Backport b31bbfcf2f13fa5b16762f5384d95c2b5d9c5705

Author: TheRealMDoerr

src/hotspot/share/code/codeBlob.cpp

@@ -672,6 +672,7 @@ void CodeBlob::dump_for_addr(address addr, outputStream* st, bool verbose) const
       nm->print_nmethod(true);
     } else {
       nm->print(st);
+      nm->print_code_snippet(st, addr);
     }
     return;
   }

src/hotspot/share/code/nmethod.cpp

@@ -3385,6 +3385,46 @@ void nmethod::print_value_on(outputStream* st) const {
 }
 #endif
 
+void nmethod::print_code_snippet(outputStream* st, address addr) const {
+  if (entry_point() <= addr && addr < code_end()) {
+    // Pointing into the nmethod's code. Try to disassemble some instructions around addr.
+    // Determine conservative start and end points.
+    address start;
+    if (frame_complete_offset() != CodeOffsets::frame_never_safe &&
+        addr >= code_begin() + frame_complete_offset()) {
+      start = code_begin() + frame_complete_offset();
+    } else {
+      start = (addr < verified_entry_point()) ? entry_point() : verified_entry_point();
+    }
+    address start_for_hex_dump = start; // We can choose a different starting point for hex dump, below.
+    address end = code_end();
+
+    // Try using relocations to find closer instruction start and end points.
+    // (Some platforms have variable length instructions and can only
+    // disassemble correctly at instruction start addresses.)
+    RelocIterator iter((nmethod*)this, start);
+    while (iter.next() && iter.addr() < addr) { // find relocation before addr
+      // Note: There's a relocation which doesn't point to an instruction start:
+      // ZBarrierRelocationFormatStoreGoodAfterMov with ZGC on x86_64
+      // We could detect and skip it, but hex dump is still usable when
+      // disassembler produces garbage in such a very rare case.
+      start = iter.addr();
+      // We want at least 64 Bytes ahead in hex dump.
+      if (iter.addr() <= (addr - 64)) start_for_hex_dump = iter.addr();
+    }
+    if (iter.has_current()) {
+      if (iter.addr() == addr) iter.next(); // find relocation after addr
+      if (iter.has_current()) end = iter.addr();
+    }
+
+    // Always print hex. Disassembler may still have problems when hitting an incorrect instruction start.
+    os::print_hex_dump(st, start_for_hex_dump, end, 1, /* print_ascii=*/false);
+    if (!Disassembler::is_abstract()) {
+      Disassembler::decode(start, end, st);
+    }
+  }
+}
+
 #ifndef PRODUCT
 
 void nmethod::print_calls(outputStream* st) {

src/hotspot/share/code/nmethod.hpp

@@ -623,6 +623,7 @@ class nmethod : public CompiledMethod {
   void print()                          const;
   void print(outputStream* st)          const;
   void print_code();
+  void print_code_snippet(outputStream* st, address addr) const;
 
 #if defined(SUPPORT_DATA_STRUCTS)
   // print output in opt build for disassembler library