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feat: Generate calls via the GOT
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This change involves moving the generation of the GOT from
variable_generator.rs to codegen.rs, in order to also cover not only
global variables but also functions and 'programs' too. Once these have
been given an associated index in the GOT we can use that to replace
normal direct function calls with indirect calls to a function pointer
stored in the GOT. We don't do this for calls with external linkage
since these won't be subject to online change.
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@lewis-revill
lewis-revill committed Jun 19, 2024
1 parent 3a0e1a5 commit e80995a
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Showing 3 changed files with 152 additions and 89 deletions.
104 changes: 103 additions & 1 deletion src/codegen.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
// Copyright (c) 2020 Ghaith Hachem and Mathias Rieder
use std::{
cell::RefCell,
collections::HashMap,
fs,
ops::Deref,
path::{Path, PathBuf},
};
Expand Down Expand Up @@ -34,6 +36,7 @@ use inkwell::{
module::Module,
passes::PassBuilderOptions,
targets::{CodeModel, FileType, InitializationConfig, RelocMode},
types::BasicTypeEnum,
};
use plc_ast::ast::{CompilationUnit, LinkageType};
use plc_diagnostics::diagnostics::Diagnostic;
Expand Down Expand Up @@ -84,6 +87,40 @@ pub struct GeneratedModule<'ink> {
type MainFunction<T, U> = unsafe extern "C" fn(*mut T) -> U;
type MainEmptyFunction<U> = unsafe extern "C" fn() -> U;

pub fn read_got_layout(location: &str, format: ConfigFormat) -> Result<HashMap<String, u64>, Diagnostic> {
if !Path::new(location).is_file() {
// Assume if the file doesn't exist that there is no existing GOT layout yet. write_got_layout will handle
// creating our file when we want to.
return Ok(HashMap::new());
}

let s =
fs::read_to_string(location).map_err(|_| Diagnostic::new("GOT layout could not be read from file"))?;
match format {
ConfigFormat::JSON => serde_json::from_str(&s)
.map_err(|_| Diagnostic::new("Could not deserialize GOT layout from JSON")),
ConfigFormat::TOML => {
toml::de::from_str(&s).map_err(|_| Diagnostic::new("Could not deserialize GOT layout from TOML"))
}
}
}

pub fn write_got_layout(
got_entries: HashMap<String, u64>,
location: &str,
format: ConfigFormat,
) -> Result<(), Diagnostic> {
let s = match format {
ConfigFormat::JSON => serde_json::to_string(&got_entries)
.map_err(|_| Diagnostic::new("Could not serialize GOT layout to JSON"))?,
ConfigFormat::TOML => toml::ser::to_string(&got_entries)
.map_err(|_| Diagnostic::new("Could not serialize GOT layout to TOML"))?,
};

fs::write(location, s).map_err(|_| Diagnostic::new("GOT layout could not be written to file"))?;
Ok(())
}

impl<'ink> CodeGen<'ink> {
/// constructs a new code-generator that generates CompilationUnits into a module with the given module_name
pub fn new(
Expand Down Expand Up @@ -127,14 +164,79 @@ impl<'ink> CodeGen<'ink> {
annotations,
&index,
&mut self.debug,
self.got_layout_file.clone(),
);

//Generate global variables
let llvm_gv_index =
variable_generator.generate_global_variables(dependencies, &self.module_location)?;
index.merge(llvm_gv_index);

// Build our GOT layout here. We need to find all the names for globals, programs, and
// functions and assign them indices in the GOT, taking into account prior indices.
let program_globals = global_index
.get_program_instances()
.into_iter()
.fold(Vec::new(), |mut acc, p| {
acc.push(p.get_name());
acc.push(p.get_qualified_name());
acc
});
let functions = global_index.get_pous().values()
.filter_map(|p| match p {
PouIndexEntry::Function { name, linkage: LinkageType::Internal, is_generated: false, .. }
| PouIndexEntry::FunctionBlock { name, linkage: LinkageType::Internal, .. } => Some(name.as_ref()),
_ => None,
});
let all_names = global_index
.get_globals()
.values()
.map(|g| g.get_qualified_name())
.chain(program_globals)
.chain(functions)
.map(|n| n.to_lowercase());

if let Some((location, format)) = &self.got_layout_file {
let got_entries = read_got_layout(location.as_str(), *format)?;
let mut new_symbols = Vec::new();
let mut new_got_entries = HashMap::new();
let mut new_got = HashMap::new();

for name in all_names {
if let Some(idx) = got_entries.get(&name.to_string()) {
new_got_entries.insert(name.to_string(), *idx);
index.associate_got_index(&name, *idx)?;
new_got.insert(*idx, name.to_string());
} else {
new_symbols.push(name.to_string());
}
}

// Put any names that weren't there last time in any free space in the GOT.
let mut idx: u64 = 0;
for name in &new_symbols {
while new_got.contains_key(&idx) {
idx += 1;
}
new_got_entries.insert(name.to_string(), idx);
index.associate_got_index(name, idx)?;
new_got.insert(idx, name.to_string());
}

// Now we can write new_got_entries back out to a file.
write_got_layout(new_got_entries, location.as_str(), *format)?;

// Construct our GOT as a new global array. We initialise this array in the loader code.
let got_size = new_got.keys().max().map_or(0, |m| *m + 1);
let _got = llvm.create_global_variable(
&self.module,
"__custom_got",
BasicTypeEnum::ArrayType(Llvm::get_array_type(
BasicTypeEnum::PointerType(llvm.context.i8_type().ptr_type(0.into())),
got_size.try_into().expect("the computed custom GOT size is too large"),
)),
);
}

//Generate opaque functions for implementations and associate them with their types
let llvm = Llvm::new(context, context.create_builder());
let llvm_impl_index = pou_generator::generate_implementation_stubs(
Expand Down
51 changes: 47 additions & 4 deletions src/codegen/generators/expression_generator.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,10 +17,10 @@ use crate::{
};
use inkwell::{
builder::Builder,
types::{BasicType, BasicTypeEnum},
types::{BasicType, BasicTypeEnum, FunctionType},
values::{
ArrayValue, BasicMetadataValueEnum, BasicValue, BasicValueEnum, FloatValue, IntValue, PointerValue,
StructValue, VectorValue,
ArrayValue, BasicMetadataValueEnum, BasicValue, BasicValueEnum, CallableValue,
CallSiteValue, FloatValue, IntValue, PointerValue, StructValue, VectorValue,
},
AddressSpace, FloatPredicate, IntPredicate,
};
Expand Down Expand Up @@ -318,6 +318,41 @@ impl<'ink, 'b> ExpressionCodeGenerator<'ink, 'b> {
}
}

/// Generate an access to the appropriate GOT entry to achieve a call to the given function.
pub fn generate_got_call(
&self,
qualified_name: &str,
function_type: &FunctionType<'ink>,
args: &[BasicMetadataValueEnum<'ink>],
) -> Result<Option<CallSiteValue<'ink>>, Diagnostic> {
// We will generate a GEP, which has as its base address the magic constant which
// will eventually be replaced by the location of the GOT.
let base = self
.llvm
.context
.i64_type()
.const_int(0xdeadbeef00000000, false)
.const_to_pointer(llvm_type
.ptr_type(AddressSpace::default())
.ptr_type(AddressSpace::default()));

self.llvm_index
.find_got_index(qualified_name)
.map(|idx| {
let mut ptr = self.llvm.load_array_element(
base,
&[self.llvm.context.i32_type().const_int(idx, false)],
"",
)?;
ptr = self.llvm.load_pointer(&ptr, "").into_pointer_value();
let callable = CallableValue::try_from(ptr)
.map_err(|_| Diagnostic::new("Pointer was not a function pointer"))?;

Ok(self.llvm.builder.build_call(callable, args, "call"))
})
.transpose()
}

/// generates a binary expression (e.g. a + b, x AND y, etc.) and returns the resulting `BasicValueEnum`
/// - `left` the AstStatement left of the operator
/// - `right` the AstStatement right of the operator
Expand Down Expand Up @@ -514,9 +549,17 @@ impl<'ink, 'b> ExpressionCodeGenerator<'ink, 'b> {
None
};

// Check for the function within the GOT. If it's there, we need to generate an indirect
// call to its location within the GOT, which should contain a function pointer.
// First get the function type so our function pointer can have the correct type.
let qualified_name = self.annotations.get_qualified_name(operator)
.expect("Shouldn't have got this far without a name for the function");
let function_type = function.get_type();
let call = self.generate_got_call(qualified_name, &function_type, &arguments_list)?
.unwrap_or_else(|| self.llvm.builder.build_call(function, &arguments_list, "call"));

// if the target is a function, declare the struct locally
// assign all parameters into the struct values
let call = &self.llvm.builder.build_call(function, &arguments_list, "call");

// so grab either:
// - the out-pointer if we generated one in by_ref_func_out
Expand Down
86 changes: 2 additions & 84 deletions src/codegen/generators/variable_generator.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,11 @@ use crate::{
codegen::{debug::Debug, llvm_index::LlvmTypedIndex, llvm_typesystem::cast_if_needed},
index::{get_initializer_name, Index, PouIndexEntry, VariableIndexEntry},
resolver::{AnnotationMap, AstAnnotations, Dependency},
ConfigFormat,
};
use indexmap::IndexSet;
use inkwell::{module::Module, types::BasicTypeEnum, values::GlobalValue};
use inkwell::{module::Module, values::GlobalValue};
use plc_ast::ast::LinkageType;
use plc_diagnostics::diagnostics::Diagnostic;
use std::collections::HashMap;
use std::fs::{read_to_string, write};
use std::path::Path;

use super::{
data_type_generator::get_default_for,
Expand All @@ -24,48 +20,13 @@ use super::{
use crate::codegen::debug::DebugBuilderEnum;
use crate::index::FxIndexSet;

pub fn read_got_layout(location: &str, format: ConfigFormat) -> Result<HashMap<String, u64>, Diagnostic> {
if !Path::new(location).is_file() {
// Assume if the file doesn't exist that there is no existing GOT layout yet. write_got_layout will handle
// creating our file when we want to.
return Ok(HashMap::new());
}

let s =
read_to_string(location).map_err(|_| Diagnostic::new("GOT layout could not be read from file"))?;
match format {
ConfigFormat::JSON => serde_json::from_str(&s)
.map_err(|_| Diagnostic::new("Could not deserialize GOT layout from JSON")),
ConfigFormat::TOML => {
toml::de::from_str(&s).map_err(|_| Diagnostic::new("Could not deserialize GOT layout from TOML"))
}
}
}

pub fn write_got_layout(
got_entries: HashMap<String, u64>,
location: &str,
format: ConfigFormat,
) -> Result<(), Diagnostic> {
let s = match format {
ConfigFormat::JSON => serde_json::to_string(&got_entries)
.map_err(|_| Diagnostic::new("Could not serialize GOT layout to JSON"))?,
ConfigFormat::TOML => toml::ser::to_string(&got_entries)
.map_err(|_| Diagnostic::new("Could not serialize GOT layout to TOML"))?,
};

write(location, s).map_err(|_| Diagnostic::new("GOT layout could not be written to file"))?;
Ok(())
}

pub struct VariableGenerator<'ctx, 'b> {
module: &'b Module<'ctx>,
llvm: &'b Llvm<'ctx>,
global_index: &'b Index,
annotations: &'b AstAnnotations,
types_index: &'b LlvmTypedIndex<'ctx>,
debug: &'b mut DebugBuilderEnum<'ctx>,
got_layout_file: Option<(String, ConfigFormat)>,
}

impl<'ctx, 'b> VariableGenerator<'ctx, 'b> {
Expand All @@ -76,9 +37,8 @@ impl<'ctx, 'b> VariableGenerator<'ctx, 'b> {
annotations: &'b AstAnnotations,
types_index: &'b LlvmTypedIndex<'ctx>,
debug: &'b mut DebugBuilderEnum<'ctx>,
got_layout_file: Option<(String, ConfigFormat)>,
) -> Self {
VariableGenerator { module, llvm, global_index, annotations, types_index, debug, got_layout_file }
VariableGenerator { module, llvm, global_index, annotations, types_index, debug }
}

pub fn generate_global_variables(
Expand Down Expand Up @@ -140,48 +100,6 @@ impl<'ctx, 'b> VariableGenerator<'ctx, 'b> {
);
}

if let Some((location, format)) = &self.got_layout_file {
let got_entries = read_got_layout(location.as_str(), *format)?;
let mut new_globals = Vec::new();
let mut new_got_entries = HashMap::new();
let mut new_got = HashMap::new();

for (name, _) in &globals {
if let Some(idx) = got_entries.get(&name.to_string()) {
new_got_entries.insert(name.to_string(), *idx);
index.associate_got_index(name, *idx);
new_got.insert(*idx, name.to_string());
} else {
new_globals.push(name.to_string());
}
}

// Put any globals that weren't there last time in any free space in the GOT.
let mut idx: u64 = 0;
for name in &new_globals {
while new_got.contains_key(&idx) {
idx += 1;
}
new_got_entries.insert(name.to_string(), idx);
index.associate_got_index(name, idx);
new_got.insert(idx, name.to_string());
}

// Now we can write new_got_entries back out to a file.
write_got_layout(new_got_entries, location.as_str(), *format)?;

// Construct our GOT as a new global array. We initialise this array in the loader code.
let got_size = new_got.keys().max().map_or(0, |m| *m + 1);
let _got = self.llvm.create_global_variable(
self.module,
"__custom_got",
BasicTypeEnum::ArrayType(Llvm::get_array_type(
BasicTypeEnum::PointerType(self.llvm.context.i8_type().ptr_type(0.into())),
got_size.try_into().expect("the computed custom GOT size is too large"),
)),
);
}

Ok(index)
}

Expand Down

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