New warnings when compiling Julia with GCC 12

[giordano]

Since I upgraded to GCC 12, I'm getting some new warnings when compiling Julia.

/home/mose/repo/julia/src/init.c: In function 'jl_init_stack_limits':
/home/mose/repo/julia/src/init.c:75:19: warning: storing the address of local variable 'stacksize' in '*stack_hi' [-Wdangling-pointer=]
   75 |         *stack_hi = (void*)&stacksize;
      |         ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
/home/mose/repo/julia/src/init.c:71:16: note: 'stacksize' declared here
   71 |         size_t stacksize;
      |                ^~~~~~~~~
/home/mose/repo/julia/src/init.c:71:16: note: 'stack_hi' declared here
/home/mose/repo/julia/src/init.c:105:15: warning: storing the address of local variable 'stacksize' in '*stack_lo' [-Wdangling-pointer=]
  105 |     *stack_lo = (void*)((char*)*stack_hi - stacksize);
      |     ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/mose/repo/julia/src/init.c:103:12: note: 'stacksize' declared here
  103 |     size_t stacksize = rl.rlim_cur;
      |            ^~~~~~~~~
/home/mose/repo/julia/src/init.c:103:12: note: 'stack_lo' declared here
/home/mose/repo/julia/src/init.c: In function 'julia_init':
/home/mose/repo/julia/src/init.c:719:21: warning: using a dangling pointer to 'stacksize' [-Wdangling-pointer=]
  719 |     jl_task_t *ct = jl_init_root_task(ptls, stack_lo, stack_hi);
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/mose/repo/julia/src/init.c:103:12: note: 'stacksize' declared here
  103 |     size_t stacksize = rl.rlim_cur;
      |            ^~~~~~~~~

My understanding is that these dangling pointers are there pretty much on purpose. If that's the case, we should use either a pragma or a compiler flag to silence them.

/home/mose/repo/julia/src/gc.c: In function 'gc_mark_stack_resize':
/home/mose/repo/julia/src/gc.c:1722:89: warning: pointer 'old_data' may be used after 'realloc' [-Wuse-after-free]
 1722 |     sp->data = (jl_gc_mark_data_t *)(((char*)sp->data) + (((char*)gc_cache->data_stack) - ((char*)old_data)));
      |                                                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
In file included from /home/mose/repo/julia/src/support/libsupport.h:10,
                 from /home/mose/repo/julia/src/julia.h:14,
                 from /home/mose/repo/julia/src/gc.h:16,
                 from /home/mose/repo/julia/src/gc.c:3:
In function 'realloc_s',
    inlined from 'gc_mark_stack_resize' at /home/mose/repo/julia/src/gc.c:1721:49:
/home/mose/repo/julia/src/support/dtypes.h:356:9: note: call to 'realloc' here
  356 |     p = realloc(p, sz == 0 ? 1 : sz);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/mose/repo/julia/src/gc.c: In function 'gc_mark_stack_resize':
/home/mose/repo/julia/src/gc.c:1726:37: warning: pointer 'pc_stack' may be used after 'realloc' [-Wuse-after-free]
 1726 |     sp->pc = sp->pc_start + (sp->pc - pc_stack);
      |                                     ^
In function 'realloc_s',
    inlined from 'gc_mark_stack_resize' at /home/mose/repo/julia/src/gc.c:1724:49:
/home/mose/repo/julia/src/support/dtypes.h:356:9: note: call to 'realloc' here
  356 |     p = realloc(p, sz == 0 ? 1 : sz);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

This sounds like something that should be fixed? (tentatively pinging @chflood since this is in the GC)

In file included from /home/mose/repo/julia/usr/include/llvm/Bitcode/BitcodeWriter.h:17,
                 from /home/mose/repo/julia/src/aotcompile.cpp:47:
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h: In constructor 'llvm::ModuleSummaryIndex::ModuleSummaryIndex(bool, bool)':
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h:1116:73: warning: member 'llvm::ModuleSummaryIndex::Alloc' is used uninitialized [-Wuninitialized]
 1116 |       : HaveGVs(HaveGVs), EnableSplitLTOUnit(EnableSplitLTOUnit), Saver(Alloc),
      |                                                                         ^~~~~
    [...]
In file included from /home/mose/repo/julia/usr/include/llvm/Bitcode/BitcodeWriter.h:17,
                 from /home/mose/repo/julia/src/jitlayers.cpp:21:
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h: In constructor 'llvm::ModuleSummaryIndex::ModuleSummaryIndex(bool, bool)':
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h:1116:73: warning: member 'llvm::ModuleSummaryIndex::Alloc' is used uninitialized [-Wuninitialized]
 1116 |       : HaveGVs(HaveGVs), EnableSplitLTOUnit(EnableSplitLTOUnit), Saver(Alloc),
      |                                                                         ^~~~~
    [...]
In file included from /home/mose/repo/julia/usr/include/llvm/CodeGen/MachineInstr.h:19,
                 from /home/mose/repo/julia/usr/include/llvm/CodeGen/MachineBasicBlock.h:20,
                 from /home/mose/repo/julia/usr/include/llvm/CodeGen/MachineFunction.h:28,
                 from /home/mose/repo/julia/usr/include/llvm/CodeGen/MachineFunctionPass.h:21,
                 from /home/mose/repo/julia/usr/include/llvm/CodeGen/AsmPrinter.h:22,
                 from /home/mose/repo/julia/src/disasm.cpp:104:
/home/mose/repo/julia/usr/include/llvm/ADT/PointerSumType.h: In static member function 'static llvm::DenseMapInfo<llvm::PointerSumType<TagT, MemberTs ...> >::SumType llvm::DenseMapInfo<llvm::PointerSumType<TagT, MemberTs ...> >::getEmptyKey()':
/home/mose/repo/julia/usr/include/llvm/ADT/PointerSumType.h:275:21: warning: expected 'template' keyword before dependent template name [-Wmissing-template-keyword]
  275 |     return SumType::create<SomeTag>(SomePointerInfo::getEmptyKey());
      |                     ^~~~~~
/home/mose/repo/julia/usr/include/llvm/ADT/PointerSumType.h: In static member function 'static llvm::DenseMapInfo<llvm::PointerSumType<TagT, MemberTs ...> >::SumType llvm::DenseMapInfo<llvm::PointerSumType<TagT, MemberTs ...> >::getTombstoneKey()':
/home/mose/repo/julia/usr/include/llvm/ADT/PointerSumType.h:279:21: warning: expected 'template' keyword before dependent template name [-Wmissing-template-keyword]
  279 |     return SumType::create<SomeTag>(SomePointerInfo::getTombstoneKey());
      |                     ^~~~~~
    [...]
In file included from /home/mose/repo/julia/usr/include/llvm/Bitcode/BitcodeWriter.h:17,
                 from /home/mose/repo/julia/src/codegen.cpp:65:
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h: In constructor 'llvm::ModuleSummaryIndex::ModuleSummaryIndex(bool, bool)':
/home/mose/repo/julia/usr/include/llvm/IR/ModuleSummaryIndex.h:1116:73: warning: member 'llvm::ModuleSummaryIndex::Alloc' is used uninitialized [-Wuninitialized]
 1116 |       : HaveGVs(HaveGVs), EnableSplitLTOUnit(EnableSplitLTOUnit), Saver(Alloc),
      |                                                                         ^~~~~

These are from LLVM, so probably little we can do about directly (Edit 1: first warnings fixed by llvm/llvm-project@8e066b8. Edit 2: more LLVM warnings fixed by llvm/llvm-project@1d9086b).

[giordano]

Not a new warning in GCC 12, but aarch64-linux-gnu builds in CI show this warning:

/cache/build/default-armageddon-0/julialang/julia-master/src/stackwalk.c: In function 'jl_rec_backtrace':
/cache/build/default-armageddon-0/julialang/julia-master/src/stackwalk.c:903:22: warning: initialization of 'mcontext_t *' {aka 'struct sigcontext *'} from incompatible pointer type 'struct unw_sigcontext *' [-Wincompatible-pointer-types]
  903 |     mcontext_t *mc = &c.uc_mcontext;
      |                      ^

Introduced by #45110.

[giordano]

But from the same PR, with GCC 11 on aarch64-linux-gnu I get many more warnings:

/home/mose/repo/julia/src/stackwalk.c: In function 'jl_rec_backtrace':
/home/mose/repo/julia/src/stackwalk.c:903:22: warning: initialization of 'mcontext_t *' from incompatible pointer type 'struct unw_sigcontext *' [-Wincompatible-pointer-types]
  903 |     mcontext_t *mc = &c.uc_mcontext;
      |                      ^
/home/mose/repo/julia/src/stackwalk.c:960:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  960 |     mc->regs[19] = (*mctx)[0];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:961:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  961 |     mc->regs[20] = (*mctx)[1];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:962:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  962 |     mc->regs[21] = (*mctx)[2];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:963:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  963 |     mc->regs[22] = (*mctx)[3];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:964:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  964 |     mc->regs[23] = (*mctx)[4];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:965:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  965 |     mc->regs[24] = (*mctx)[5];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:966:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  966 |     mc->regs[25] = (*mctx)[6];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:967:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  967 |     mc->regs[26] = (*mctx)[7];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:968:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  968 |     mc->regs[27] = (*mctx)[8];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:969:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  969 |     mc->regs[28] = (*mctx)[9];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:970:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  970 |     mc->regs[29] = (*mctx)[10]; // aka fp
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:971:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  971 |     mc->regs[30] = (*mctx)[11]; // aka lr
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:973:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  973 |     mc->sp = (*mctx)[13];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:974:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  974 |     mcfp->vregs[7] = (*mctx)[14]; // aka d8
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:975:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  975 |     mcfp->vregs[8] = (*mctx)[15]; // aka d9
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:976:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  976 |     mcfp->vregs[9] = (*mctx)[16]; // aka d10
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:977:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  977 |     mcfp->vregs[10] = (*mctx)[17]; // aka d11
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:978:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  978 |     mcfp->vregs[11] = (*mctx)[18]; // aka d12
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:979:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  979 |     mcfp->vregs[12] = (*mctx)[19]; // aka d13
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:980:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  980 |     mcfp->vregs[13] = (*mctx)[20]; // aka d14
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:981:9: warning: array subscript 'unw_fpsimd_context_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  981 |     mcfp->vregs[14] = (*mctx)[21]; // aka d15
      |         ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:983:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  983 |     mc->sp = ptr_demangle(mc->sp);
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:984:35: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  984 |     mc->regs[30] = ptr_demangle(mc->regs[30]);
      |                                   ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:984:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  984 |     mc->regs[30] = ptr_demangle(mc->regs[30]);
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^
/home/mose/repo/julia/src/stackwalk.c:985:7: warning: array subscript 'mcontext_t[0]' is partly outside array bounds of 'bt_context_t[1]' {aka 'unw_tdep_context_t[1]'} [-Warray-bounds]
  985 |     mc->pc = mc->regs[30];
      |       ^~
/home/mose/repo/julia/src/stackwalk.c:899:18: note: while referencing 'c'
  899 |     bt_context_t c;
      |                  ^

CC: @vtjnash

[giordano]

On 0a26e90 julia builds cleanly on x86_64-linux-gnu with gcc 12.3. There are still some warnings on aarch64-linux-gnu, but I think it's time to close this ticket because it served its purpose, maybe I'll open something more specific later for aarch64-linux-gnu.