Fix unaligned map key access

If we have a map with key type [string[9], int64], then the int64 should
be treated as an unaligned access.

Previously the alignment calculations worked off the length of the
string value, not the maximum size allocated for the string key.

Example:
  @mapa["ccccdddd", 0] = 1;
  @mapa["aaaabbb", 0] = 1;

The string key's size is taken from the maximum string length, which is
9 bytes. Fields after this key should be considered unaligned.

The second line contains a string of 8 bytes. Padding was not taken
into account and the following key(s) were incorrectly treated as
aligned.

CHANGELOG.md

@@ -33,6 +33,8 @@ and this project adheres to
 #### Fixed
 - Fix segfault for multi-tracepoint probes
   - [#3274](https://github.com/bpftrace/bpftrace/pull/3274)
+- Fix verifier error from misaligned stack access when using strings as map keys
+  - [#3294](https://github.com/bpftrace/bpftrace/issues/3294)
 #### Security
 #### Docs
 - Remove mention of unsupported character literals

src/ast/passes/codegen_llvm.cpp

@@ -2844,13 +2844,13 @@ AllocaInst *CodegenLLVM::getMultiMapKey(Map &map,
       if (expr->type.IsStringTy() && expr->type.GetSize() < map_key_size)
         b_.CreateMemsetBPF(offset_val, b_.getInt8(0), map_key_size);
       b_.CREATE_MEMCPY(offset_val, expr_, expr->type.GetSize(), 1);
-      if ((expr->type.GetSize() % 8) != 0)
+      if ((map_key_size % 8) != 0)
         aligned = false;
     } else {
       if (expr->type.IsArrayTy() || expr->type.IsRecordTy()) {
         // Read the array/struct into the key
         b_.CreateProbeRead(ctx_, offset_val, expr->type, expr_, expr->loc);
-        if ((expr->type.GetSize() % 8) != 0)
+        if ((map_key_size % 8) != 0)
           aligned = false;
       } else {
         // promote map key to 64-bit:

tests/runtime/regression

@@ -97,3 +97,8 @@ PROG kfunc:__module_get { print(args.module->trace_events[1]->flags); exit(); }
 AFTER lsmod
 EXPECT Attaching 1 probe...
 TIMEOUT 1
+
+NAME unaligned key with aligned value
+PROG BEGIN { @mapA["aaaabbb", 0] = 1; @mapA["ccccdddd", 0] = 1; }
+EXPECT Attaching 1 probe...
+TIMEOUT 1