neovim / neovim / 24628
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Jobs 1
Files 678
Run time 27s
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travis-ci

justinmk 
server.c: Fix bug in release mode (#7594)

When compiling with CMAKE_BUILD_TYPE=RelWithDebInfo, several
-Wmaybe-uninitialized warnings are printed. These were thought to
be false positives (#5061); there are no control paths that lead
to an uninitialized value. However, when gcc is run in -O2 mode,
it makes a mistake while generating the necessary logic.

Specifically, for the code:
...
  int = 0; // Index of the server whose address equals addr.
  for (; i < watchers.ga_len; i++) {
    watcher = ((SocketWatcher **)watchers.ga_data)[i];
    // <snip>
  }
  if (i >= watchers.ga_len) {
    ELOG("Not listening on %s", addr);
    return;
  }
...

Gcc generates:
...
<+98>:  cmp  %ebx, %ebp
<+100>: jg   0x530f13   <server_stop+55>
<+102>: cmp  %ebp, ebx
<+104>: jl   0x530f7e   <server_stop+162>
...

Normally, the if statement should catch the only control path
where watcher is not assigned: watchers.ga_len <= 0. When
compiled, the assembly lines 98 and 100 correspond to checking if
i < watchers.ga_len, and the lines 102 and 104 correspond to
checking if i >= watchers.ga_len. The assembly seems to compare
ebp (which is watchers.ga_len) with ebx (which is i), and jump
if greater; then do the same comparison and jump if less. This is
where gcc makes a mistake: it flips the order of the cmp
instruction. This means that the REAL behavior is first check if
i < watchers.ga_len and then check if i < watchers.ga_len. Which
means the code inside the if statement is NEVER executed; no
combination of i and watchers.ga_len will ever trigger ELOG().

So not only is this a use of an uninitialized value if
watchers.ga_len == 0 (or technically, if it's less than zero too),
it also clobbers any error detection if the for loop reaches the
last entry (which would normally cause i == watchers.ga_len too).

This commit fixes this issue by adding a bool to keep track of
whether a watcher was found during the loop. This makes gcc
gene... (continued)

87752 of 113450 relevant lines covered (77.35%)

181546.45 hits per line

Uncovered Existing Lines

Lines Coverage ∆ File
1
81.36
 -0.31% src/nvim/os/signal.c
2
94.79
 0.11% src/nvim/msgpack_rpc/server.c
3
85.48
 -0.33% src/nvim/tui/tui.c
4
83.43
 -0.3% src/nvim/undo.c
Jobs
ID Job ID Ran Files Coverage
7 24628.7 (GCOV=gcov-5 CMAKE_FLAGS="$CMAKE_FLAGS -DUSE_GCOV=ON") 678
77.35
 Travis Job 24628.7
Source Files on build 24628
Coverage ∆ File Lines Relevant Covered Missed Hits/Line