synthesize R_RISCV_ALIGN at input section start #5

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@MaskRay MaskRay commented Jul 31, 2025

@MaskRay MaskRay mentioned this pull request Jul 31, 2025
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@MaskRay MaskRay force-pushed the lld-riscv-align branch 4 times, most recently from 01cc246 to 4298172 Compare July 31, 2025 08:12
@MaskRay
ELF: Synthesize R_RISCV_ALIGN at input section start
fabd55d 
Without linker relaxation enabled for a particular relocatable file or
section (e.g., using .option norelax), the assembler will not generate
R_RISCV_ALIGN relocations for alignment directives. This becomes
problematic in a two-stage linking process:

```
ld -r a.o b.o -o ab.o
// b.o is norelax. Its alignment information is lost in ab.o.
ld ab.o -o ab
```

When ab.o is linked into an executable, the preceding relaxed section
(a.o's content) might shrink. Since there's no R_RISCV_ALIGN relocation
in b.o for the linker to act upon, the `.word 0x3a393837` data in b.o
may end up unaligned in the final executable.

To address the issue, this patch inserts NOP bytes and synthesizes an
R_RISCV_ALIGN relocation at the beginning of a text section when the
alignment >= 4.

For simplicity, when RVC is disabled, we synthesize an ALIGN relocation
(addend: 2) for a 4-byte aligned section, allowing the linker to trim
the excess 2 bytes.

See also https://sourceware.org/bugzilla/show_bug.cgi?id=33236
@MaskRay
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MaskRay commented Aug 9, 2025

This is a draft o llvm#151639 , which has been merged

@MaskRay MaskRay closed this Aug 9, 2025
MaskRay pushed a commit that referenced this pull request Aug 15, 2025
@cs01
[lldb] refactor PlatformAndroid and make threadsafe (llvm#145382)
bcb48aa 
## Problem

When the new setting

```
set target.parallel-module-load true
```
was added, lldb began fetching modules from the devices from multiple
threads simultaneously. This caused crashes of lldb when debugging on
android devices.

The top of the stack in the crash look something like this:
```
#0 0x0000555aaf2b27fe llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/llvm/bin/lldb-dap+0xb87fe)
 #1 0x0000555aaf2b0a99 llvm::sys::RunSignalHandlers() (/opt/llvm/bin/lldb-dap+0xb6a99)
 #2 0x0000555aaf2b2fda SignalHandler(int, siginfo_t*, void*) (/opt/llvm/bin/lldb-dap+0xb8fda)
 #3 0x00007f9c02444560 __restore_rt /home/engshare/third-party2/glibc/2.34/src/glibc-2.34/signal/../sysdeps/unix/sysv/linux/libc_sigaction.c:13:0
 #4 0x00007f9c04ea7707 lldb_private::ConnectionFileDescriptor::Disconnect(lldb_private::Status*) (usr/bin/../lib/liblldb.so.15+0x22a7707)
 #5 0x00007f9c04ea5b41 lldb_private::ConnectionFileDescriptor::~ConnectionFileDescriptor() (usr/bin/../lib/liblldb.so.15+0x22a5b41)
 llvm#6 0x00007f9c04ea5c1e lldb_private::ConnectionFileDescriptor::~ConnectionFileDescriptor() (usr/bin/../lib/liblldb.so.15+0x22a5c1e)
 llvm#7 0x00007f9c052916ff lldb_private::platform_android::AdbClient::SyncService::Stat(lldb_private::FileSpec const&, unsigned int&, unsigned int&, unsigned int&) (usr/bin/../lib/liblldb.so.15+0x26916ff)
 llvm#8 0x00007f9c0528b9dc lldb_private::platform_android::PlatformAndroid::GetFile(lldb_private::FileSpec const&, lldb_private::FileSpec const&) (usr/bin/../lib/liblldb.so.15+0x268b9dc)
```
Our workaround was to set `set target.parallel-module-load ` to `false`
to avoid the crash.

## Background

PlatformAndroid creates two different classes with one stateful adb
connection shared between the two -- one through AdbClient and another
through AdbClient::SyncService. The connection management and state is
complex, and seems to be responsible for the segfault we are seeing. The
AdbClient code resets these connections at times, and re-establishes
connections if they are not active. Similarly, PlatformAndroid caches
its SyncService, which uses an AdbClient class, but the SyncService puts
its connection into a different 'sync' state that is incompatible with a
standard connection.

## Changes in this diff

* This diff refactors the code to (hopefully) have clearer ownership of
the connection, clearer separation of AdbClient and SyncService by
making a new class for clearer separations of concerns, called
AdbSyncService.
* New unit tests are added
* Additional logs were added (see
llvm#145382 (comment)
for details)
MaskRay pushed a commit that referenced this pull request Aug 15, 2025
@sahas3
[mlir][tosa] Don't fold mul with zero lhs/rhs if resulting type is dy…
8432f24 
…namic (llvm#153420)

Canonicalizing the following IR:

```
func.func @mul_zero_dynamic_nofold(%arg0: tensor<?x17xf32>) -> tensor<?x17xf32> {
  %0 = "tosa.const"() <{values = dense<0.000000e+00> : tensor<1x1xf32>}> : () -> tensor<1x1xf32>
  %1 = "tosa.const"() <{values = dense<0> : tensor<1xi8>}> : () -> tensor<1xi8>
  %2 = tosa.mul %arg0, %0, %1 : (tensor<?x17xf32>, tensor<1x1xf32>, tensor<1xi8>) -> tensor<?x17xf32>
  return %2 : tensor<?x17xf32>
}
```

resulted in a crash

```
#0 0x000056513187e8db backtrace (./build-release/bin/mlir-opt+0x9d698db)                                                                                                                                                                                                                                                                                                                   
 #1 0x0000565131b17737 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/llvm/lib/Support/Unix/Signals.inc:838:8                                                                                                                                                                                                                
 #2 0x0000565131b187f3 PrintStackTraceSignalHandler(void*) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/llvm/lib/Support/Unix/Signals.inc:918:1                                                                                                                                                                                                                                
 #3 0x0000565131b18c30 llvm::sys::RunSignalHandlers() /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/llvm/lib/Support/Signals.cpp:105:18                                                                                                                                                                                                                                         
 #4 0x0000565131b18c30 SignalHandler(int, siginfo_t*, void*) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/llvm/lib/Support/Unix/Signals.inc:409:3                                                                                                                                                                                                                              
 #5 0x00007f2e4165b050 (/lib/x86_64-linux-gnu/libc.so.6+0x3c050)                                                                                                                                                                                                                                                                                                                            
 llvm#6 0x00007f2e416a9eec __pthread_kill_implementation ./nptl/pthread_kill.c:44:76                                                                                                                                                                                                                                                                                                            
 llvm#7 0x00007f2e4165afb2 raise ./signal/../sysdeps/posix/raise.c:27:6                                                                                                                                                                                                                                                                                                                         
 llvm#8 0x00007f2e41645472 abort ./stdlib/abort.c:81:7                                                                                                                                                                                                                                                                                                                                          
 llvm#9 0x00007f2e41645395 _nl_load_domain ./intl/loadmsgcat.c:1177:9                                                                                                                                                                                                                                                                                                                           
llvm#10 0x00007f2e41653ec2 (/lib/x86_64-linux-gnu/libc.so.6+0x34ec2)                                                                                                                                                                                                                                                                                                                            
llvm#11 0x00005651443ec4ba mlir::DenseIntOrFPElementsAttr::getRaw(mlir::ShapedType, llvm::ArrayRef<char>) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/mlir/lib/IR/BuiltinAttributes.cpp:1361:3                                                                                                                                                                                    
llvm#12 0x00005651443f1209 mlir::DenseElementsAttr::resizeSplat(mlir::ShapedType) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/mlir/lib/IR/BuiltinAttributes.cpp:0:10                                                                                                                                                                                                              
llvm#13 0x000056513f76f2b6 mlir::tosa::MulOp::fold(mlir::tosa::MulOpGenericAdaptor<llvm::ArrayRef<mlir::Attribute>>) /local-ssd/sayans/Softwares/llvm-repo/llvm-project-latest/mlir/lib/Dialect/Tosa/IR/TosaCanonicalizations.cpp:0:0
```

from the folder for `tosa::mul` since the zero value was being reshaped
to `?x17` size which isn't supported. AFAIK, `tosa.const` requires all
dimensions to be static. So in this case, the fix is to not to fold the
op.
MaskRay pushed a commit that referenced this pull request Aug 24, 2025
@jschwartzentruber
[compiler-rt] Fix frame numbering for unparsable frames. (llvm#148278)
b1306da 
This can happen when JIT code is run, and we can't symbolize those
frames, but they should remain numbered in the stack. An example
spidermonkey trace:

```
    #0 0x564ac90fb80f  (/builds/worker/dist/bin/js+0x240e80f) (BuildId: 5d053c76aad4cfbd08259f8832e7ac78bbeeab58)
    #1 0x564ac9223a64  (/builds/worker/dist/bin/js+0x2536a64) (BuildId: 5d053c76aad4cfbd08259f8832e7ac78bbeeab58)
    #2 0x564ac922316f  (/builds/worker/dist/bin/js+0x253616f) (BuildId: 5d053c76aad4cfbd08259f8832e7ac78bbeeab58)
    #3 0x564ac9eac032  (/builds/worker/dist/bin/js+0x31bf032) (BuildId: 5d053c76aad4cfbd08259f8832e7ac78bbeeab58)
    #4 0x0dec477ca22e  (<unknown module>)
```

Without this change, the following symbolization is output:

```
    #0 0x55a6d72f980f in MOZ_CrashSequence /builds/worker/workspace/obj-build/dist/include/mozilla/Assertions.h:248:3
    #1 0x55a6d72f980f in Crash(JSContext*, unsigned int, JS::Value*) /builds/worker/checkouts/gecko/js/src/shell/js.cpp:4223:5
    #2 0x55a6d7421a64 in CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) /builds/worker/checkouts/gecko/js/src/vm/Interpreter.cpp:501:13
    #3 0x55a6d742116f in js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) /builds/worker/checkouts/gecko/js/src/vm/Interpreter.cpp:597:12
    #4 0x55a6d80aa032 in js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICFallbackStub*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) /builds/worker/checkouts/gecko/js/src/jit/BaselineIC.cpp:1705:10
    #4 0x2c803bd8f22e  (<unknown module>)
```

The last frame has a duplicate number. With this change the numbering is
correct:

```
    #0 0x5620c58ec80f in MOZ_CrashSequence /builds/worker/workspace/obj-build/dist/include/mozilla/Assertions.h:248:3
    #1 0x5620c58ec80f in Crash(JSContext*, unsigned int, JS::Value*) /builds/worker/checkouts/gecko/js/src/shell/js.cpp:4223:5
    #2 0x5620c5a14a64 in CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) /builds/worker/checkouts/gecko/js/src/vm/Interpreter.cpp:501:13
    #3 0x5620c5a1416f in js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) /builds/worker/checkouts/gecko/js/src/vm/Interpreter.cpp:597:12
    #4 0x5620c669d032 in js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICFallbackStub*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) /builds/worker/checkouts/gecko/js/src/jit/BaselineIC.cpp:1705:10
    #5 0x349f24c7022e  (<unknown module>)
```
MaskRay pushed a commit that referenced this pull request Oct 13, 2025
@melver
[Clang] Fix brittle print-header-json.c test (llvm#162484)
7815df1 
A recent change adding a new sanitizer kind (via Sanitizers.def) was
reverted in c74fa20 ("Revert "[Clang][CodeGen] Introduce the
AllocToken SanitizerKind" (llvm#162413)"). The reason was this ASan report,
when running the test cases in
clang/test/Preprocessor/print-header-json.c:

```
==clang==483265==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7d82b97e8b58 at pc 0x562cd432231f bp 0x7fff3fad0850 sp 0x7fff3fad0848
READ of size 16 at 0x7d82b97e8b58 thread T0
    #0 0x562cd432231e in __copy_non_overlapping_range<const unsigned long *, const unsigned long *> zorg-test/libcxx_install_asan_ubsan/include/c++/v1/string:2144:38
    #1 0x562cd432231e in void std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::__init_with_size[abi:nn220000]<unsigned long const*, unsigned long const*>(unsigned long const*, unsigned long const*, unsigned long) zorg-test/libcxx_install_asan_ubsan/include/c++/v1/string:2685:18
    #2 0x562cd41e2797 in __init<const unsigned long *, 0> zorg-test/libcxx_install_asan_ubsan/include/c++/v1/string:2673:3
    #3 0x562cd41e2797 in basic_string<const unsigned long *, 0> zorg-test/libcxx_install_asan_ubsan/include/c++/v1/string:1174:5
    #4 0x562cd41e2797 in clang::ASTReader::ReadString(llvm::SmallVectorImpl<unsigned long> const&, unsigned int&) clang/lib/Serialization/ASTReader.cpp:10171:15
    #5 0x562cd41fd89a in clang::ASTReader::ParseLanguageOptions(llvm::SmallVector<unsigned long, 64u> const&, llvm::StringRef, bool, clang::ASTReaderListener&, bool) clang/lib/Serialization/ASTReader.cpp:6475:28
    llvm#6 0x562cd41eea53 in clang::ASTReader::ReadOptionsBlock(llvm::BitstreamCursor&, llvm::StringRef, unsigned int, bool, clang::ASTReaderListener&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&) clang/lib/Serialization/ASTReader.cpp:3069:11
    llvm#7 0x562cd4204ab8 in clang::ASTReader::ReadControlBlock(clang::serialization::ModuleFile&, llvm::SmallVectorImpl<clang::ASTReader::ImportedModule>&, clang::serialization::ModuleFile const*, unsigned int) clang/lib/Serialization/ASTReader.cpp:3249:15
    llvm#8 0x562cd42097d2 in clang::ASTReader::ReadASTCore(llvm::StringRef, clang::serialization::ModuleKind, clang::SourceLocation, clang::serialization::ModuleFile*, llvm::SmallVectorImpl<clang::ASTReader::ImportedModule>&, long, long, clang::ASTFileSignature, unsigned int) clang/lib/Serialization/ASTReader.cpp:5182:15
    llvm#9 0x562cd421ec77 in clang::ASTReader::ReadAST(llvm::StringRef, clang::serialization::ModuleKind, clang::SourceLocation, unsigned int, clang::serialization::ModuleFile**) clang/lib/Serialization/ASTReader.cpp:4828:11
    llvm#10 0x562cd3d07b74 in clang::CompilerInstance::findOrCompileModuleAndReadAST(llvm::StringRef, clang::SourceLocation, clang::SourceLocation, bool) clang/lib/Frontend/CompilerInstance.cpp:1805:27
    llvm#11 0x562cd3d0b2ef in clang::CompilerInstance::loadModule(clang::SourceLocation, llvm::ArrayRef<clang::IdentifierLoc>, clang::Module::NameVisibilityKind, bool) clang/lib/Frontend/CompilerInstance.cpp:1956:31
    llvm#12 0x562cdb04eb1c in clang::Preprocessor::HandleHeaderIncludeOrImport(clang::SourceLocation, clang::Token&, clang::Token&, clang::SourceLocation, clang::detail::SearchDirIteratorImpl<true>, clang::FileEntry const*) clang/lib/Lex/PPDirectives.cpp:2423:49
    llvm#13 0x562cdb042222 in clang::Preprocessor::HandleIncludeDirective(clang::SourceLocation, clang::Token&, clang::detail::SearchDirIteratorImpl<true>, clang::FileEntry const*) clang/lib/Lex/PPDirectives.cpp:2101:17
    llvm#14 0x562cdb043366 in clang::Preprocessor::HandleDirective(clang::Token&) clang/lib/Lex/PPDirectives.cpp:1338:14
    llvm#15 0x562cdafa84bc in clang::Lexer::LexTokenInternal(clang::Token&, bool) clang/lib/Lex/Lexer.cpp:4512:7
    llvm#16 0x562cdaf9f20b in clang::Lexer::Lex(clang::Token&) clang/lib/Lex/Lexer.cpp:3729:24
    llvm#17 0x562cdb0d4ffa in clang::Preprocessor::Lex(clang::Token&) clang/lib/Lex/Preprocessor.cpp:896:11
    llvm#18 0x562cd77da950 in clang::ParseAST(clang::Sema&, bool, bool) clang/lib/Parse/ParseAST.cpp:163:7
    [...]

0x7d82b97e8b58 is located 0 bytes after 3288-byte region [0x7d82b97e7e80,0x7d82b97e8b58)
allocated by thread T0 here:
    #0 0x562cca76f604 in malloc zorg-test/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:67:3
    #1 0x562cd1cce452 in safe_malloc llvm/include/llvm/Support/MemAlloc.h:26:18
    #2 0x562cd1cce452 in llvm::SmallVectorBase<unsigned int>::grow_pod(void*, unsigned long, unsigned long) llvm/lib/Support/SmallVector.cpp:151:15
    #3 0x562cdbe1768b in grow_pod llvm/include/llvm/ADT/SmallVector.h:139:11
    #4 0x562cdbe1768b in grow llvm/include/llvm/ADT/SmallVector.h:525:41
    #5 0x562cdbe1768b in reserve llvm/include/llvm/ADT/SmallVector.h:665:13
    llvm#6 0x562cdbe1768b in llvm::BitstreamCursor::readRecord(unsigned int, llvm::SmallVectorImpl<unsigned long>&, llvm::StringRef*) llvm/lib/Bitstream/Reader/BitstreamReader.cpp:230:10
    llvm#7 0x562cd41ee8ab in clang::ASTReader::ReadOptionsBlock(llvm::BitstreamCursor&, llvm::StringRef, unsigned int, bool, clang::ASTReaderListener&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&) clang/lib/Serialization/ASTReader.cpp:3060:49
    llvm#8 0x562cd4204ab8 in clang::ASTReader::ReadControlBlock(clang::serialization::ModuleFile&, llvm::SmallVectorImpl<clang::ASTReader::ImportedModule>&, clang::serialization::ModuleFile const*, unsigned int) clang/lib/Serialization/ASTReader.cpp:3249:15
    llvm#9 0x562cd42097d2 in clang::ASTReader::ReadASTCore(llvm::StringRef, clang::serialization::ModuleKind, clang::SourceLocation, clang::serialization::ModuleFile*, llvm::SmallVectorImpl<clang::ASTReader::ImportedModule>&, long, long, clang::ASTFileSignature, unsigned int) clang/lib/Serialization/ASTReader.cpp:5182:15
    llvm#10 0x562cd421ec77 in clang::ASTReader::ReadAST(llvm::StringRef, clang::serialization::ModuleKind, clang::SourceLocation, unsigned int, clang::serialization::ModuleFile**) clang/lib/Serialization/ASTReader.cpp:4828:11
    llvm#11 0x562cd3d07b74 in clang::CompilerInstance::findOrCompileModuleAndReadAST(llvm::StringRef, clang::SourceLocation, clang::SourceLocation, bool) clang/lib/Frontend/CompilerInstance.cpp:1805:27
    llvm#12 0x562cd3d0b2ef in clang::CompilerInstance::loadModule(clang::SourceLocation, llvm::ArrayRef<clang::IdentifierLoc>, clang::Module::NameVisibilityKind, bool) clang/lib/Frontend/CompilerInstance.cpp:1956:31
    llvm#13 0x562cdb04eb1c in clang::Preprocessor::HandleHeaderIncludeOrImport(clang::SourceLocation, clang::Token&, clang::Token&, clang::SourceLocation, clang::detail::SearchDirIteratorImpl<true>, clang::FileEntry const*) clang/lib/Lex/PPDirectives.cpp:2423:49
    llvm#14 0x562cdb042222 in clang::Preprocessor::HandleIncludeDirective(clang::SourceLocation, clang::Token&, clang::detail::SearchDirIteratorImpl<true>, clang::FileEntry const*) clang/lib/Lex/PPDirectives.cpp:2101:17
    llvm#15 0x562cdb043366 in clang::Preprocessor::HandleDirective(clang::Token&) clang/lib/Lex/PPDirectives.cpp:1338:14
    llvm#16 0x562cdafa84bc in clang::Lexer::LexTokenInternal(clang::Token&, bool) clang/lib/Lex/Lexer.cpp:4512:7
    llvm#17 0x562cdaf9f20b in clang::Lexer::Lex(clang::Token&) clang/lib/Lex/Lexer.cpp:3729:24
    llvm#18 0x562cdb0d4ffa in clang::Preprocessor::Lex(clang::Token&) clang/lib/Lex/Preprocessor.cpp:896:11
    llvm#19 0x562cd77da950 in clang::ParseAST(clang::Sema&, bool, bool) clang/lib/Parse/ParseAST.cpp:163:7
    [...]

SUMMARY: AddressSanitizer: heap-buffer-overflow clang/lib/Serialization/ASTReader.cpp:10171:15 in clang::ASTReader::ReadString(llvm::SmallVectorImpl<unsigned long> const&, unsigned int&)
```

The reason is this particular RUN line:
```
// RUN: env CC_PRINT_HEADERS_FORMAT=json CC_PRINT_HEADERS_FILTERING=direct-per-file CC_PRINT_HEADERS_FILE=%t.txt %clang -fsyntax-only -I %S/Inputs/print-header-json -isystem %S/Inputs/print-header-json/system -fmodules -fimplicit-module-maps -fmodules-cache-path=%t %s -o /dev/null
```

which was added in 8df194f ("[Clang] Support includes translated to
module imports in -header-include-filtering=direct-per-file (llvm#156756)").

The problem is caused by an incremental build reusing stale cached
module files (.pcm) that are no longer binary-compatible with the
updated compiler. Adding a new sanitizer option altered the implicit
binary layout of the serialized LangOptions data structure. The build +
test system is oblivious to such changes. When the new compiler
attempted to read the old module file (from the previous test
invocation), it misinterpreted the data due to the layout mismatch,
resulting in a heap-buffer-overflow. Unfortunately Clang's PCM format
does not encode nor detect version mismatches here; a more graceful
failure mode would be preferable.

For now, fix the test to be more robust with incremental build + test.
MaskRay pushed a commit that referenced this pull request Oct 26, 2025
@davidmrdavid @antoniofrighetto
[ASan] Do not instrument catch block parameters on Windows (llvm#159618)
90e0933 
**Mitigation for:** google/sanitizers#749

**Disclosure:** I'm not an ASan compiler expert yet (I'm trying to
learn!), I primarily work in the runtime. Some of this PR was developed
with the help of AI tools (primarily as a "fuzzy `grep` engine"), but
I've manually refined and tested the output, and can speak for every
line. In general, I used it only to orient myself and for
"rubberducking".

**Context:**

The msvc ASan team (👋 ) has received an internal request to improve
clang's exception handling under ASan for Windows. Namely, we're
interested in **mitigating** this bug:
google/sanitizers#749

To summarize, today, clang + ASan produces a false-positive error for
this program:

```C++
#include <cstdio>
#include <exception>
int main()
{
	try	{
		throw std::exception("test");
	}catch (const std::exception& ex){
		puts(ex.what());
	}
	return 0;
}
```

The error reads as such:


```
C:\Users\dajusto\source\repros\upstream>type main.cpp
#include <cstdio>
#include <exception>
int main()
{
        try     {
                throw std::exception("test");
        }catch (const std::exception& ex){
                puts(ex.what());
        }
        return 0;
}
C:\Users\dajusto\source\repros\upstream>"C:\Users\dajusto\source\repos\llvm-project\build.runtimes\bin\clang.exe" -fsanitize=address -g -O0 main.cpp

C:\Users\dajusto\source\repros\upstream>a.exe
=================================================================
==19112==ERROR: AddressSanitizer: access-violation on unknown address 0x000000000000 (pc 0x7ff72c7c11d9 bp 0x0080000ff960 sp 0x0080000fcf50 T0)
==19112==The signal is caused by a READ memory access.
==19112==Hint: address points to the zero page.
    #0 0x7ff72c7c11d8 in main C:\Users\dajusto\source\repros\upstream\main.cpp:8
    #1 0x7ff72c7d479f in _CallSettingFrame C:\repos\msvc\src\vctools\crt\vcruntime\src\eh\amd64\handlers.asm:49
    #2 0x7ff72c7c8944 in __FrameHandler3::CxxCallCatchBlock(struct _EXCEPTION_RECORD *) C:\repos\msvc\src\vctools\crt\vcruntime\src\eh\frame.cpp:1567
    #3 0x7ffb4a90e3e5  (C:\WINDOWS\SYSTEM32\ntdll.dll+0x18012e3e5)
    #4 0x7ff72c7c1128 in main C:\Users\dajusto\source\repros\upstream\main.cpp:6
    #5 0x7ff72c7c33db in invoke_main C:\repos\msvc\src\vctools\crt\vcstartup\src\startup\exe_common.inl:78
    llvm#6 0x7ff72c7c33db in __scrt_common_main_seh C:\repos\msvc\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
    llvm#7 0x7ffb49b05c06  (C:\WINDOWS\System32\KERNEL32.DLL+0x180035c06)
    llvm#8 0x7ffb4a8455ef  (C:\WINDOWS\SYSTEM32\ntdll.dll+0x1800655ef)

==19112==Register values:
rax = 0  rbx = 80000ff8e0  rcx = 27d76d00000  rdx = 80000ff8e0
rdi = 80000fdd50  rsi = 80000ff6a0  rbp = 80000ff960  rsp = 80000fcf50
r8  = 100  r9  = 19930520  r10 = 8000503a90  r11 = 80000fd540
r12 = 80000fd020  r13 = 0  r14 = 80000fdeb8  r15 = 0
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: access-violation C:\Users\dajusto\source\repros\upstream\main.cpp:8 in main
==19112==ABORTING
```

The root of the issue _appears to be_ that ASan's instrumentation is
incompatible with Window's assumptions for instantiating `catch`-block's
parameters (`ex` in the snippet above).

The nitty gritty details are lost on me, but I understand that to make
this work without loss of ASan coverage, a "serious" refactoring is
needed. In the meantime, users risk false positive errors when pairing
ASan + catch-block parameters on Windows.

**To mitigate this** I think we should avoid instrumenting catch-block
parameters on Windows. It appears to me this is as "simple" as marking
catch block parameters as "uninteresting" in
`AddressSanitizer::isInterestingAlloca`. My manual tests seem to confirm
this.

I believe this is strictly better than today's status quo, where the
runtime generates false positives. Although we're now explicitly
choosing to instrument less, the benefit is that now more programs can
run with ASan without _funky_ macros that disable ASan on exception
blocks.

**This PR:** implements the mitigation above, and creates a simple new
test for it.

_Thanks!_

---------

Co-authored-by: Antonio Frighetto <me@antoniofrighetto.com>
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2 participants

@MaskRay