c++ - "Conditional jump or move depends on uninitialised value"，但堆栈跟踪中未列出分配函数。如何？

Question

这是一些 Valgrind 日志的一部分:

==1652== Conditional jump or move depends on uninitialised value(s)==1652==    at 0x868DBFC: Dfm_db::io::Layer_cell_writer::end_cell() (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_db_io_layer.C:224)==1652==    by 0x862C9FD: Dfm_db::Hdb_layer_writer::end_cell() (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/../Isrc/dfm/dfm_db_io_layer.h:916)==1652==    by 0x861197F: Dfm_db::Hdb_writer::save_layer_geometries(Dfm_db::Hdb_layer_writer&, Drc_Hierarchical_database&, unsigned long, Drc_Hierarchical_geometry_type, bool, bool, bool, bool, Dfm_produced_layer_type) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_db_hdb_io.C:2362)==1652==    by 0x8610755: Dfm_db::Hdb_writer::save_layer(Dfm_db::Database*, Drc_Hierarchical_database&, unsigned long, unsigned long, Dfm_db::Geometry_types, char const*, Dfm_db::Run_info&, Dfm_db::Layer_origin const&, char const*, bool, char const*, char const*, bool, Pdb_security*, bool, int, bool, bool, Dfm_db::must_be, Dfm_produced_layer_type) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_db_hdb_io.C:2102)==1652==    by 0x8595B1E: Dfm_db::Database::save_layer(char const*, unsigned long, bool) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_database.C:2490)==1652==    by 0x8594D39: Dfm_db::Database::save_layers(std::map, std::less, std::allocator > > >&) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_database.C:2317)==1652==    by 0x85937B8: Dfm_db::Database::save_revision(bool) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_database.C:2082)==1652==    by 0x4C6AE76: Cockpit_cli::save_revision(Dfm_db::must_be) (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/cockpit_db_rev_cli.C:520)==1652==    by 0x4C15153: cockpit_save_revision (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/cockpit_db_hier_rev_cmds.C:529)==1652==    by 0xD8BAC67: TclEvalObjvInternal (in /amy/ic_wg_server/CACHED_WG_SERVER/ic/comp/exports.v0-0_6-19-2015_engr-aoi/mgc_home/pkgs/icv_lib.aoi/lib64/libcalibre_utils.so)==1652==    by 0xD8E3255: TclExecuteByteCode (in /amy/ic_wg_server/CACHED_WG_SERVER/ic/comp/exports.v0-0_6-19-2015_engr-aoi/mgc_home/pkgs/icv_lib.aoi/lib64/libcalibre_utils.so)==1652==    by 0xD8E7280: TclCompEvalObj (in /amy/ic_wg_server/CACHED_WG_SERVER/ic/comp/exports.v0-0_6-19-2015_engr-aoi/mgc_home/pkgs/icv_lib.aoi/lib64/libcalibre_utils.so)==1652==  Uninitialised value was created by a stack allocation==1652==    at 0x859F6DC: Dfm_db::Database::get_pl_index_level() const (/home/lvardany/tmp_IWA/ic/lv/aoi-asserts-valg/dfm/Isrc/dfm_database.C:4325)

最后一行是 --track-origins 选项的结果，它准确显示了在哪个函数中创建了未初始化的值。这个输出对我来说唯一神奇的部分是最后一个函数没有出现在调用堆栈中。还为 20 提供了 --num-callers 选项。

我的问题是最后一个函数怎么可能没有出现在调用堆栈中？

Answer 1

很容易。一个例子:

#include <functional>
#include <iostream>

std::function<void()> callback;

void foo()
{
   int x;
   callback = [&]() { if (x > 5) std::cout << "hi"; };
}

int main()
{
   foo();
   callback();
}

这里，foo不会出现在调用callback的调用栈中。

你的想法太线性了。