URL:
<http://savannah.gnu.org/bugs/?51266>
Summary: "make -p" erroneously prints "+=" instead of ":="
Project: make
Submitted by: cmetcalf
Submitted on: Mon 19 Jun 2017 03:56:41 PM UTC
Severity: 3 - Normal
Item Group: Bug
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Component Version: 4.2
Operating System: POSIX-Based
Fixed Release: None
Triage Status: None
_______________________________________________________
Details:
When parsing a "make -p" output, an unexpected "+=" was seen in a context
where ":=" was expected (a target-specific variable being assigned with "=" to
a pattern target, e.g. "%.x: FOO = x").
The bug is extremely unstable; it required the exact build directory, and a
particular amount of data in the environment. Adding or removing unrelated
environment variables ("XXX_<blah>") would cause the bug to come and go.
Running "valgrind --track-origins=yes" made the bug jump out:
Conditional jump or move depends on uninitialised value(s)
at 0x42265D: print_variable (variable.c:1664)
by 0x4243F0: print_variable_data_base (variable.c:1746)
by 0x415CC5: print_data_base (main.c:3367)
by 0x416809: die (main.c:3443)
by 0x407664: main (main.c:2581)
Uninitialised value was created by a heap allocation
at 0x4C27BE3: malloc (vg_replace_malloc.c:299)
by 0x417698: xmalloc (misc.c:221)
by 0x4228E1: create_pattern_var (variable.c:54)
by 0x41D047: record_target_var (read.c:1860)
by 0x41D047: eval (read.c:1178)
by 0x41D8F3: eval_makefile (read.c:437)
by 0x41CB58: eval (read.c:904)
by 0x41DE76: eval_buffer (read.c:480)
by 0x40E925: func_eval (function.c:1403)
by 0x410E18: handle_function (function.c:2527)
by 0x40B17E: variable_expand_string (expand.c:258)
by 0x40BC12: allocated_variable_expand_for_file (expand.c:564)
by 0x40EF0C: func_foreach (function.c:888)
Indeed, it does not appear that the variable structure allocated in
create_pattern_var() is fully initialized. As a big hammer fix, I added a
memset() for the embedded "struct variable" to set it to zero; with this
change, the valgrind warning is fixed, and the flaky bug disappears (although
it's unstable enough that that doesn't by itself prove anything). However,
the valgrind warning points right to the code that chooses between ":=" and
"+=" when printing the variable, so it seems like a strong hypothesis.
diff --git a/variable.c b/variable.c
index 364774f05064..3f962b160019 100644
--- a/variable.c
+++ b/variable.c
@@ -88,6 +88,7 @@ create_pattern_var (const char *target, const char *suffix)
p->target = target;
p->len = len;
p->suffix = suffix + 1;
+ memset(&p->variable, 0, sizeof(p->variable));
if (len < 256)
last_pattern_vars[len] = p;
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