- `-Wmissing-prototypes` and `-Wmissing-variable-declarations` are
helpful for finding dead code and/or things that should be `static`
but aren't marked as such.
- `-Wunused-macros` is of similar utility, but for identifying dead macros.
- `-Wunreachable-code` and `-Wunreachable-code-aggressive` do exactly
what they say: flag unreachable code.
`read(2)` and `write(2)` may read or write fewer bytes than were
requested. In order to robustly ensure that all of the requested bytes
are read/written, these edge-cases must be handled.
There are several benefits to this:
1. It's cleaner and more reliable to use the builtin to
inform the compiler of assumptions instead of hoping that the
optimizer understands your intentions.
2. `clang` will warn you if any of your assumptions would produce
side-effects (which the compiler will discard). [This blog post](https://fastcompression.blogspot.com/2019/01/compiler-checked-contracts.html)
by Yann Collet highlights that a hazard of using the
`unreachable()`-based method of signaling assumptions is that it
can sometimes result in additional instructions being generated (see
[this Godbolt link](https://godbolt.org/z/lKNMs3) from the blog post
for an example).
As reported in #2449, under certain circumstances it's possible to get
stuck in an infinite loop attempting to purge from the HPA. We now
handle this by validating the HPA settings at the end of
configuration parsing and either normalizing them or aborting depending on
if `abort_conf` is set.
An arena's bins should normally be accessed via the `arena_get_bin`
function, which properly takes into account bin-shards. To ensure that
we don't accidentally commit code which incorrectly accesses the bins
directly, we mark the field with `__attribute__((deprecated))` with an
appropriate warning message, and suppress the warning in the few places
where directly accessing the bins is allowed.
In an attempt to make all headers self-contained, I inadvertently added
`#include`s which refer to intermediate, generated headers that aren't
included in the final install. Closes#2489.
Following from PR #2481, we replace all integer-to-pointer casts [which
hide pointer provenance information (and thus inhibit
optimizations)](https://clang.llvm.org/extra/clang-tidy/checks/performance/no-int-to-ptr.html)
with equivalent operations that preserve this information. I have
enabled the corresponding clang-tidy check in our static analysis CI so
that we do not get bitten by this again in the future.
[N2699 - Sized Memory Deallocation](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2699.htm)
introduced two new functions which were incorporated into the C23
standard, `free_sized` and `free_aligned_sized`. Both already have
analogues in Jemalloc, all we are doing here is adding the appropriate
wrappers.
Header files are now self-contained, which makes the relationships
between the files clearer, and crucially allows LSP tools like `clangd`
to function correctly in all of our header files. I have verified that
the headers are self-contained (aside from the various Windows shims) by
compiling them as if they were C files – in a follow-up commit I plan to
add this to CI to ensure we don't regress on this front.
This is a prerequisite to achieving self-contained headers. Previously,
the various tsd implementation headers (`tsd_generic.h`,
`tsd_tls.h`, `tsd_malloc_thread_cleanup.h`, and `tsd_win.h`) relied
implicitly on being included in `tsd.h` after a variety of dependencies
had been defined above them. This commit instead makes these
dependencies explicit by splitting them out into a separate file,
`tsd_internals.h`, which each of the tsd implementation headers includes
directly.
At least for LLVM, [casting from an integer to a pointer hides provenance information](https://clang.llvm.org/extra/clang-tidy/checks/performance/no-int-to-ptr.html)
and inhibits optimizations. Here's a [Godbolt link](https://godbolt.org/z/5bYPcKoWT)
showing how this change removes a couple unnecessary branches in
`phn_merge_siblings`, which is a very hot function. Canary profiles show
only minor improvements (since most of the cost of this function is in
cache misses), but there's no reason we shouldn't take it.
For the sake of consistency, function definitions and their
corresponding declarations should use the same names for parameters.
I've enabled this check in static analysis to prevent this issue from
occurring again in the future.
For better or worse, Jemalloc has a significant number of global
variables. Making all eligible global variables `static` and/or `const`
at least makes it slightly easier to reason about them, as these
qualifications communicate to the programmer restrictions on their use
without having to `grep` the whole codebase.
Previously, small allocations which were sampled as part of heap
profiling were rounded up to `SC_LARGE_MINCLASS`. This additional memory
usage becomes problematic when the page size is increased, as noted in #2358.
Small allocations are now rounded up to the nearest multiple of `PAGE`
instead, reducing the memory overhead by a factor of 4 in the most
extreme cases.
Additionally, added a GitHub Action to ensure no more trailing
whitespace will creep in again in the future.
I'm excluding Markdown files from this check, since trailing whitespace
is significant there, and also excluding `build-aux/install-sh` because
there is significant trailing whitespace on the line that sets
`defaultIFS`.
Fix or suppress the remaining warnings generated by static analysis.
This is a necessary step before we can incorporate static analysis into
CI. Where possible, I've preferred to modify the code itself instead of
just disabling the warning with a magic comment, so that if we decide to
use different static analysis tools in the future we will be covered
against them raising similar warnings.
In #2433, I inadvertently introduced a regression which causes the use of
uninitialized data. Namely, the control path I added for the safety
check in `arena_prof_info_get` neglected to set `prof_info->alloc_tctx`
when the check fails, resulting in `prof_info.alloc_tctx` being
uninitialized [when it is read at the end of
`prof_free`](90176f8a87/include/jemalloc/internal/prof_inlines.h (L272)).
Static analysis flagged this. It's possible to segfault in the
`*_tree_remove` function generated by `rb_gen`, as `nodep` may
still be `NULL` after the initial for loop. I can confirm from reviewing
the fleetwide coredump data that this was in fact being hit in
production, primarily through `tctx_tree_remove`, and much more rarely
through `gctx_tree_remove`.
This is in preparation for upcoming changes I plan to make to this
logic. Extracting it into a common function will make this easier and
less error-prone, and cleans up the existing code regardless.
None of these are harmful, and they are almost certainly optimized
away by the compiler. The motivation for fixing them anyway is that
we'd like to enable static analysis as part of CI, and the first step
towards that is resolving the warnings it produces at present.
The codebase is already very disciplined in making any function which
can be `static`, but there are a few that appear to have slipped through
the cracks.
`edata_cmp_summary_comp` is one of the very hottest functions, taking up
3% of all time spent inside Jemalloc. I noticed that all existing
callsites rely only on the sign of the value returned by this function,
so I came up with this equivalent branchless implementation which
preserves this property. After empirical measurement, I have found that
this implementation is 30% faster, therefore representing a 1% speed-up
to the allocator as a whole.
At @interwq's suggestion, I've applied the same optimization to
`edata_esnead_comp` in case this function becomes hotter in the future.
Decay should not be triggered during reentrant calls (may cause lock order
reversal / deadlocks). Added a delay_trigger flag to the tickers to bypass
decay when rentrancy_level is not zero.
This lowered the sizeof(prof_tdata_t) from 200 to 192 which is a round size
class. Afterwards the tdata_t size remain unchanged with the last commit, which
effectively inlined the storage of thread names for free.
The previous approach managed the thread name in a separate buffer, which causes
races because the thread name update (triggered by new samples) can happen at
the same time as prof dumping (which reads the thread names) -- these two
operations are under separate locks to avoid blocking each other. Implemented
the thread name storage as part of the tdata struct, which resolves the lifetime
issue and also avoids internal alloc / dalloc during prof_sample.
Also fixes what looks like an off by one error in the lazy aux list
merge part of the code that previously never touched the last node in
the aux list.
It turns out that the previous commit did not suffice since the
JEMALLOC_SYS_NOTHROW definition also causes the same exception specification
errors as JEMALLOC_USE_CXX_THROW did:
```
x86_64-pc-linux-musl-cc -std=gnu11 -Werror=unknown-warning-option -Wall -Wextra -Wshorten-64-to-32 -Wsign-compare -Wundef -Wno-format-zero-length -Wpointer-
arith -Wno-missing-braces -Wno-missing-field-initializers -pipe -g3 -fvisibility=hidden -Wimplicit-fallthrough -O3 -funroll-loops -march=native -O2 -pipe -c -march=native -O2 -pipe -D_GNU_SOURCE -D_REENTRANT -Iinclude -Iinclude -o src/background_thread.o src/background_thread.c
In file included from src/jemalloc_cpp.cpp:9:
In file included from include/jemalloc/internal/jemalloc_preamble.h:27:
include/jemalloc/internal/../jemalloc.h:254:32: error: exception specification in declaration does not match previous declaration
void JEMALLOC_SYS_NOTHROW *je_malloc(size_t size)
^
include/jemalloc/internal/../jemalloc.h:75:21: note: expanded from macro 'je_malloc'
^
/usr/x86_64-pc-linux-musl/include/stdlib.h:40:7: note: previous declaration is here
void *malloc (size_t);
^
```
On systems using the musl C library we have to omit the exception specification
on malloc function family like it's done for MacOS, FreeBSD and OpenBSD.
The added hooks hooks.prof_sample and hooks.prof_sample_free are intended to
allow advanced users to track additional information, to enable new ways of
profiling on top of the jemalloc heap profile and sample features.
The sample hook is invoked after the allocation and backtracing, and forwards
the both the allocation and backtrace to the user hook; the sample_free hook
happens before the actual deallocation, and forwards only the ptr and usz to the
hook.
