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libobs-d3d11: Add checksum to shader cache

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A few reports came in of cache files with the correct size but full of
null bytes, presumably from a system crash and an SSD lying about buffer
flushes. This commit adds a checksum at the end of the compiled bytecode
so we don't try to use invalid data.

Co-Authored-By: derrod <dennis@obsproject.com>
This commit is contained in:
Richard Stanway 2023-11-15 21:01:19 +01:00 committed by Lain
parent 9f66c23825
commit 1641812580
1 changed files with 60 additions and 12 deletions
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72
libobs-d3d11/d3d11-shader.cpp
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@ -206,13 +206,13 @@ void gs_shader::BuildConstantBuffer()
gs_shader_set_default(&params[i]);
}
static uint64_t fnv1a_hash(const char *str)
static uint64_t fnv1a_hash(const char *str, size_t len)
{
const uint64_t FNV_OFFSET = 14695981039346656037ULL;
const uint64_t FNV_PRIME = 1099511628211ULL;
uint64_t hash = FNV_OFFSET;
while (*str) {
hash ^= (uint64_t)*str++;
for (size_t i = 0; i < len; i++) {
hash ^= (uint64_t)str[i];
hash *= FNV_PRIME;
}
return hash;
@ -224,31 +224,64 @@ void gs_shader::Compile(const char *shaderString, const char *file,
ComPtr<ID3D10Blob> errorsBlob;
HRESULT hr;
bool is_cached = false;
char hashstr[20];
if (!shaderString)
throw "No shader string specified";
uint64_t hash = fnv1a_hash(shaderString);
size_t shaderStrLen = strlen(shaderString);
uint64_t hash = fnv1a_hash(shaderString, shaderStrLen);
snprintf(hashstr, sizeof(hashstr), "%02llx", hash);
BPtr program_data =
os_get_program_data_path_ptr("obs-studio/shader-cache");
auto cachePath = filesystem::u8path(program_data.Get()) / hashstr;
// Increment if on-disk format changes
cachePath += ".v2";
std::fstream cacheFile;
cacheFile.exceptions(fstream::badbit | fstream::eofbit);
if (filesystem::exists(cachePath) && !filesystem::is_empty(cachePath))
cacheFile.open(cachePath, ios::in | ios::binary | ios::ate);
if (cacheFile.is_open()) {
streampos len = cacheFile.tellg();
cacheFile.seekg(0, ios::beg);
uint64_t checksum;
D3DCreateBlob(len, shader);
cacheFile.read((char *)(*shader)->GetBufferPointer(), len);
} else {
hr = D3DCompile(shaderString, strlen(shaderString), file, NULL,
NULL, "main", target,
try {
streampos len = cacheFile.tellg();
// Not enough data for checksum + shader
if (len <= sizeof(checksum))
throw length_error("File truncated");
cacheFile.seekg(0, ios::beg);
len -= sizeof(checksum);
D3DCreateBlob(len, shader);
cacheFile.read((char *)(*shader)->GetBufferPointer(),
len);
uint64_t calculated_checksum = fnv1a_hash(
(char *)(*shader)->GetBufferPointer(), len);
cacheFile.read((char *)&checksum, sizeof(checksum));
if (calculated_checksum != checksum)
throw exception("Checksum mismatch");
is_cached = true;
} catch (const exception &e) {
// Something went wrong reading the cache file, delete it
blog(LOG_WARNING,
"Loading shader cache file failed with \"%s\": %s",
e.what(), file);
cacheFile.close();
filesystem::remove(cachePath);
}
}
if (!is_cached) {
hr = D3DCompile(shaderString, shaderStrLen, file, NULL, NULL,
"main", target,
D3D10_SHADER_OPTIMIZATION_LEVEL3, 0, shader,
errorsBlob.Assign());
if (FAILED(hr)) {
@ -260,8 +293,23 @@ void gs_shader::Compile(const char *shaderString, const char *file,
cacheFile.open(cachePath, ios::out | ios::binary);
if (cacheFile.is_open()) {
cacheFile.write((char *)(*shader)->GetBufferPointer(),
try {
uint64_t calculated_checksum = fnv1a_hash(
(char *)(*shader)->GetBufferPointer(),
(*shader)->GetBufferSize());
cacheFile.write(
(char *)(*shader)->GetBufferPointer(),
(*shader)->GetBufferSize());
cacheFile.write((char *)&calculated_checksum,
sizeof(calculated_checksum));
} catch (const exception &e) {
blog(LOG_WARNING,
"Writing shader cache file failed with \"%s\": %s",
e.what(), file);
cacheFile.close();
filesystem::remove(cachePath);
}
}
}