http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55644
Matt Hargett <matt at use dot net> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|bootstrap-lto fails on |maybe-uninitialized false
|current trunk (with and |positive
|without profiledbootstrap) |
--- Comment #11 from Matt Hargett <matt at use dot net> 2013-03-01 23:34:53 UTC
---
The current false positives emitted:
mhargett@chert:/work/mhargett/gcc-trunk-lto-O3-debug/gcc$
/work/mhargett/gcc-trunk-lto-O3-debug/./prev-gcc/xg++
-B/work/mhargett/gcc-trunk-lto-O3-debug/./prev-gcc/
-B/u/mhargett/x86_64-unknown-linux-gnu/bin/ -nostdinc++
-B/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs
-B/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/.libs
-I/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/include/x86_64-unknown-linux-gnu
-I/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/include
-I/work/mhargett/gcc-trunk/libstdc++-v3/libsupc++
-L/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs
-L/work/mhargett/gcc-trunk-lto-O3-debug/prev-x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/.libs
-O3 -g -flto=jobserver -flto-partition=none -frandom-seed=1 -gtoggle -DIN_GCC
-fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall
-Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribute -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror -fno-common
-DHAVE_CONFIG_H -static-libstdc++ -static-libgcc gcov-dump.o
libcommon.a ../libcpp/libcpp.a ../libbacktrace/.libs/libbacktrace.a
../libiberty/libiberty.a ../libdecnumber/libdecnumber.a -o gcov-dump
../../gcc-trunk/libbacktrace/elf.c: In function 'elf_add':
../../gcc-trunk/libbacktrace/mmapio.c:98:14: error: 'ehdr_view.len' may be used
uninitialized in this function [-Werror=maybe-uninitialized]
if (munmap (const_cast.v, view->len) < 0)
^
../../gcc-trunk/libbacktrace/elf.c:476:25: note: 'ehdr_view.len' was declared
here
struct backtrace_view ehdr_view;
^
../../gcc-trunk/libbacktrace/mmapio.c:98:14: error: 'ehdr_view.base' may be
used uninitialized in this function [-Werror=maybe-uninitialized]
if (munmap (const_cast.v, view->len) < 0)
^
../../gcc-trunk/libbacktrace/elf.c:476:25: note: 'ehdr_view.base' was declared
here
struct backtrace_view ehdr_view;
^
../../gcc-trunk/libbacktrace/elf.c:516:10: error: 'ehdr_view.data' may be used
uninitialized in this function [-Werror=maybe-uninitialized]
memcpy (&ehdr, ehdr_view.data, sizeof ehdr);
^
../../gcc-trunk/libbacktrace/elf.c:476:25: note: 'ehdr_view.data' was declared
here
struct backtrace_view ehdr_view;
^
which is a false positive, because
ehdr_view's fields are correctly initialized via a call from elf_add() to
backtrace_get_view()
view->data = (char *) map + inpage;
view->base = map;
view->len = size;
if the mmap() earlier in the backtrace_get_view() didn't fail, view is
initialized and the backtrace_get_view() returns 1. if that mmap() fails, view
remains uninitialized and backtrace_get_view() returns 0.
elf_add()'s invocation checks the return value of backtrace_get_view(). in the
0 (failure) case, backtrace_release_view() is never invoked:
if (!backtrace_get_view (state, descriptor, 0, sizeof ehdr, error_callback,
data, &ehdr_view))
goto fail;
since backtrace_release_view() is never called in the case where the fields are
uninitialized, the warning is a false positive. while it occurs here with the
confluence of several optimizations, it looks like the same problem would
happen in a contrived single-file case.
attached are the temp files for the module the generated this false positive.
