[LLDB][MIPS] Fix signal SIGBUS number mismatch error on mips target #132688

yingopq · 2025-03-24T07:53:41Z

Now, because we do not support mips debugging, if we compile LLVM on mips target, would report error static assertion failed:Value mismatch for signal number SIGBUS, so add this condition to avoid error.

llvmbot · 2025-03-24T07:54:16Z

@llvm/pr-subscribers-lldb

Author: None (yingopq)

Changes

MIPS changed the SIGBUS signal number to be the same as other architectures. So we would fail to compile llvm on mips. The relevant modification link is:
https://reviews.llvm.org/D146285

Full diff: https://github.com/llvm/llvm-project/pull/132688.diff

1 Files Affected:

(modified) lldb/source/Plugins/Process/Utility/LinuxSignals.cpp (+16-5)

diff --git a/lldb/source/Plugins/Process/Utility/LinuxSignals.cpp b/lldb/source/Plugins/Process/Utility/LinuxSignals.cpp
index eaecc84df15d4..aaada3b1e4c8f 100644
--- a/lldb/source/Plugins/Process/Utility/LinuxSignals.cpp
+++ b/lldb/source/Plugins/Process/Utility/LinuxSignals.cpp
@@ -61,10 +61,17 @@ void LinuxSignals::Reset() {
   AddSignal(5,      "SIGTRAP",      true,     true,   true,   "trace trap (not reset when caught)");
   AddSignal(6,      "SIGABRT",      false,    true,   true,   "abort()/IOT trap", "SIGIOT");
 
-  AddSignal(7,      "SIGBUS",       false,    true,   true,   "bus error");
-  ADD_SIGCODE(SIGBUS, 7, BUS_ADRALN, 1, "illegal alignment");
-  ADD_SIGCODE(SIGBUS, 7, BUS_ADRERR, 2, "illegal address");
-  ADD_SIGCODE(SIGBUS, 7, BUS_OBJERR, 3, "hardware error");
+#if defined(mips) || defined(__mips__) || defined(__mips)
+    AddSignal(10,      "SIGBUS",       false,    true,   true,   "bus error");
+    ADD_SIGCODE(SIGBUS, 10, BUS_ADRALN, 1, "illegal alignment");
+    ADD_SIGCODE(SIGBUS, 10, BUS_ADRERR, 2, "illegal address");
+    ADD_SIGCODE(SIGBUS, 10, BUS_OBJERR, 3, "hardware error");
+#else
+    AddSignal(7,      "SIGBUS",       false,    true,   true,   "bus error");
+    ADD_SIGCODE(SIGBUS, 7, BUS_ADRALN, 1, "illegal alignment");
+    ADD_SIGCODE(SIGBUS, 7, BUS_ADRERR, 2, "illegal address");
+    ADD_SIGCODE(SIGBUS, 7, BUS_OBJERR, 3, "hardware error");
+#endif
 
   AddSignal(8,      "SIGFPE",       false,    true,   true,   "floating point exception");
   ADD_SIGCODE(SIGFPE, 8, FPE_INTDIV, 1, "integer divide by zero");
@@ -77,7 +84,11 @@ void LinuxSignals::Reset() {
   ADD_SIGCODE(SIGFPE, 8, FPE_FLTSUB, 8, "subscript out of range");
 
   AddSignal(9,      "SIGKILL",      false,    true,   true,   "kill");
-  AddSignal(10,     "SIGUSR1",      false,    true,   true,   "user defined signal 1");
+#if defined(mips) || defined(__mips__) || defined(__mips)
+    AddSignal(7,     "SIGUSR1",      false,    true,   true,   "user defined signal 1");
+#else
+    AddSignal(10,     "SIGUSR1",      false,    true,   true,   "user defined signal 1");
+#endif
 
   AddSignal(11,     "SIGSEGV",      false,    true,   true,   "segmentation violation");
   ADD_SIGCODE(SIGSEGV, 11, SEGV_MAPERR,  1, "address not mapped to object", SignalCodePrintOption::Address);

DavidSpickett · 2025-03-25T16:50:36Z

MIPS changed the SIGBUS signal number to be the same as other architectures.

But your change appears to use different numbers for MIPS, which looks like the opposite.

Also please cite in the PR description the changes in the Linux Kernel that did this.

Also I'm pretty sure @labath removed a bunch of Linux MIPS support code at some point due to lack of use. So if you are about to add it all back, it would be good to know what your use case here is. Are you trying to get LLDB on MIPS Linux working again?

(we still support MIPS FreeBSD, though the latest FreeBSD release has dropped it)

DavidSpickett · 2025-03-25T16:55:17Z

lldb/source/Plugins/Process/Utility/LinuxSignals.cpp

+    ADD_SIGCODE(SIGBUS, 7, BUS_ADRALN, 1, "illegal alignment");
+    ADD_SIGCODE(SIGBUS, 7, BUS_ADRERR, 2, "illegal address");
+    ADD_SIGCODE(SIGBUS, 7, BUS_OBJERR, 3, "hardware error");
+#endif


I suspect that this code is also used in the lldb client, which may be built on a platform other than the target platform. For example, I can debug MIPS Linux remotely from a Mac OS host. It will need to be a runtime check in this case, and the compile time checks relaxed.

If this code only ever runs in lldb-server, then it could be fine.

yingopq · 2025-03-26T09:40:37Z

MIPS changed the SIGBUS signal number to be the same as other architectures.

But your change appears to use different numbers for MIPS, which looks like the opposite.

Also please cite in the PR description the changes in the Linux Kernel that did this.

Also I'm pretty sure @labath removed a bunch of Linux MIPS support code at some point due to lack of use. So if you are about to add it all back, it would be good to know what your use case here is. Are you trying to get LLDB on MIPS Linux working again?

(we still support MIPS FreeBSD, though the latest FreeBSD release has dropped it)

There has a issue, when we compile LLVM of rust on mips, target we will face an error static assertion failed:Value mismatch for signal number SIGBUS, and after we revert https://reviews.llvm.org/D146285, can compile success; But this error did not occur on x86 target.
Check the file /usr/include/mipsel-linux-gnu/asm/signal.hon mips, the number is 10;
Check the file /usr/mips-linux-gnu/include/asm/signal.h on x86, the number is 7.

And now I did not has a clear test case, just found this problem when compiling.
So did we need to add check before ADD_SIGCODE(SIGBUS, 7, BUS_ADRALN, 1, "illegal alignment"); ?

labath · 2025-03-26T09:56:41Z

This needs to be a runtime instead of a build-time choice, because we support debugging foreign architectures, so I guess that what you need is more closer to reverting 93a4553.

However, your last comment makes me suspect you don't actually care about lldb+mips working, and just want to get rust building. Is that the case? If it is, then we may just want to make this build in that configuration, but not actually claim to support mips debugging (in theory, you should still be able to debug e.g. x86 core files with a mips build of lldb)

labath · 2025-03-26T10:00:41Z

If it is, then we may just want to make this build in that configuration, but not actually claim to support mips debugging (in theory, you should still be able to debug e.g. x86 core files with a mips build of lldb)

One way to do that would be to change #ifdef __linux__ on line 11 to #if defined(__linux__) && !defined(__mips__) and add a comment to say that this is because we don't support mips debugging.

github-actions · 2025-03-31T02:38:49Z

✅ With the latest revision this PR passed the C/C++ code formatter.

labath

LGTM, I just tweaked the comment a bit. Please also update the endif comment on line 39.

labath · 2025-03-31T11:01:41Z

lldb/source/Plugins/Process/Utility/LinuxSignals.cpp

+// Now, because we do not support mips debugging, if we compile LLVM on mips
+// target, would report error `static assertion failed:Value mismatch for signal
+// number SIGBUS`, so add this condition to avoid error.


Suggested change

// Now, because we do not support mips debugging, if we compile LLVM on mips

// target, would report error `static assertion failed:Value mismatch for signal

// number SIGBUS`, so add this condition to avoid error.

// mips-linux debugging is not supported and mips uses different numbers for some signals (e.g. SIGBUS) on linux, so we skip the static checks below. The definitions here can be used for debugging non-mips targets on a mips-hosted lldb.

OK, thanks!

@labath please help review again, thanks!

Now, because we do not support mips debugging, if we compile LLVM on mips target, would report error `static assertion failed:Value mismatch for signal number SIGBUS`, so add this condition to avoid error.

labath · 2025-04-09T08:53:37Z

The patch (still) looks good. I think what you need is for someone to push the submit button, so I'll do that now.

…lvm#132688) Now, because we do not support mips debugging, if we compile LLVM on mips target, would report error `static assertion failed:Value mismatch for signal number SIGBUS`, so add this condition to avoid error.

yingopq requested a review from JDevlieghere as a code owner March 24, 2025 07:53

llvmbot added the lldb label Mar 24, 2025

yingopq removed the request for review from JDevlieghere March 24, 2025 08:38

DavidSpickett changed the title ~~[Mips] Fix signal number of SIGBUS on mips~~ [LLDB][MIPS] Fix signal number of SIGBUS on mips Mar 25, 2025

DavidSpickett reviewed Mar 25, 2025

View reviewed changes

yingopq force-pushed the Fix_bug_issue_3 branch from e8cf384 to 1b1285a Compare March 31, 2025 02:36

yingopq changed the title ~~[LLDB][MIPS] Fix signal number of SIGBUS on mips~~ [LLDB][MIPS] Fix signal SIGBUS number mismatch error on mips target Mar 31, 2025

yingopq force-pushed the Fix_bug_issue_3 branch from 1b1285a to 6b95040 Compare March 31, 2025 02:38

labath approved these changes Mar 31, 2025

View reviewed changes

yingopq force-pushed the Fix_bug_issue_3 branch from 6b95040 to 4cd95bb Compare April 1, 2025 06:54

[LLDB][MIPS] Fix signal SIGBUS number mismatch error on mips target

61901c7

Now, because we do not support mips debugging, if we compile LLVM on mips target, would report error `static assertion failed:Value mismatch for signal number SIGBUS`, so add this condition to avoid error.

yingopq force-pushed the Fix_bug_issue_3 branch from 4cd95bb to 61901c7 Compare April 1, 2025 06:57

labath merged commit 8877b91 into llvm:main Apr 9, 2025
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[LLDB][MIPS] Fix signal SIGBUS number mismatch error on mips target #132688

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