Merge pull request #7348 from thufschmitt/dont-use-vlas

Remove the usage of VLAs in the code

(cherry picked from commit ac4431e9d016e62fb5dc9ae36833bd0c6cdadeec)
Change-Id: Ifbf5fbfc2e27122362a2aaea4b62c7cf3ca46b1a
This commit is contained in:
eldritch horrors 2024-03-04 05:51:23 +01:00
parent 30f3298e9d
commit 5e182235cb
8 changed files with 78 additions and 33 deletions

View file

@ -1,6 +1,7 @@
#include "eval.hh"
#include "eval-settings.hh"
#include "hash.hh"
#include "primops.hh"
#include "types.hh"
#include "util.hh"
#include "store-api.hh"
@ -38,6 +39,7 @@
#include <boost/coroutine2/coroutine.hpp>
#include <boost/coroutine2/protected_fixedsize_stack.hpp>
#include <boost/context/stack_context.hpp>
#include <boost/container/small_vector.hpp>
#endif
@ -703,6 +705,23 @@ void EvalState::addConstant(const std::string & name, Value * v, Constant info)
}
void PrimOp::check()
{
if (arity > maxPrimOpArity) {
throw Error("primop arity must not exceed %1%", maxPrimOpArity);
}
}
void Value::mkPrimOp(PrimOp * p)
{
p->check();
clearValue();
internalType = tPrimOp;
primOp = p;
}
Value * EvalState::addPrimOp(PrimOp && primOp)
{
/* Hack to make constants lazy: turn them into a application of
@ -1683,7 +1702,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
/* We have all the arguments, so call the primop with
the previous and new arguments. */
Value * vArgs[arity];
Value * vArgs[maxPrimOpArity];
auto n = argsDone;
for (Value * arg = &vCur; arg->isPrimOpApp(); arg = arg->primOpApp.left)
vArgs[--n] = arg->primOpApp.right;
@ -1740,11 +1759,17 @@ void ExprCall::eval(EvalState & state, Env & env, Value & v)
Value vFun;
fun->eval(state, env, vFun);
Value * vArgs[args.size()];
// Empirical arity of Nixpkgs lambdas by regex e.g. ([a-zA-Z]+:(\s|(/\*.*\/)|(#.*\n))*){5}
// 2: over 4000
// 3: about 300
// 4: about 60
// 5: under 10
// This excluded attrset lambdas (`{...}:`). Contributions of mixed lambdas appears insignificant at ~150 total.
boost::container::small_vector<Value *, 4> vArgs(args.size());
for (size_t i = 0; i < args.size(); ++i)
vArgs[i] = args[i]->maybeThunk(state, env);
state.callFunction(vFun, args.size(), vArgs, v, pos);
state.callFunction(vFun, args.size(), vArgs.data(), v, pos);
}
@ -1983,8 +2008,8 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
return result;
};
Value values[es->size()];
Value * vTmpP = values;
boost::container::small_vector<Value, conservativeStackReservation> values(es->size());
Value * vTmpP = values.data();
for (auto & [i_pos, i] : *es) {
Value & vTmp = *vTmpP++;

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@ -18,6 +18,12 @@
namespace nix {
/**
* We put a limit on primop arity because it lets us use a fixed size array on
* the stack. 8 is already an impractical number of arguments. Use an attrset
* argument for such overly complicated functions.
*/
constexpr size_t maxPrimOpArity = 8;
class Store;
class EvalState;
@ -69,6 +75,12 @@ struct PrimOp
* Optional experimental for this to be gated on.
*/
std::optional<ExperimentalFeature> experimentalFeature;
/**
* Validity check to be performed by functions that introduce primops,
* such as RegisterPrimOp() and Value::mkPrimOp().
*/
void check();
};
/**

View file

@ -28,7 +28,6 @@
#include <cmath>
namespace nix {
@ -2547,6 +2546,7 @@ static void prim_removeAttrs(EvalState & state, const PosIdx pos, Value * * args
/* Get the attribute names to be removed.
We keep them as Attrs instead of Symbols so std::set_difference
can be used to remove them from attrs[0]. */
// 64: large enough to fit the attributes of a derivation
boost::container::small_vector<Attr, 64> names;
names.reserve(args[1]->listSize());
for (auto elem : args[1]->listItems()) {
@ -2726,8 +2726,8 @@ static void prim_catAttrs(EvalState & state, const PosIdx pos, Value * * args, V
auto attrName = state.symbols.create(state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.catAttrs"));
state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.catAttrs");
Value * res[args[1]->listSize()];
unsigned int found = 0;
boost::container::small_vector<Value *, nonRecursiveStackReservation> res(args[1]->listSize());
size_t found = 0;
for (auto v2 : args[1]->listItems()) {
state.forceAttrs(*v2, pos, "while evaluating an element in the list passed as second argument to builtins.catAttrs");
@ -3061,9 +3061,8 @@ static void prim_filter(EvalState & state, const PosIdx pos, Value * * args, Val
state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.filter");
// FIXME: putting this on the stack is risky.
Value * vs[args[1]->listSize()];
unsigned int k = 0;
boost::container::small_vector<Value *, nonRecursiveStackReservation> vs(args[1]->listSize());
size_t k = 0;
bool same = true;
for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
@ -3188,10 +3187,14 @@ static void anyOrAll(bool any, EvalState & state, const PosIdx pos, Value * * ar
state.forceFunction(*args[0], pos, std::string("while evaluating the first argument passed to builtins.") + (any ? "any" : "all"));
state.forceList(*args[1], pos, std::string("while evaluating the second argument passed to builtins.") + (any ? "any" : "all"));
std::string_view errorCtx = any
? "while evaluating the return value of the function passed to builtins.any"
: "while evaluating the return value of the function passed to builtins.all";
Value vTmp;
for (auto elem : args[1]->listItems()) {
state.callFunction(*args[0], *elem, vTmp, pos);
bool res = state.forceBool(vTmp, pos, std::string("while evaluating the return value of the function passed to builtins.") + (any ? "any" : "all"));
bool res = state.forceBool(vTmp, pos, errorCtx);
if (res == any) {
v.mkBool(any);
return;
@ -3447,7 +3450,7 @@ static void prim_concatMap(EvalState & state, const PosIdx pos, Value * * args,
state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.concatMap");
auto nrLists = args[1]->listSize();
Value lists[nrLists];
boost::container::small_vector<Value, conservativeStackReservation> lists(nrLists);
size_t len = 0;
for (unsigned int n = 0; n < nrLists; ++n) {

View file

@ -8,6 +8,22 @@
namespace nix {
/**
* For functions where we do not expect deep recursion, we can use a sizable
* part of the stack a free allocation space.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t nonRecursiveStackReservation = 128;
/**
* Functions that maybe applied to self-similar inputs, such as concatMap on a
* tree, should reserve a smaller part of the stack for allocation.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t conservativeStackReservation = 16;
struct RegisterPrimOp
{
typedef std::vector<PrimOp> PrimOps;

View file

@ -349,13 +349,7 @@ public:
// Value will be overridden anyways
}
inline void mkPrimOp(PrimOp * p)
{
clearValue();
internalType = tPrimOp;
primOp = p;
}
void mkPrimOp(PrimOp * p);
inline void mkPrimOpApp(Value * l, Value * r)
{

View file

@ -152,11 +152,10 @@ StorePath writeDerivation(Store & store,
/* Read string `s' from stream `str'. */
static void expect(std::istream & str, std::string_view s)
{
char s2[s.size()];
str.read(s2, s.size());
std::string_view s2View { s2, s.size() };
if (s2View != s)
throw FormatError("expected string '%s', got '%s'", s, s2View);
for (auto & c : s) {
if (str.get() != c)
throw FormatError("expected string '%1%'", s);
}
}

View file

@ -323,9 +323,7 @@ typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots
static void readProcLink(const std::string & file, UncheckedRoots & roots)
{
/* 64 is the starting buffer size gnu readlink uses... */
auto bufsiz = ssize_t{64};
try_again:
constexpr auto bufsiz = PATH_MAX;
char buf[bufsiz];
auto res = readlink(file.c_str(), buf, bufsiz);
if (res == -1) {
@ -334,10 +332,7 @@ try_again:
throw SysError("reading symlink");
}
if (res == bufsiz) {
if (SSIZE_MAX / 2 < bufsiz)
throw Error("stupidly long symlink");
bufsiz *= 2;
goto try_again;
throw Error("overly long symlink starting with '%1%'", std::string_view(buf, bufsiz));
}
if (res > 0 && buf[0] == '/')
roots[std::string(static_cast<char *>(buf), res)]

View file

@ -114,7 +114,8 @@ TEST_F(ValuePrintingTests, vLambda)
TEST_F(ValuePrintingTests, vPrimOp)
{
Value vPrimOp;
vPrimOp.mkPrimOp(nullptr);
PrimOp primOp{};
vPrimOp.mkPrimOp(&primOp);
test(vPrimOp, "<PRIMOP>");
}