ELF: Synthesize R_RISCV_ALIGN at input section start #5
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
MaskRay
force-pushed
the
lld-riscv-align
branch
4 times, most recently
from
01cc246 to
4298172
Compare
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
force-pushed
the
lld-riscv-align
branch
from
4298172 to
fabd55d
Compare
|
This is a draft o llvm#151639 , which has been merged |
MaskRay
pushed a commit
that referenced
this pull request
Aug 15, 2025
## 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
…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.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
See also https://sourceware.org/bugzilla/show_bug.cgi?id=33236