compiler: use SHA1-hash for symname for long gcbits symbols
The current scheme used by the compiler for "gcbits" symbols involves
generating a symbol name based on a 32-char encoding of the bits data.
This scheme works well in most cases but can generate very long symbol
names in rare cases. To help avoid such long symbol names, switch to a
different encoding scheme based on the SHA1 digest of the payload if
the symbol size would be too large.
Fixes golang/go#32083.
Change-Id: If7db420e96b0ff280593fdcb36ebb626cacc91af
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/177598
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/go/types.cc b/go/types.cc
index 5260626..f6c104c 100644
--- a/go/types.cc
+++ b/go/types.cc
@@ -12,6 +12,7 @@
#include "gogo.h"
#include "go-diagnostics.h"
#include "go-encode-id.h"
+#include "go-sha1.h"
#include "operator.h"
#include "expressions.h"
#include "statements.h"
@@ -2776,22 +2777,43 @@
}
}
-// Return a symbol name for this ptrmask. This is used to coalesce
-// identical ptrmasks, which are common. The symbol name must use
-// only characters that are valid in symbols. It's nice if it's
-// short. We convert it to a string that uses only 32 characters,
-// avoiding digits and u and U.
-
+// Return a symbol name for this ptrmask. This is used to coalesce identical
+// ptrmasks, which are common. The symbol name must use only characters that are
+// valid in symbols. It's nice if it's short. For smaller ptrmasks, we convert
+// it to a string that uses only 32 characters, avoiding digits and u and U. For
+// longer pointer masks, apply the same process to the SHA1 digest of the bits,
+// so as to avoid pathologically long symbol names (see related Go issues #32083
+// and #11583 for more on this). To avoid collisions between the two encoding
+// schemes, use a prefix ("X") for the SHA form to disambiguate.
std::string
Ptrmask::symname() const
{
+ const std::vector<unsigned char>* bits(&this->bits_);
+ std::vector<unsigned char> shabits;
+ std::string prefix;
+
+ if (this->bits_.size() > 128)
+ {
+ // Produce a SHA1 digest of the data.
+ Go_sha1_helper* sha1_helper = go_create_sha1_helper();
+ sha1_helper->process_bytes(&this->bits_[0], this->bits_.size());
+ std::string digest = sha1_helper->finish();
+ delete sha1_helper;
+
+ // Redirect the bits vector to the digest, and update the prefix.
+ prefix = "X";
+ for (char c : digest)
+ shabits.push_back((unsigned char) c);
+ bits = &shabits;
+ }
+
const char chars[33] = "abcdefghijklmnopqrstvwxyzABCDEFG";
go_assert(chars[32] == '\0');
- std::string ret;
+ std::string ret(prefix);
unsigned int b = 0;
int remaining = 0;
- for (std::vector<unsigned char>::const_iterator p = this->bits_.begin();
- p != this->bits_.end();
+ for (std::vector<unsigned char>::const_iterator p = bits->begin();
+ p != bits->end();
++p)
{
b |= *p << remaining;
