Core: Register @bpfglobal variables in a symbol table

globals_processing emitted each global and forgot it, which is why nothing
could ever read one back. Each integer-scalar global now lands in
CompilationContext.bpf_globals as a BpfGlobalSymbol; non-scalar globals get a
clear NotImplementedError instead of emitting something unusable. LICENSE stays
special-cased and unaffected.

Alignment becomes natural (width/8) instead of a blanket 8, matching what clang
emits for the same declarations in tests/c-form/global_vars.bpf.c -- llc
derives the BTF DATASEC layout from these symbols.

Also adds current_func_globals to the context for the upcoming write support.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L1PX8EuP9C3o3veWGA84RF

Author: r41k0u

pythonbpf/context.py

@@ -5,6 +5,7 @@
 if TYPE_CHECKING:
     from pythonbpf.structs.struct_type import StructType
     from pythonbpf.maps.maps_utils import MapSymbol
+    from pythonbpf.globals_pass import BpfGlobalSymbol
 
 logger = logging.getLogger(__name__)
 
@@ -66,6 +67,11 @@ def __init__(self, module: ir.Module):
         self.global_sym_tab: list[ir.GlobalVariable] = []
         self.structs_sym_tab: dict[str, "StructType"] = {}
         self.map_sym_tab: dict[str, "MapSymbol"] = {}
+        self.bpf_globals: dict[str, "BpfGlobalSymbol"] = {}
+
+        # Names a `global` statement declared writable in the function whose
+        # body is currently being emitted; managed by process_func_body.
+        self.current_func_globals: set[str] = set()
 
         # Helper management
         self.scratch_pool = ScratchPoolManager()
@@ -80,3 +86,4 @@ def reset(self):
         """Reset state between functions if necessary, though new context per compile is preferred."""
         self.scratch_pool.reset()
         self.current_func = None
+        self.current_func_globals = set()

pythonbpf/globals_pass.py

@@ -1,13 +1,28 @@
 from llvmlite import ir
 import ast
 
+from dataclasses import dataclass
 from logging import Logger
 import logging
 from .type_deducer import ctypes_to_ir
 
 logger: Logger = logging.getLogger(__name__)
 
 
+@dataclass
+class BpfGlobalSymbol:
+    """A mutable BPF global variable declared with @bpfglobal.
+
+    Lands in .bss (zero initializer) or .data (non-zero) and is read with a
+    plain load / written with a plain store; libbpf exposes the sections to
+    userspace as global-data maps.
+    """
+
+    var: ir.GlobalVariable
+    ir_type: ir.Type
+    ctype_name: str
+
+
 def populate_global_symbol_table(tree, compilation_context):
     """
     compilation_context: CompilationContext
@@ -68,7 +83,11 @@ def _emit_global(module: ir.Module, node, name):
 
     gvar = ir.GlobalVariable(module, ty, name=name)
     gvar.initializer = llvm_init
-    gvar.align = 8
+    # Natural alignment, matching what clang emits for the same declaration
+    # (align 4 for i32, align 8 for i64). llc derives the BTF DATASEC layout
+    # from these symbols, so the alignment should mirror the C reference in
+    # tests/c-form/global_vars.bpf.c.
+    gvar.align = ty.width // 8 if isinstance(ty, ir.IntType) else 8
     gvar.linkage = "dso_local"
     gvar.global_constant = False
     return gvar
@@ -111,7 +130,19 @@ def globals_processing(tree, compilation_context):
                         node.body[0].value, (ast.Constant, ast.Name, ast.Call)
                     )
                 ):
-                    _emit_global(compilation_context.module, node, name)
+                    gvar = _emit_global(compilation_context.module, node, name)
+                    if isinstance(gvar.value_type, ir.IntType):
+                        compilation_context.bpf_globals[name] = BpfGlobalSymbol(
+                            var=gvar,
+                            ir_type=gvar.value_type,
+                            ctype_name=node.returns.id,
+                        )
+                    else:
+                        raise NotImplementedError(
+                            f"Global '{name}': only integer scalar globals are "
+                            f"supported so far; '{node.returns.id}' globals are "
+                            f"planned for a later milestone"
+                        )
                 else:
                     raise SyntaxError(f"ERROR: Invalid syntax for {name} global")