hal: Introduce cstr_from_bytes_until_nul helper function.

Remove a handful of `unsafe` blocks from the Vulkan back end.

CHANGELOG.md

@@ -59,7 +59,7 @@ Bottom level categories:
 
 #### Vulkan
 
-- Don't use a pointer to a local copy of a `PhysicalDeviceDriverProperties` struct after it has gone out of scope. In fact, don't make a local copy at all. By @jimblandy in [#3076](https://github.com/gfx-rs/wgpu/pull/3076).
+- Don't use a pointer to a local copy of a `PhysicalDeviceDriverProperties` struct after it has gone out of scope. In fact, don't make a local copy at all. Introduce a helper function for building `CStr`s from C character arrays, and remove some `unsafe` blocks. By @jimblandy in [#3076](https://github.com/gfx-rs/wgpu/pull/3076).
 
 ## wgpu-0.14.0 (2022-10-05)
 

wgpu-hal/src/auxil/mod.rs

@@ -115,3 +115,24 @@ impl crate::TextureCopy {
  self.size = self.size.min(&max_src_size).min(&max_dst_size);
  }
 }
+
+/// Construct a `CStr` from a byte slice, up to the first zero byte.
+///
+/// Return a `CStr` extending from the start of `bytes` up to and
+/// including the first zero byte. If there is no zero byte in
+/// `bytes`, return `None`.
+///
+/// This can be removed when `CStr::from_bytes_until_nul` is stabilized.
+/// ([#95027](https://github.com/rust-lang/rust/issues/95027))
+#[allow(dead_code)]
+pub(crate) fn cstr_from_bytes_until_nul(bytes: &[std::ffi::c_char]) -> Option<&std::ffi::CStr> {
+ if bytes.contains(&0) {
+ // Safety for `CStr::from_ptr`:
+ // - We've ensured that the slice does contain a null terminator.
+ // - The range is valid to read, because the slice covers it.
+ // - The memory won't be changed, because the slice borrows it.
+ unsafe { Some(std::ffi::CStr::from_ptr(bytes.as_ptr())) }
+ } else {
+ None
+ }
+}

wgpu-hal/src/vulkan/adapter.rs

@@ -538,9 +538,10 @@ impl PhysicalDeviceCapabilities {
  }
 
  pub fn supports_extension(&self, extension: &CStr) -> bool {
+ use crate::auxil::cstr_from_bytes_until_nul;
  self.supported_extensions
  .iter()
- .any(|ep| unsafe { CStr::from_ptr(ep.extension_name.as_ptr()) } == extension)
+ .any(|ep| cstr_from_bytes_until_nul(&ep.extension_name) == Some(extension))
  }
 
  /// Map `requested_features` to the list of Vulkan extension strings required to create the logical device.
@@ -885,14 +886,15 @@ impl super::Instance {
  &self,
  phd: vk::PhysicalDevice,
  ) -> Option<crate::ExposedAdapter<super::Api>> {
+ use crate::auxil::cstr_from_bytes_until_nul;
  use crate::auxil::db;
 
  let (phd_capabilities, phd_features) = self.shared.inspect(phd);
 
  let info = wgt::AdapterInfo {
- name: unsafe {
- CStr::from_ptr(phd_capabilities.properties.device_name.as_ptr())
- .to_str()
+ name: {
+ cstr_from_bytes_until_nul(&phd_capabilities.properties.device_name)
+ .and_then(|info| info.to_str().ok())
  .unwrap_or("?")
  .to_owned()
  },
@@ -906,23 +908,23 @@ impl super::Instance {
  ash::vk::PhysicalDeviceType::CPU => wgt::DeviceType::Cpu,
  _ => wgt::DeviceType::Other,
  },
- driver: unsafe {
- let driver_name = if let Some(ref driver) = phd_capabilities.driver {
- CStr::from_ptr(driver.driver_name.as_ptr()).to_str().ok()
- } else {
- None
- };
-
- driver_name.unwrap_or("?").to_owned()
+ driver: {
+ phd_capabilities
+ .driver
+  .as_ref()
+ .and_then(|driver| cstr_from_bytes_until_nul(&driver.driver_name))
+  .and_then(|name| name.to_str().ok())
+ .unwrap_or("?")
+  .to_owned()
  },
- driver_info: unsafe {
- let driver_info = if let Some(ref driver) = phd_capabilities.driver {
- CStr::from_ptr(driver.driver_info.as_ptr()).to_str().ok()
- } else {
- None
- };
-
- driver_info.unwrap_or("?").to_owned()
+ driver_info: {
+ phd_capabilities
+ .driver
+  .as_ref()
+ .and_then(|driver| cstr_from_bytes_until_nul(&driver.driver_info))
+  .and_then(|name| name.to_str().ok())
+ .unwrap_or("?")
+  .to_owned()
  },
  backend: wgt::Backend::Vulkan,
  };

wgpu-hal/src/vulkan/instance.rs

@@ -201,10 +201,9 @@ impl super::Instance {
 
  // Only keep available extensions.
  extensions.retain(|&ext| {
- if instance_extensions
- .iter()
- .any(|inst_ext| unsafe { CStr::from_ptr(inst_ext.extension_name.as_ptr()) == ext })
- {
+ if instance_extensions.iter().any(|inst_ext| {
+ crate::auxil::cstr_from_bytes_until_nul(&inst_ext.extension_name) == Some(ext)
+ }) {
  true
  } else {
  log::info!("Unable to find extension: {}", ext.to_string_lossy());
@@ -483,6 +482,8 @@ impl Drop for super::InstanceShared {
 
 impl crate::Instance<super::Api> for super::Instance {
  unsafe fn init(desc: &crate::InstanceDescriptor) -> Result<Self, crate::InstanceError> {
+ use crate::auxil::cstr_from_bytes_until_nul;
+
  let entry = match ash::Entry::load() {
  Ok(entry) => entry,
  Err(err) => {
@@ -531,9 +532,9 @@ impl crate::Instance<super::Api> for super::Instance {
  })?;
 
  let nv_optimus_layer = CStr::from_bytes_with_nul(b"VK_LAYER_NV_optimus\0").unwrap();
- let has_nv_optimus = instance_layers
- .iter()
-  .any(|inst_layer| CStr::from_ptr(inst_layer.layer_name.as_ptr()) == nv_optimus_layer);
+ let has_nv_optimus = instance_layers.iter().any(|inst_layer| {
+ cstr_from_bytes_until_nul(&inst_layer.layer_name) == Some(nv_optimus_layer)
+ });
 
  // Check requested layers against the available layers
  let layers = {
@@ -544,10 +545,9 @@ impl crate::Instance<super::Api> for super::Instance {
 
  // Only keep available layers.
  layers.retain(|&layer| {
- if instance_layers
- .iter()
- .any(|inst_layer| CStr::from_ptr(inst_layer.layer_name.as_ptr()) == layer)
- {
+ if instance_layers.iter().any(|inst_layer| {
+ cstr_from_bytes_until_nul(&inst_layer.layer_name) == Some(layer)
+ }) {
  true
  } else {
  log::warn!("Unable to find layer: {}", layer.to_string_lossy());