## Motivation
Since we don't need the metadata sections at runtime, we can somehow
offload them from memory at runtime. Initially, I explored [debug info
correlation](https://discourse.llvm.org/t/instrprofiling-lightweight-instrumentation/59113),
which is used for PGO with value profiling disabled. However, it
currently only works with DWARF and it's be hard to add such artificial
debug info for every function in to CodeView which is used on Windows.
So, offloading profile metadata sections at runtime seems to be a
platform independent option.
## Design
The idea is to use new section names for profile name and data sections
and mark them as metadata sections. Under this mode, the new sections
are non-SHF_ALLOC in ELF. So, they are not loaded into memory at runtime
and can be stripped away as a post-linking step. After the process
exits, the generated raw profiles will contains only headers + counters.
llvm-profdata can be used correlate raw profiles with the unstripped
binary to generate indexed profile.
## Data
For chromium base_unittests with code coverage on linux, the binary size
overhead due to instrumentation reduced from 64M to 38.8M (39.4%) and
the raw profile files size reduce from 128M to 68M (46.9%)
```
$ bloaty out/cov/base_unittests.stripped -- out/no-cov/base_unittests.stripped
FILE SIZE VM SIZE
-------------- --------------
+121% +30.4Mi +121% +30.4Mi .text
[NEW] +14.6Mi [NEW] +14.6Mi __llvm_prf_data
[NEW] +10.6Mi [NEW] +10.6Mi __llvm_prf_names
[NEW] +5.86Mi [NEW] +5.86Mi __llvm_prf_cnts
+95% +1.75Mi +95% +1.75Mi .eh_frame
+108% +400Ki +108% +400Ki .eh_frame_hdr
+9.5% +211Ki +9.5% +211Ki .rela.dyn
+9.2% +95.0Ki +9.2% +95.0Ki .data.rel.ro
+5.0% +87.3Ki +5.0% +87.3Ki .rodata
[ = ] 0 +13% +47.0Ki .bss
+40% +1.78Ki +40% +1.78Ki .got
+12% +1.49Ki +12% +1.49Ki .gcc_except_table
[ = ] 0 +65% +1.23Ki .relro_padding
+62% +1.20Ki [ = ] 0 [Unmapped]
+13% +448 +19% +448 .init_array
+8.8% +192 [ = ] 0 [ELF Section Headers]
+0.0% +136 +0.0% +80 [7 Others]
+0.1% +96 +0.1% +96 .dynsym
+1.2% +96 +1.2% +96 .rela.plt
+1.5% +80 +1.2% +64 .plt
[ = ] 0 -99.2% -3.68Ki [LOAD #5 [RW]]
+195% +64.0Mi +194% +64.0Mi TOTAL
$ bloaty out/cov-cor/base_unittests.stripped -- out/no-cov/base_unittests.stripped
FILE SIZE VM SIZE
-------------- --------------
+121% +30.4Mi +121% +30.4Mi .text
[NEW] +5.86Mi [NEW] +5.86Mi __llvm_prf_cnts
+95% +1.75Mi +95% +1.75Mi .eh_frame
+108% +400Ki +108% +400Ki .eh_frame_hdr
+9.5% +211Ki +9.5% +211Ki .rela.dyn
+9.2% +95.0Ki +9.2% +95.0Ki .data.rel.ro
+5.0% +87.3Ki +5.0% +87.3Ki .rodata
[ = ] 0 +13% +47.0Ki .bss
+40% +1.78Ki +40% +1.78Ki .got
+12% +1.49Ki +12% +1.49Ki .gcc_except_table
+13% +448 +19% +448 .init_array
+0.1% +96 +0.1% +96 .dynsym
+1.2% +96 +1.2% +96 .rela.plt
+1.2% +64 +1.2% +64 .plt
+2.9% +64 [ = ] 0 [ELF Section Headers]
+0.0% +40 +0.0% +40 .data
+1.2% +32 +1.2% +32 .got.plt
+0.0% +24 +0.0% +8 [5 Others]
[ = ] 0 -22.9% -872 [LOAD #5 [RW]]
-74.5% -1.44Ki [ = ] 0 [Unmapped]
[ = ] 0 -76.5% -1.45Ki .relro_padding
+118% +38.8Mi +117% +38.8Mi TOTAL
```
A few things to note:
1. llvm-profdata doesn't support filter raw profiles by binary id yet,
so when a raw profile doesn't belongs to the binary being digested by
llvm-profdata, merging will fail. Once this is implemented,
llvm-profdata should be able to only merge raw profiles with the same
binary id as the binary and discard the rest (with mismatched/missing
binary id). The workflow I have in mind is to have scripts invoke
llvm-profdata to get all binary ids for all raw profiles, and
selectively choose the raw pnrofiles with matching binary id and the
binary to llvm-profdata for merging.
2. Note: In COFF, currently they are still loaded into memory but not
used. I didn't do it in this patch because I noticed that `.lcovmap` and
`.lcovfunc` are loaded into memory. A separate patch will address it.
3. This should works with PGO when value profiling is disabled as debug
info correlation currently doing, though I haven't tested this yet.
When LLVM_PROFILE_FILE is set incorrectly (e.g. multiple %c) and it
falls back to use `default.profraw` name, but continuous mode is still
set. This might cause signal bus in the following scenario.
LLVM_PROFILE_FILE is set incorrectly (with "%c%c") for process A and B.
Suppose A starts first and falls back to use `default.profraw` and
mmaped its file content to memory. Later B starts and also falls back to
use `default.profraw`, but it will truncate the file because online
merging is disable when reseting to `default.profraw`. When A tries to
update counter via mmaped memory, signal bus will occur.
This fixes it by disabling continuous mode when reset to
default.profraw.
Part 1 of 3. This includes the LLVM back-end processing and profile
reading/writing components. compiler-rt changes are included.
Differential Revision: https://reviews.llvm.org/D138846
Functions with these attributes will be automatically called before
main() or after main() exits gracefully. In glibc environments, the
constructor function is passed the same arguments as main(), so that
signature is allowed. In all other environments, we require the function
to accept no arguments and either return `void` or `int`. The functions
must use the C calling convention. In C++ language modes, the functions
cannot be a nonstatic member function, or a consteval function.
Additionally, these reuse the same priority logic as the init_priority
attribute which explicitly reserved priorty values <= 100 or > 65535. So
we now diagnose use of reserved priorities the same as we do for the
init_priority attribute, but we downgrade the error to be a warning
which defaults to an error to ease use for implementers like compiler-rt
or libc.
This relands a633a3761fcbd0799426cbf5fbd7794961080e43 with fixes.
In multi threaded application, it is possible for one thread to
terminate the program while another is flushing profile information. We
setup a signal mask to delay SIGKILL so that we can safely flush the
profile.
This patch setups the mask earlier: it reduces the window during which a
SIGKILL can end the computation prematurely.
This fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1850940, where a
profiled firefox was encountering several:
LLVM Profile Error: Failed to write file "default_*.profraw": Broken
pipe
Co-authored-by: serge-sans-paille <sguelton@mozilla.com>
This seems to cause Clang to crash, see comments on the code review. Reverting
until the problem can be investigated.
> Part 1 of 3. This includes the LLVM back-end processing and profile
> reading/writing components. compiler-rt changes are included.
>
> Differential Revision: https://reviews.llvm.org/D138846
This reverts commit a50486fd736ab2fe03fcacaf8b98876db77217a7.
Part 1 of 3. This includes the LLVM back-end processing and profile
reading/writing components. compiler-rt changes are included.
Differential Revision: https://reviews.llvm.org/D138846
When using debug info correlation, value profiling needs to be switched off.
So, we are only merging counter sections. In that case the existance of data
section is just used to provide an extra check in case of corrupted profile.
This patch performs counter merging by iterating the counter section by counter
size and add them together.
Reviewed By: ellis, MaskRay
Differential Revision: https://reviews.llvm.org/D157632
Original patch: D157632.
Fixed the issue when data is 0 by relaxing the condition.
Reviewed By: ellis
Differential Revision: https://reviews.llvm.org/D159000
This reverts commit cf2cf195d5fb0a07c122c5c274bd6deb0790e015.
This breaks merging profiles when nothing is instrumented, see comments in https://reviews.llvm.org/D157632.
This also reverts follow-up commit bfc965c54fdbfe33a0785b45903b53fc11165f13.
When using debug info correlation, value profiling needs to be switched off.
So, we are only merging counter sections. In that case the existance of data
section is just used to provide an extra check in case of corrupted profile.
This patch performs counter merging by iterating the counter section by counter
size and add them together.
Reviewed By: ellis, MaskRay
Differential Revision: https://reviews.llvm.org/D157632
Temporal profiles do not support profile merging at runtime. The reason
is that each function can only store one timestamp and the
`llmv-profdata` tool is responsible for sampling traces during the merge
command. Report an error in `__llvm_profile_merge_from_buffer()` if
merging a temporal profile.
The added test also checks that lightweight profiles throw an error,
although this may be fixed in https://reviews.llvm.org/D157632
Reviewed By: MaskRay, zequanwu
Differential Revision: https://reviews.llvm.org/D157664
In `initializeProfileForContinuousMode`, we have already locked the profile file when merging is enabled, so there's no need to lock the same file second time in `openFileForMerging`.
On Linux/Darwin, the locking the same file twice doesn't cause any problem. But on Windows, it causes the problem to hang forever.
With this minor fix, continuous mode seems working with online merging on Windows.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D154748
I recently discovered that `.profraw` headers are expected to be 8 byte
aligned.
643ba926c1/llvm/lib/ProfileData/InstrProfReader.cpp (L503-L506)
When function entry coverage mode is used, function counters are single
bytes, so it is likely that the size of the counters section is not 8
byte aligned. We can add padding after the counters section to guarantee
this.
Reviewed By: kyulee, gulfem
Differential Revision: https://reviews.llvm.org/D152479
As described in [0], this extends IRPGO to support //Temporal Profiling//.
When `-pgo-temporal-instrumentation` is used we add the `llvm.instrprof.timestamp()` intrinsic to the entry of functions which in turn gets lowered to a call to the compiler-rt function `INSTR_PROF_PROFILE_SET_TIMESTAMP()`. A new field in the `llvm_prf_cnts` section stores each function's timestamp. Then in `llvm-profdata merge` we convert these function timestamps into a //trace// and add it to the indexed profile.
Since these traces could significantly increase the profile size, we've added `-max-temporal-profile-trace-length` and `-temporal-profile-trace-reservoir-size` to limit the length of a trace and the number of traces in a profile, respectively.
In a future diff we plan to use these traces to construct an optimized function order to reduce the number of page faults during startup.
Special thanks to Julian Mestre for helping with reservoir sampling.
[0] https://discourse.llvm.org/t/rfc-temporal-profiling-extension-for-irpgo/68068
Reviewed By: snehasish
Differential Revision: https://reviews.llvm.org/D147287
On AIX, the build-id can be embedded in a binary using the -mxcoff-build-id
compiler option. When present, the build id is stored as an ascii string at the
beginning of the string table in the loader section of the XCOFF file.
Reviewed By: stephenpeckham, daltenty
Differential Revision: https://reviews.llvm.org/D146976
This was reverted because it was breaking when targeting Darwin which
tried to export these symbols which are now hidden. It should be safe
to just stop attempting to export these symbols in the clang driver,
though Apple folks will need to change their TAPI allow list described
in the commit where these symbols were originally exported
f538018562
Then reverted again because it broke tests on MacOS, they should be
fixed now.
Bug: https://github.com/llvm/llvm-project/issues/58265
Differential Revision: https://reviews.llvm.org/D135340
This reverts commit 04877284b4592e9286cab43467662c1b4ff81861.
Looks like this is still breaking the test
Profile-x86_64 :: instrprof-darwin-dead-strip.c
(see comment on https://reviews.llvm.org/D135340).
This was reverted because it was breaking when targeting Darwin which
tried to export these symbols which are now hidden. It should be safe
to just stop attempting to export these symbols in the clang driver,
though Apple folks will need to change their TAPI allow list described
in the commit where these symbols were originally exported
f538018562
Bug: https://github.com/llvm/llvm-project/issues/58265
Differential Revision: https://reviews.llvm.org/D135340
1) Use a static array of pointer to retain the dummy vars.
2) Associate liveness of the array with that of the runtime hook variable
__llvm_profile_runtime.
3) Perform the runtime initialization through the runtime hook variable.
4) Preserve the runtime hook variable using the -u linker flag.
Reviewed By: hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D136192
When we use selective instrumentation and instrument a file
that is not in the selected files list provided via -fprofile-list,
we generate an empty raw profile. This leads to empty_raw_profile
error when we try to read that profile. This patch fixes the issue by
generating a raw profile that contains only a profile header when
there are no counters and profile data.
A small reproducer for the above issue:
echo "src:other.cc" > code.list
clang++ -O2 -fprofile-instr-generate -fcoverage-mapping
-fprofile-list=code.list code.cc -o code
./code
llvm-profdata show default.profraw
Differential Revision: https://reviews.llvm.org/D132094
that can lead to security vulnerabilities
Also, fix a few places that were causing -Wshadow and
-Wformat-nonliteral warnings to be emitted.
This reapplies the patch that was reverted in caaafe4ae250 because it
broke Fuchsia builders.
I reverted the changes I made to InstrProfData.inc and instead renamed
the variables in InstrProfilingWriter.c. Also fixed a bug in function
add_security_warnings that was causing it to pass -Wformat-nonliteral
when the compiler doesn't support it.
that can lead to security vulnerabilities
Also, fix a few places that were causing -Wshadow and
-Wformat-nonliteral warnings to be emitted.
This reapplies the patch that was reverted in 0d66dc57e8c7 because it
broke a few bots.
I made changes so that cmake checks whether some of the flags are
supported by the compiler that is used before adding them to the list.
Also, I moved function add_security_warnings to CompilerRTUtils.cmake so
that it is defined before it's used.
Differential Revision: https://reviews.llvm.org/D131714
that can lead to security vulnerabilities
Also, fix a few places that were causing -Wshadow and
-Wformat-nonliteral warnings to be emitted.
Differential Revision: https://reviews.llvm.org/D131714
This patch was pushed for calixte@mozilla.com
- this function (Windows only) is called when gcda are dumped on disk;
- according to its documentation, it's only useful in case of hard failures, this is highly improbable;
- it drastically decreases the time in the tests and consequently it avoids timeouts when we use slow disks.
Differential Revision: https://reviews.llvm.org/D129128
