On Sun, 22 May 2022 16:45:11 GMT, Kim Barrett <kbarr...@openjdk.org> wrote:
>> It might be GCC bug... >> >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578 >> >> This issue is for integer literal, but [Comment >> 29](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578#c29) mentions address >> calculation (e.g. `NULL + offset`) - it is similar the problem in >> jfrTraceIdBits.inline.hp because `dest` comes from `low_addr()` (`addr + >> low_offset`). > > I don't see the similarity. That gcc bug is about literals used as addresses, > which get treated (suggested inappropriately) as NULL+offset, with NULL+offset > being a cause of warnings. I don't see that happening in our case. That is, > in our `addr + low_offset`, `addr` doesn't seem to be either a literal or NULL > that I can see. > > It's hard for me to investigate this any further just by perusing the code, so > I'm in the process of getting set up to build with gcc12.x. That will let me > do some experiments. It may take me a few days to get to that point though. I spent some time looking into this one. I agree there is a false positive here, and there doesn't seem to be a better solution than suppressing the warning. I would prefer the change below, rather than what's proposed. Also eliminate the changes to utilities/compilerWarnings files. This is a very gcc-specific issue; there's no reason to generalize the solution. The reason for relocating the suppression is to be able to describe the issue in more detail in a context where that description makes sense. template <typename T> inline void JfrTraceIdBits::store(jbyte bits, const T* ptr) { assert(ptr != NULL, "invariant"); // gcc12 warns "writing 1 byte into a region of size 0" when T == Klass. // The warning seems to be a false positive. And there is no warning for // other types that use the same mechanisms. The warning also sometimes // goes away with minor code perturbations, such as replacing function calls // with equivalent code directly inlined. PRAGMA_DIAG_PUSH PRAGMA_DISABLE_GCC_WARNING("-Wstringop-overflow") set(bits, traceid_tag_byte(ptr)); PRAGMA_DIAG_POP } ------------- PR: https://git.openjdk.java.net/jdk/pull/8646
