diff --git a/Cargo.lock b/Cargo.lock
index b984e66531e..3786a94b241 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -56,18 +56,18 @@ dependencies = [
 
 [[package]]
 name = "gccjit"
-version = "3.3.0"
+version = "3.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "26b73d18b642ce16378af78f89664841d7eeafa113682ff5d14573424eb0232a"
+checksum = "8b2c6ee720b5459292678267e9ffed8229b11e0e27fc5ecf7618634dc6272fa4"
 dependencies = [
  "gccjit_sys",
 ]
 
 [[package]]
 name = "gccjit_sys"
-version = "1.3.0"
+version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ee689456c013616942d5aef9a84d613cefcc3b335340d036f3650fc1a7459e15"
+checksum = "0cea2ed05e093fd90bd21fa03a7d09e07f62103ce94de21859f048c9a6c18e42"
 dependencies = [
  "libc",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 8956bd69489..aba88456801 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,7 @@ default = ["master"]
 [dependencies]
 object = { version = "0.37.0", default-features = false, features = ["std", "read"] }
 tempfile = "3.20"
-gccjit = { version = "3.3.0", features = ["dlopen"] }
+gccjit = { version = "3.4.0", features = ["dlopen"] }
 #gccjit = { git = "https://github.com/rust-lang/gccjit.rs", branch = "error-dlopen", features = ["dlopen"] }
 
 # Local copy.
diff --git a/src/builder.rs b/src/builder.rs
index a9287d3247a..9eca9eeb620 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -4,8 +4,8 @@ use std::convert::TryFrom;
 use std::ops::Deref;
 
 use gccjit::{
-    BinaryOp, Block, ComparisonOp, Context, Function, LValue, Location, RValue, ToRValue, Type,
-    UnaryOp,
+    BinaryOp, Block, CType, ComparisonOp, Context, Function, LValue, Location, RValue, ToRValue,
+    Type, UnaryOp,
 };
 use rustc_abi as abi;
 use rustc_abi::{Align, HasDataLayout, Size, TargetDataLayout, WrappingRange};
@@ -1513,8 +1513,10 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         variable.to_rvalue()
     }
 
-    fn va_arg(&mut self, _list: RValue<'gcc>, _ty: Type<'gcc>) -> RValue<'gcc> {
-        unimplemented!();
+    fn va_arg(&mut self, list: RValue<'gcc>, ty: Type<'gcc>) -> RValue<'gcc> {
+        let va_list_type = self.context.new_c_type(CType::VaList);
+        let list = self.context.new_cast(self.location, list, va_list_type.make_pointer());
+        self.context.new_va_arg(self.location, list, ty)
     }
 
     #[cfg(feature = "master")]
diff --git a/src/intrinsic/mod.rs b/src/intrinsic/mod.rs
index ff8312beb36..76a868e0fad 100644
--- a/src/intrinsic/mod.rs
+++ b/src/intrinsic/mod.rs
@@ -4,7 +4,7 @@ mod simd;
 #[cfg(feature = "master")]
 use std::iter;
 
-use gccjit::{ComparisonOp, Function, FunctionType, RValue, ToRValue, Type, UnaryOp};
+use gccjit::{CType, ComparisonOp, Function, FunctionType, RValue, ToRValue, Type, UnaryOp};
 use rustc_abi::{Align, BackendRepr, HasDataLayout, WrappingRange};
 use rustc_codegen_ssa::base::wants_msvc_seh;
 use rustc_codegen_ssa::common::IntPredicate;
@@ -362,7 +362,9 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
                 unimplemented!();
             }
             sym::va_arg => {
-                unimplemented!();
+                let va_list = args[0].immediate();
+                let gcc_type = self.immediate_backend_type(result.layout);
+                self.va_arg(va_list, gcc_type)
             }
 
             sym::volatile_load | sym::unaligned_volatile_load => {
@@ -691,8 +693,18 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
         self.context.new_rvalue_from_int(self.int_type, 0)
     }
 
-    fn va_start(&mut self, _va_list: RValue<'gcc>) {
-        unimplemented!();
+    fn va_start(&mut self, va_list: RValue<'gcc>) {
+        let func = self.context.get_builtin_function("__builtin_va_start");
+
+        let va_list_type = self.context.new_c_type(CType::VaList);
+        let va_list = self.context.new_cast(self.location, va_list, va_list_type.make_pointer());
+
+        // Pre-C23 requires that the last "normal" argument was passed to va_start.
+        // Just pass 0, this appears to be handled correctly.
+        let last_normal_arg = self.context.new_rvalue_from_int(self.int_type, 0);
+
+        let call = self.context.new_call(self.location, func, &[va_list, last_normal_arg]);
+        self.block.add_eval(self.location, call);
     }
 
     fn retag_reg(&mut self, _ptr: Self::Value, _info: &RetagInfo<Self::Value>) -> Self::Value {
diff --git a/tests/failing-ui-tests.txt b/tests/failing-ui-tests.txt
index a1397746b73..bf274f2c781 100644
--- a/tests/failing-ui-tests.txt
+++ b/tests/failing-ui-tests.txt
@@ -74,9 +74,6 @@ tests/ui/linkage-attr/raw-dylib/elf/glibc-x86_64.rs
 tests/ui/explicit-tail-calls/recursion-etc.rs
 tests/ui/explicit-tail-calls/indexer.rs
 tests/ui/explicit-tail-calls/drop-order.rs
-tests/ui/c-variadic/valid.rs
-tests/ui/c-variadic/inherent-method.rs
-tests/ui/c-variadic/trait-method.rs
 tests/ui/explicit-tail-calls/become-cast-return.rs
 tests/ui/explicit-tail-calls/become-indirect-return.rs
 tests/ui/panics/panic-abort-backtrace-without-debuginfo.rs
@@ -97,15 +94,12 @@ tests/ui/eii/linking/same-symbol.rs
 tests/ui/eii/privacy1.rs
 tests/ui/eii/default/call_impl.rs
 tests/ui/eii/linking/track_caller_cross_crate.rs
-tests/ui/c-variadic/copy.rs
 tests/ui/asm/x86_64/global_asm_escape.rs
 tests/ui/lto/all-crates.rs
-tests/ui/consts/const-eval/c-variadic.rs
 tests/ui/eii/default/call_default_panics.rs
 tests/ui/explicit-tail-calls/indirect.rs
 tests/ui/traits/inheritance/self-in-supertype.rs
 tests/ui/fmt/fmt_debug/shallow.rs
-tests/ui/c-variadic/roundtrip.rs
 tests/ui/eii/eii_impl_with_contract.rs
 tests/ui/eii/static/cross_crate_decl.rs
 tests/ui/eii/static/cross_crate_def.rs