[sanitizer_common] Don't try to unmap unaligned memory

[ro]

Summary

Enabling sanitizer_common tests on Solaris (D91606) and SPARC (D91608) uncovered a sparcv9 failure

SanitizerCommon-Unit :: ./Sanitizer-sparcv9-Test/CompactRingBuffer.int64

like this:

[ RUN      ] CompactRingBuffer.int64
==24576==ERROR: SanitizerTool failed to deallocate 0x2000 (8192) bytes at address 0xffffffff7f59b000
==24576==Sanitizer CHECK failed: /vol/llvm/src/llvm-project/local/compiler-rt/lib/sanitizer_common/sanitizer_posix.cpp:61 (("unable to unmap" && 0)) != (0) (0, 0)

The problemis that the original allocation via MmapAlignedOrDieOnFatalError is for 4 kB, but the Solaris/sparcv9 pagesize is 8 kB. So the initial allocation is for 12 kB, rounded to a multiple of the pagesize. Afterwards, the unneeded rest is unmapped again, but this fails since the address is not pagesize-aligned.

This patch avoids this by only unmapping correctly aligned memory.

The patch still FAILs, but for a different reason, and this part of the issue is generic.

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_posix.cpp

95

map_res is just from MMap, it must be aligned?

99

probably better to align end up to the pagesize

[ro]

Sorry for dropping the ball on this one: the revised patch is trivial. I've now tested it (together with D91827 which is necessary to make the test PASS) on sparcv9-sun-solaris2.11, amd64-pc-solaris2.11, and x86_64-pc-linux-gnu.

compiler-rt/lib/sanitizer_common/sanitizer_posix.cpp

95

It is indeed: this snippet is unnecessary.

99

Right, patch amended accordingly.

[ro]

Incorporate review comments.

compiler-rt/lib/sanitizer_common/sanitizer_posix.cpp

void *MmapAlignedOrDieOnFatalError(uptr size, uptr alignment,
   uptr map_size = size + alignment;
   uptr map_res = (uptr)MmapOrDieOnFatalError(map_size, mem_type);
   if (UNLIKELY(!map_res))
     return nullptr;
   uptr map_end = map_res + map_size;
   uptr res = map_res;
   if (!IsAligned(res, alignment)) {
     res = (map_res + alignment - 1) & ~(alignment - 1);
     UnmapOrDie((void*)map_res, res - map_res);
   }
   uptr end = res + size;
+  end = RoundUpTo(end, GetPageSizeCached());
   if (end != map_end)
     UnmapOrDie((void*)end, map_end - end);
   return (void*)res;
 }
 
 void *MmapNoReserveOrDie(uptr size, const char *mem_type) {
   size = RoundUpTo(size, GetPageSizeCached());
   uptr p = MmapNamed(nullptr, size, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANON | MAP_NORESERVE, mem_type);