As was first reported by Ilya in issue #1513, compiling with gcc-12
adds warnings about size 0 around each BUG_ON() call due to the
ABORT_NOW() macro that tries to dereference pointer value 1.
The problem is known, seems to be complex inside gcc and could only
be worked around for now by adjusting a pointer limit so that the
warning still catches NULL derefs in the first page but not other
values commonly used in kernels and boot loaders:
https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=91f7d7e1b
It's described in more details here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104657https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103768
And some projects had to work around it using various approaches,
some of which are described in the bugs reports above, plus another
one here:
https://mail.coreboot.org/hyperkitty/list/seabios@seabios.org/thread/HLK3BHP2T3FN6FZ46BIPIK3VD5FOU74Z/
In haproxy we can hide it by hiding the pointer in a DISGUISE() macro,
but this forces the pointer to be loaded into a register, so that
register is lost precisely where we want to get the maximum of them.
In our case we purposely use a low-value non-null pointer because:
- it's mandatory that this value fits within an unmapped page and
only the lowest one has this property
- we really want to avoid register loads for the address, as these
will be lost and will complicate the bug analysis, and they tend
to be used for large addresses (i.e. instruction length limit).
- the compiler may decide to optimize away the null deref when it
sees it (seen in the past already)
As such, the current workaround merged in gcc-12 is not effective for
us.
Another approach consists in using pragmas to silently disable
-Warray-bounds and -Wnull-dereference only for this part. The problem
is that pragmas cannot be placed into macros.
The resulting solution consists in defining a forced-inlined function
only to trigger the crash, and surround the dereference with pragmas,
themselves conditionned to gcc >= 5 since older versions don't
understand them (but they don't complain on the dereference at least).
This way the code remains the same even at -O0, without the stack
pointer being modified nor any address register being modified on
common archs (x86 at least). A variation could have been to rely on
__builtin_trap() but it's not everywhere and it behaves differently
on different platforms (undefined opcode or a nasty abort()) while
the segv remains uniform and effective.
This may need to be backported to older releases once users start to
complain about gcc-12 breakage.
While weak symbols were finally fixed with commit fb1b6f5bc ("BUILD:
compiler: use a more portable set of asm(".weak") statements"), it
was an error to think that initcall symbols were also weak. They must
not be and they're only global. The reason is that any externally
linked code loaded as a .so would drop its weak symbols when being
loaded, hence its initcalls that may contain various function
registration calls.
The ambiguity came from the fact that we initially reused the initcall's
HA_GLOBL macro for OSX then generalized it, then turned it to a choice
between .globl and .weak based on the OS, while in fact we needed a
macro to define weak symbols.
Let's rename the macro to HA_WEAK() to make it clear it's only for weak
symbols, and redefine HA_GLOBL() that initcall needs.
This will need to be backported wherever the commit above is backported
(at least 2.5 for now).
The two recent patches b12966af1 ("BUILD: debug: mark the
__start_mem_stats/__stop_mem_stats symbols as weak") and 2a06e248f
("BUILD: initcall: mark the __start_i_* symbols as weak, not global")
aimed at fixing a build warning and resulted in a build breakage on
MacOS which doesn't have a ".weak" asm statement.
We've already had MacOS-specific asm() statements for section names, so
this patch continues on this trend by moving HA_GLOBL() to compiler.h
and using ".globl" on MacOS since apparently nobody complains there.
It is debatable whether to expose this only when !USE_OBSOLETE_LINKER
or all the time, but since these are just macroes it's no big deal to
let them be available when needed and let the caller decide on the
build conditions.
If any of the patches above is backported, this one will need to as
well.
Building with clang and DEBUG_MEM_STATS shows the following warnings:
warning: __start_mem_stats changed binding to STB_WEAK [-Wsource-mgr]
warning: __stop_mem_stats changed binding to STB_WEAK [-Wsource-mgr]
The reason is that the symbols are declared using ".globl" while they
are also referenced as __attribute__((weak)) elsewhere. It turns out
that a weak symbol is implicitly a global one and that the two classes
are exclusive, thus it may confuse the linker. Better fix this.
This may be backported where the patch applies.
Many inline functions involve some BUG_ON() calls and because of the
partial complexity of the functions, they're not inlined anymore (e.g.
co_data()). The reason is that the expression instantiates the message,
its size, sometimes a counter, then the atomic OR to taint the process,
and the back trace. That can be a lot for an inline function and most
of it is always the same.
This commit modifies this by delegating the common parts to a dedicated
function "complain()" that takes care of updating the counter if needed,
writing the message and measuring its length, and tainting the process.
This way the caller only has to check a condition, pass a pointer to the
preset message, and the info about the type (bug or warn) for the tainting,
then decide whether to dump or crash. Note that this part could also be
moved to the function but resulted in complain() always being at the top
of the stack, which didn't seem like an improvement.
Thanks to these changes, the BUG_ON() calls do not result in uninlining
functions anymore and the overall code size was reduced by 60 to 120 kB
depending on the build options.
The new macro was introduced with commit 86bcc5308 ("DEBUG: implement 4
levels of choices between warn and crash.") but some older compilers can
complain that we test the value when the macro is not defined despite
having already been checked in a previous #if directive. Let's just
repeat the test for the definition.
Two new BUG_ON variants, BUG_ON_HOT() and CHECK_IF_HOT() are introduced
to debug hot paths (such as low-level API functions). These ones must
not be enabled by default as they would significantly affect performance
but they may be enabled by setting DEBUG_STRICT to a value above 1. In
this case, DEBUG_STRICT_ACTION is mostly respected with a small change,
which is that the no_crash variant of BUG_ON() isn't turned to a regular
warning but to a one-time warning so as not to spam with warnings in a
hot path. It is for this reason that there is no WARN_ON_HOT().
We used to have DEBUG_STRICT_NOCRASH to disable crashes on BUG_ON().
Now we have other levels (WARN_ON(), CHECK_IF()) so we need something
finer-grained.
This patch introduces DEBUG_STRICT_ACTION which takes an integer value.
0 disables crashes and is the equivalent of DEBUG_STRICT_NOCRASH. 1 is
the default and only enables crashes on BUG_ON(). 2 also enables crashes
on WARN_ON(), and 3 also enables warnings on CHECK_IF(), and is suited
to developers and CI.
Now we'll explicitly mention if the test was a bug/warn/check, and
"FATAL" is only displayed when the process crashes. The non-crashing
BUG_ON() also suggests to report to developers.
The only reason for warning once is to check if a condition really
happens. Let's use a term that better translates the intent, that's
important when reading the code.
This one will maintain a static counter per call place and will only
emit the warning on the first call. It may be used to invite users to
report an unexpected event without spamming them with messages.
This is the same as BUG_ON() except that it never crashes and only emits
a warning and a backtrace, inviting users to report the problem. This will
be usable for non-fatal issues that should not happen and need to be fixed.
This way the BUG_ON() when using DEBUG_STRICT_NOCRASH is effectively an
equivalent of WARN_ON().
The purpose is to make the program die at this point, so let's help the
compiler optimise the code (especially in sensitive areas) by telling it
that ABORT_NOW() does not return. This reduces the overall code size by
~0.5%.
The BUG_ON() macro handling is complicated because it relies on a
conditional CRASH_NOW() macro whose definition depends on DEBUG_STRICT
and DEBUG_STRICT_NOCRASH. Let's rethink the whole thing differently,
and instead make the underlying _BUG_ON() macro take a crash argument
to decide whether to crash or not, as well as a prefix and a suffix for
the message, that will allow to distinguish between variants. Now the
suffix is set to a message explaining we don't crash when needed.
This also allows to get rid of the CRASH_NOW() macro and to define
much simpler new macros.
The functions needed to manipulate the "tainted" flags were located in
too high a level to be callable from the lower code layers. Let's move
them to bug.h.
ha_backtrace_to_stderr() must be declared in CRASH_NOW() macro whe HAProxy
is compiled with DEBUG_STRICT_NOCRASH. Otherwise an error is reported during
compilation:
include/haproxy/bug.h:58:26: error: implicit declaration of function ‘ha_backtrace_to_stderr’ [-Werror=implicit-function-declaration]
58 | #define CRASH_NOW() do { ha_backtrace_to_stderr(); } while (0)
This patch must be backported as far as 2.4.
"f(void)" is the correct and preferred form for a function taking no
argument, while some places use the older "f()". These were reported
by clang's -Wmissing-prototypes, for example:
src/cpuset.c:111:5: warning: no previous prototype for function 'ha_cpuset_size' [-Wmissing-prototypes]
int ha_cpuset_size()
include/haproxy/cpuset.h:42:5: note: this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function
int ha_cpuset_size();
^
void
This aggregate patch fixes this for the following functions:
ha_backtrace_to_stderr(), ha_cpuset_size(), ha_panic(), ha_random64(),
ha_thread_dump_all_to_trash(), get_exec_path(), check_config_validity(),
mworker_child_nb(), mworker_cli_proxy_(create|stop)(),
mworker_cleantasks(), mworker_cleanlisteners(), mworker_ext_launch_all(),
mworker_reload(), mworker_(env|proc_list)_to_(proc_list|env)(),
mworker_(un|)block_signals(), proxy_adjust_all_maxconn(),
proxy_destroy_all_defaults(), get_tainted(),
pool_total_(allocated|used)(), thread_isolate(_full|)(),
thread(_sync|)_release(), thread_harmless_till_end(),
thread_cpu_mask_forced(), dequeue_all_listeners(), next_timer_expiry(),
wake_expired_tasks(), process_runnable_tasks(), init_acl(),
init_buffer(), (de|)init_log_buffers(), (de|)init_pollers(),
fork_poller(), pool_destroy_all(), pool_evict_from_local_caches(),
pool_total_failures(), dump_pools_to_trash(), cfg_run_diagnostics(),
tv_init_(process|thread)_date(), __signal_process_queue(),
deinit_signals(), haproxy_unblock_signals()
This patch replaces roughly all occurrences of an HA_ATOMIC_ADD(&foo, 1)
or HA_ATOMIC_SUB(&foo, 1) with the equivalent HA_ATOMIC_INC(&foo) and
HA_ATOMIC_DEC(&foo) respectively. These are 507 changes over 45 files.
TCC happens to define __OPTIMIZE__ at -O2 but doesn't proceed with dead
code elimination, resulting in ha_free() to always reference the link
error symbol. Let's condition this test on __GCC__ which others like
Clang also define.
ha_free() uses code that attempts to set a non-existant variable to provoke
a link-time error, with the expectation that the compiler will not omit that
if the code is unreachable. However, clang will emit it when compiling with
no optimization, so only do that if __OPTIMIZE__ is defined.
This makes the code more readable and less prone to copy-paste errors.
In addition, it allows to place some __builtin_constant_p() predicates
to trigger a link-time error in case the compiler knows that the freed
area is constant. It will also produce compile-time error if trying to
free something that is not a regular pointer (e.g. a function).
The DEBUG_MEM_STATS macro now also defines an instance for ha_free()
so that all these calls can be checked.
178 occurrences were converted. The vast majority of them were handled
by the following Coccinelle script, some slightly refined to better deal
with "&*x" or with long lines:
@ rule @
expression E;
@@
- free(E);
- E = NULL;
+ ha_free(&E);
It was verified that the resulting code is the same, more or less a
handful of cases where the compiler optimized slightly differently
the temporary variable that holds the copy of the pointer.
A non-negligible amount of {free(str);str=NULL;str_len=0;} are still
present in the config part (mostly header names in proxies). These
ones should also be cleaned for the same reasons, and probably be
turned into ist strings.
The purpose is to enable the dumping of a backtrace on BUG_ON(). While
it's very useful to know that a condition was met, very often some
caller context is missing to figure how the condition could happen.
From now on, on systems featuring backtrace, a backtrace of the calling
thread will also be dumped to stderr in addition to the unexpected
condition. This will help users of DEBUG_STRICT as they'll most often
find this backtrace in their logs even if they can't find their core
file.
A new "debug dev bug" expert-mode CLI command was added to test the
feature.
The mem stats are pretty convenient to spot leaks, except that they count
free(NULL) as 1, and the code does actually have quite a number of free(foo)
guards where foo is NULL if the object was already freed. Let's just not
count these ones so that the stats remain consistent. Now it's possible
to compare the strdup()/malloc() and free() and verify they are consistent.
Now when building with -DDEBUG_MEM_STATS, some malloc/calloc/strdup/realloc
stats are kept per file+line number and may be displayed and even reset on
the CLI using "debug dev memstats". This allows to easily track potential
leakers or abnormal usages.
This one used to be stored into debug.h but the debug tools got larger
and require a lot of other includes, which can't use BUG_ON() anymore
because of this. It does not make sense and instead this macro should
be placed into the lower includes and given its omnipresence, the best
solution is to create a new bug.h with the few surrounding macros needed
to trigger bugs and place assertions anywhere.
Another benefit is that it won't be required to add include <debug.h>
anymore to use BUG_ON, it will automatically be covered by api.h. No
less than 32 occurrences were dropped.
The FSM_PRINTF macro was dropped since not used at all anymore (probably
since 1.6 or so).
