[libc++][print] Adds FILE functions.

[Mordante]

Summary

Drive-by fix to make sure the __retarget_buffer works correctly whan
using a hint of 1. This was discovered in one of the new tests.

Drive-by fixes __retarget_buffer when initialized with size 1.

Implements parts of

• P2093R14 Formatted output
• P2539R4 Should the output of std::print to a terminal be synchronized with the underlying stream?

[Mordante]

libcxx/include/print

201

Yes it's indeed POSIX and provided by unistd. I followed the method of src/filesystem/operations.cpp where we include this when not on Windows. Other places use #if __has_include(<unistd.h>), so I switch to that method.

309

Good point!

libcxx/src/print.cpp

18

I checked, we use lower case everywhere.

libcxx/test/libcxx/input.output/iostream.format/print.fun/vprint_unicode_windows.pass.cpp

42

I prefer to keep it since this was needed for GCC. I still hope we can enable format/print with GCC in the near future.

[Mordante]

Addresses review comments.

[ldionne]

Nice, thanks! There's a lot of details in this patch, but it means that users would have a really hard time doing this right if they did it themselves!

libcxx/docs/Status/FormatPaper.csv

51

I think this should be 17.0, and this patch needs to be rebased.

libcxx/include/print

67

103–108

I don't think this hunk should be in this patch.

184

We could reorder like this instead, I think it would be easier to follow:

#ifdef _LIBCPP_HAS_NO_UNICODE
inline constexpr bool __use_unicode = false;
#elif defined(_MSVC_EXECUTION_CHARACTER_SET)
inline constexpr bool __use_unicode = _MSVC_EXECUTION_CHARACTER_SET == 65001;
#else
inline constexpr bool __use_unicode = true;
#endif

WDYT? This removes one layer.

186–187

207

Can you link to http://llvm.org/PR61563? Same thing below.

210

Let's use _LIBCPP_UNCATEGORIZED_ASSERT everywhere for now.

228

254

311

344–347

Suggestions:

1. Don't define this function when unicode has been disabled. It's less surprising to have a compilation error when using this function on a system where unicode has been disabled than to call it and get non-unicode output.
2. Don't define __vprint_unicode (above) when unicode is disabled.
3. Switch the if constexpr (__print::__use_unicode) above in println and print to #if <USE UNICODE>

libcxx/src/print.cpp

44

I think this comment is outdated.

46

I don't think this function is needed outside of Windows anymore, since you now use a macro for testing. This would also get rid of the diff in the ABI list.

55

__throw_system_error? This way you don't need ifndef _LIBCPP_HAS_NO_EXCEPTIONS.

libcxx/test/libcxx/input.output/iostream.format/print.fun/transcoding.pass.cpp

39–42 ↗

(On Diff #536525)

I don't think this should be specific to Glibc?

libcxx/test/libcxx/input.output/iostream.format/print.fun/vprint_unicode_posix.pass.cpp

45

49

Maybe we can use ranges::all_of here too?

libcxx/test/std/input.output/iostream.format/print.fun/print.file.pass.cpp

68

We're not using _POSIX_C_SOURCE anywhere in the code base right now, and it looks like at least macOS doesn't define it properly. I generally try to steer away from checking specific macros in the test suite if I can because it's easy to disable tests without intending it.

Instead, I would suggest moving this test to another .pass.cpp file and we can mark it as XFAIL or UNSUPPORTED on the relevant platforms.

71

libcxx/test/std/input.output/iostream.format/print.fun/print_tests.h

68

Can you add some unicode test cases here? It should just write the data as-is IIUC.

libcxx/utils/libcxx/test/header_information.py

42

Can you keep this list sorted?

[Mordante]

Addresses review comments.

[Mordante]

Thanks for the review!

libcxx/include/print

184

Yes this looks better.

207

I slightly changed the message to include the report, I prefer to keep it at this location instead of before the template. Some functions have useful comment which I don't want to clutter with this todo.

libcxx/test/libcxx/input.output/iostream.format/print.fun/transcoding.pass.cpp

39–42 ↗

(On Diff #536525)

Since this is not a part of this patch, I'll do the all_of change separately.

[Mordante]

CI fixes.

[Mordante]

Retrigger CI.

[Mordante]

Rebased and removed parent dependencies. Hopefully this lets the CI ruun.

[Mordante]

CI fixes.

[Mordante]

Fixes building on Windows.

[Mordante]

libcxx/src/print.cpp

52–53

This changes back to the original version. The function __throw_system_error is in the dylib but has no error code overload. I don't think we need to add an overload for one usage.

[ldionne]

libcxx/src/print.cpp

52–53

We could add an overload in another patch to address https://reviews.llvm.org/D154995#inline-1500381 at the same time.

[Mordante]

libcxx/src/print.cpp

52–53

As discussed I'll do that in a follow-up patch.

[hctim]

Edit: May have misattributed this due to changes in vprint files, but I'm bisecting now. There were ~4 other libcxx changes that I'm not 100% confident this is the culprit.

Hi folks,

Looks like this broke sanitizer buildbots, in https://lab.llvm.org/buildbot/#/builders/237/builds/3578:

llvm-libc++-shared.cfg.in :: std/input.output/iostream.format/print.fun/vprint_nonunicode.file.pass.cpp
llvm-libc++-shared.cfg.in :: std/input.output/iostream.format/print.fun/vprint_unicode.file.pass.cpp

(the other failure has since gone away)

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50
FAIL: llvm-libc++-shared.cfg.in :: std/input.output/iostream.format/print.fun/vprint_unicode.file.pass.cpp (5373 of 10181)
******************** TEST 'llvm-libc++-shared.cfg.in :: std/input.output/iostream.format/print.fun/vprint_unicode.file.pass.cpp' FAILED ********************
Script:
--
: 'COMPILED WITH';  /b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm_build0/bin/clang++ /b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/std/input.output/iostream.format/print.fun/vprint_unicode.file.pass.cpp -pthread --target=aarch64-unknown-linux-gnu -g -fno-omit-frame-pointer -fsanitize=memory -nostdinc++ -I /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/include/c++/v1 -I /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/include/c++/v1 -I /b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/support -std=c++26 -Werror -Wall -Wctad-maybe-unsupported -Wextra -Wshadow -Wundef -Wunused-template -Wno-unused-command-line-argument -Wno-attributes -Wno-pessimizing-move -Wno-noexcept-type -Wno-atomic-alignment -Wno-reserved-module-identifier -Wno-user-defined-literals -Wno-tautological-compare -Wsign-compare -Wunused-variable -Wunused-parameter -Wunreachable-code -Wno-unused-local-typedef -Wno-local-type-template-args -Wno-c++11-extensions -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D_LIBCPP_ENABLE_EXPERIMENTAL -Werror=thread-safety -Wuser-defined-warnings  -lc++experimental -nostdlib++ -L /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/lib -Wl,-rpath,/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/lib -lc++ -o /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir/t.tmp.exe
: 'EXECUTED AS';  "/usr/bin/python3.10" /b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/../utils/run.py --execdir /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir --  /b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir/t.tmp.exe
--
Exit Code: 250
Command Output (stdout):
--
$ ":" "COMPILED WITH"
note: command had no output on stdout or stderr
$ "/b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm_build0/bin/clang++" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/std/input.output/iostream.format/print.fun/vprint_unicode.file.pass.cpp" "-pthread" "--target=aarch64-unknown-linux-gnu" "-g" "-fno-omit-frame-pointer" "-fsanitize=memory" "-nostdinc++" "-I" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/include/c++/v1" "-I" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/include/c++/v1" "-I" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/support" "-std=c++26" "-Werror" "-Wall" "-Wctad-maybe-unsupported" "-Wextra" "-Wshadow" "-Wundef" "-Wunused-template" "-Wno-unused-command-line-argument" "-Wno-attributes" "-Wno-pessimizing-move" "-Wno-noexcept-type" "-Wno-atomic-alignment" "-Wno-reserved-module-identifier" "-Wno-user-defined-literals" "-Wno-tautological-compare" "-Wsign-compare" "-Wunused-variable" "-Wunused-parameter" "-Wunreachable-code" "-Wno-unused-local-typedef" "-Wno-local-type-template-args" "-Wno-c++11-extensions" "-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER" "-D_LIBCPP_ENABLE_EXPERIMENTAL" "-Werror=thread-safety" "-Wuser-defined-warnings" "-lc++experimental" "-nostdlib++" "-L" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/lib" "-Wl,-rpath,/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/lib" "-lc++" "-o" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir/t.tmp.exe"
note: command had no output on stdout or stderr
$ ":" "EXECUTED AS"
note: command had no output on stdout or stderr
$ "/usr/bin/python3.10" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/llvm-project/libcxx/test/../utils/run.py" "--execdir" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir" "--" "/b/sanitizer-aarch64-linux-bootstrap-msan/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_unicode.file.pass.cpp.dir/t.tmp.exe"
# command stderr:
libc++abi: terminating due to uncaught exception of type std::__1::format_error: Argument index out of bounds
error: command failed with exit status: 250

You can reproduce the exact bot with https://github.com/google/sanitizers/wiki/SanitizerBotReproduceBuild (buildbot_bootstrap_msan.sh is that particular bot), but I suspect a libcxxabi-libcxx bootstrap build should be sufficient to reproduce.

[Mordante]

In D150044#4514158, @hctim wrote:

Edit: May have misattributed this due to changes in vprint files, but I'm bisecting now. There were ~4 other libcxx changes that I'm not 100% confident this is the culprit.

This indeed looks like the culprit.

You can reproduce the exact bot with https://github.com/google/sanitizers/wiki/SanitizerBotReproduceBuild (buildbot_bootstrap_msan.sh is that particular bot), but I suspect a libcxxabi-libcxx bootstrap build should be sufficient to reproduce.

Unfortunately I can't reproduce it locally (Linux x86_64). I see https://lab.llvm.org/buildbot/#/builders/74 the x86_64 msan buildbot is happy but the aarch64. The exception in the logs is thrown in the test, but it seems it's not caught. Is it possible to see where the exception is thrown? Or can I get access to the buildbot to run some tests?

[hctim]

In D150044#4515133, @Mordante wrote:

Unfortunately I can't reproduce it locally (Linux x86_64). I see https://lab.llvm.org/buildbot/#/builders/74 the x86_64 msan buildbot is happy but the aarch64. The exception in the logs is thrown in the test, but it seems it's not caught. Is it possible to see where the exception is thrown? Or can I get access to the buildbot to run some tests?

Let me see if I can get you a stack trace (it might take me until ~tomorrow). Is it possible to revert/skip these tests on aarch64 in the meantime?

[Mordante]

In D150044#4515393, @hctim wrote:

In D150044#4515133, @Mordante wrote:

Unfortunately I can't reproduce it locally (Linux x86_64). I see https://lab.llvm.org/buildbot/#/builders/74 the x86_64 msan buildbot is happy but the aarch64. The exception in the logs is thrown in the test, but it seems it's not caught. Is it possible to see where the exception is thrown? Or can I get access to the buildbot to run some tests?

Let me see if I can get you a stack trace (it might take me until ~tomorrow). Is it possible to revert/skip these tests on aarch64 in the meantime?

Thanks! It's a bit tricky to find the proper flags to only disable it on aarch64 with msan. Instead I'll disable it for all msan builds.

[hctim]

In D150044#4515777, @Mordante wrote:

Thanks! It's a bit tricky to find the proper flags to only disable it on aarch64 with msan. Instead I'll disable it for all msan builds.

Unfortunately that doesn't quite do the trick, as we're also seeing the bug on the aarch64 asan and aarch64 hwasan bots as well :(.

[Mordante]

In D150044#4519110, @hctim wrote:

In D150044#4515777, @Mordante wrote:

Thanks! It's a bit tricky to find the proper flags to only disable it on aarch64 with msan. Instead I'll disable it for all msan builds.

Unfortunately that doesn't quite do the trick, as we're also seeing the bug on the aarch64 asan and aarch64 hwasan bots as well :(.

I indeed only turned of msan, doing it for asan and hwsan is trivial. Are the other sanitizers that fail?

[hctim]

In D150044#4519273, @Mordante wrote:

I indeed only turned of msan, doing it for asan and hwsan is trivial. Are the other sanitizers that fail?

The aarch64-ubsan build bot is fine, so it's just aarch64_{asan,msan,hwasan}. Still looking into getting you a stack trace or some other debugging info.

[Mordante]

In D150044#4519320, @hctim wrote:

In D150044#4519273, @Mordante wrote:

I indeed only turned of msan, doing it for asan and hwsan is trivial. Are the other sanitizers that fail?

The aarch64-ubsan build bot is fine, so it's just aarch64_{asan,msan,hwasan}. Still looking into getting you a stack trace or some other debugging info.

I've committed a fix for these two sanitizers too. Thanks for the info.

[hctim]

$ lldb /home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe
(lldb) target create "/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe"                                            Current executable set to '/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe' (aarch64).                            (lldb) r
Process 737940 launched: '/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe' (aarch64)
Process 737940 stopped and restarted: thread 1 received signal: SIGCHLD
libc++abi: terminating due to uncaught exception of type std::__1::format_error: Argument index out of bounds
Process 737940 stopped
* thread #1, name = 't.tmp.exe', stop reason = signal SIGABRT
    frame #0: 0x0000fffff7ac7eac libc.so.6`__GI_raise(sig=6) at raise.c:51:1
(lldb) bt
* thread #1, name = 't.tmp.exe', stop reason = signal SIGABRT
  * frame #0: 0x0000fffff7ac7eac libc.so.6`__GI_raise(sig=6) at raise.c:51:1
    frame #1: 0x0000fffff7ab4aa0 libc.so.6`__GI_abort at abort.c:79:7
    frame #2: 0x0000fffff7dd4948 libc++abi.so.1`abort_message at abort_message.cpp:78:5
    frame #3: 0x0000fffff7d8a1f0 libc++abi.so.1`::demangling_terminate_handler() at cxa_default_handlers.cpp:72:9
    frame #4: 0x0000fffff7dd3138 libc++abi.so.1`std::__terminate(void (*)()) at cxa_handlers.cpp:59:9
    frame #5: 0x0000fffff7dda23c libc++abi.so.1`__cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) at cxa_exception.cpp:152:5
    frame #6: 0x0000fffff7dda168 libc++abi.so.1`::__cxa_throw() at cxa_exception.cpp:283:5
    frame #7: 0x0000aaaaaabdbfac t.tmp.exe`std::__1::__throw_format_error[abi:v170000](__s="Argument index out of bounds") at format_error.h:41:3
    frame #8: 0x0000aaaaaabdf058 t.tmp.exe`auto char const* std::__1::__format::__handle_replacement_field[abi:v170000]<char const*, std::__1::basic_format_parse_context<char>, std::__1::basic_format_cont
ext<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(this=0x0000ffffffffe0c0, __arg=monostate @ 0x0000ffffffffdeaf)::'lambda'(char const*)::operator()<std::__1::monostate>
(char const*) const at format_functions.h:274:13
    frame #9: 0x0000aaaaaabdefe8 t.tmp.exe`decltype(std::declval<char const*>()(std::declval<std::__1::monostate&>())) std::__1::__invoke[abi:v170000]<char const* std::__1::__format::__handle_replacement_
field[abi:v170000]<char const*, std::__1::basic_format_parse_context<char>, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(char const*, ch
ar const*, std::__1::basic_format_parse_context<char>&, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>&)::'lambda'(char const*), std::__1::
monostate&>(__f=0x0000ffffffffe0c0, __args=0x0000ffffffffe0a0) at invoke.h:340:25
    frame #10: 0x0000aaaaaabde430 t.tmp.exe`std::__1::invoke_result<char const*, std::__1::monostate&>::type std::__1::invoke[abi:v170000]<char const* std::__1::__format::__handle_replacement_field[abi:v1
70000]<char const*, std::__1::basic_format_parse_context<char>, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(char const*, char const*, s
td::__1::basic_format_parse_context<char>&, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>&)::'lambda'(char const*), std::__1::monostate&>(
__f=0x0000ffffffffe0c0, __args=0x0000ffffffffe0a0) at invoke.h:30:12
    frame #11: 0x0000aaaaaabdcfa0 t.tmp.exe`decltype(auto) std::__1::__visit_format_arg[abi:v170000]<char const* std::__1::__format::__handle_replacement_field[abi:v170000]<char const*, std::__1::basic_fo
rmat_parse_context<char>, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(char const*, char const*, std::__1::basic_format_parse_context<ch
ar>&, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>&)::'lambda'(char const*), std::__1::basic_format_context<std::__1::back_insert_iterato
r<std::__1::__format::__output_buffer<char>>, char>>(__vis=0x0000ffffffffe0c0, __arg=basic_format_arg<std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char
> >, char> > @ 0x0000ffffffffe0a0) at format_arg.h:103:12
    frame #12: 0x0000aaaaaabdc404 t.tmp.exe`char const* std::__1::__format::__handle_replacement_field[abi:v170000]<char const*, std::__1::basic_format_parse_context<char>, std::__1::basic_format_context<
std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(__begin="}", __end="", __parse_ctx=0x0000ffffffffe408, __ctx=0x0000ffffffffe3c8) at format_functions.h:271:5
    frame #13: 0x0000aaaaaabd7ddc t.tmp.exe`std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>::iterator std::__1::__format::__vformat_to[abi:v
170000]<std::__1::basic_format_parse_context<char>, std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>(__parse_ctx=0x0000ffffffffe408, __ctx=0
x0000ffffffffe3c8) at format_functions.h:312:13
    frame #14: 0x0000aaaaaabd7738 t.tmp.exe`std::__1::back_insert_iterator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>> std::__1::__vformat_to[abi:v170000]<std::__1::back_insert_iterator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, char, std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>>(__out_it=(container = ""), __fmt="hello {}", __args=basic_format_args<std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char> >, char> > @ 0x0000ffffffffe808) at format_functions.h:387:5
    frame #15: 0x0000aaaaaabd6ee4 t.tmp.exe`void std::__1::__print::__vprint_nonunicode[abi:v170000]<void>(_IO_FILE*, std::__1::basic_string_view<char, std::__1::char_traits<char>>, std::__1::basic_format_args<std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>, bool) [inlined] std::__1::back_insert_iterator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>> std::__1::vformat_to[abi:v170000]<std::__1::back_insert_iterator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>>(__out_it=(container = ""), __fmt="hello {}", __args=std::__1::format_args @ 0x0000ffffffffe7a0) at format_functions.h:399:10
    frame #16: 0x0000aaaaaabd6e5c t.tmp.exe`void std::__1::__print::__vprint_nonunicode[abi:v170000]<void>(_IO_FILE*, std::__1::basic_string_view<char, std::__1::char_traits<char>>, std::__1::basic_format_args<std::__1::basic_format_context<std::__1::back_insert_iterator<std::__1::__format::__output_buffer<char>>, char>>, bool) [inlined] std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> std::__1::vformat[abi:v170000]<void>(__fmt="hello {}", __args=std::__1::format_args @ 0x0000ffffffffe730) at format_functions.h:432:3
    frame #17: 0x0000aaaaaabd6d3c t.tmp.exe`void std::__1::__print::__vprint_nonunicode[abi:v170000]<void>(__stream=0x0000e14000000000, __fmt="hello {}", __args=std::__1::format_args @ 0x0000ffffffffe8c8, __write_nl=false) at print:208:18
    frame #18: 0x0000aaaaaabd6850 t.tmp.exe`void std::__1::vprint_nonunicode[abi:v170000]<void>(__stream=0x0000e14000000000, __fmt="hello {}", __args=std::__1::format_args @ 0x0000ffffffffea38) at print:355:3
    frame #19: 0x0000aaaaaabc1510 t.tmp.exe`auto $_1::operator()<>(this=0x0000fffffffff2f6, what="Argument index out of bounds", fmt="hello {}") const at vprint_nonunicode.file.pass.cpp:57:3
    frame #20: 0x0000aaaaaabbb3f0 t.tmp.exe`void print_tests<$_0, $_1>(check=(unnamed class) @ 0x0000fffffffff2f7, check_exception=(unnamed class) @ 0x0000fffffffff2f6) at print_tests.h:78:3
    frame #21: 0x0000aaaaaabb9d9c t.tmp.exe`main((null)=1, (null)=0x0000fffffffff4e8) at vprint_nonunicode.file.pass.cpp:134:3
    frame #22: 0x0000fffff7ab4e18 libc.so.6`__libc_start_main(main=(t.tmp.exe`main at vprint_nonunicode.file.pass.cpp:133), argc=1, argv=0x0000fffffffff4e8, init=<unavailable>, fini=<unavailable>, rtld_fini=<unavailable>, stack_end=<unavailable>) at libc-start.c:308:16
    frame #23: 0x0000aaaaaab31df4 t.tmp.exe`_start + 52

[Mordante]

In D150044#4519677, @hctim wrote:

$ lldb /home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe
(lldb) target create "/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe"                                            Current executable set to '/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe' (aarch64).                            (lldb) r
Process 737940 launched: '/home/mitchp/build/libcxx_build_msan/test/std/input.output/iostream.format/print.fun/Output/vprint_nonunicode.file.pass.cpp.dir/t.tmp.exe' (aarch64)
Process 737940 stopped and restarted: thread 1 received signal: SIGCHLD
libc++abi: terminating due to uncaught exception of type std::__1::format_error: Argument index out of bounds
Process 737940 stopped
* thread #1, name = 't.tmp.exe', stop reason = signal SIGABRT
    frame #0: 0x0000fffff7ac7eac libc.so.6`__GI_raise(sig=6) at raise.c:51:1
(lldb) bt
* thread #1, name = 't.tmp.exe', stop reason = signal SIGABRT
  * frame #0: 0x0000fffff7ac7eac libc.so.6`__GI_raise(sig=6) at raise.c:51:1
    frame #1: 0x0000fffff7ab4aa0 libc.so.6`__GI_abort at abort.c:79:7
    frame #2: 0x0000fffff7dd4948 libc++abi.so.1`abort_message at abort_message.cpp:78:5
    frame #3: 0x0000fffff7d8a1f0 libc++abi.so.1`::demangling_terminate_handler() at cxa_default_handlers.cpp:72:9
    frame #4: 0x0000fffff7dd3138 libc++abi.so.1`std::__terminate(void (*)()) at cxa_handlers.cpp:59:9
    frame #5: 0x0000fffff7dda23c libc++abi.so.1`__cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) at cxa_exception.cpp:152:5
    frame #6: 0x0000fffff7dda168 libc++abi.so.1`::__cxa_throw() at cxa_exception.cpp:283:5
    frame #7: 0x0000aaaaaabdbfac t.tmp.exe`std::__1::__throw_format_error[abi:v170000](__s="Argument index out of bounds") at format_error.h:41:3

This looks suspicious.
The code throws an exception which I verified is intended.
Then the libc++abi calls failed_throw which causes termination.
Is there a way to get more information about what happens in frame #6? Here it seems the exception is not able to find the proper handler for the exception and thus calling terminate.

[Mordante]

libcxx/src/print.cpp

55

D156019 is the followup.

[rprichard]

libcxx/include/print

216

I'm wondering about this usage of std::ferror. The first argument to std::__throw_system_error appears to be a Unix errno value, whereas ferror appears to returns non-zero if the stream's error indicator flag is set.

e.g. The (print.file.pass.cpp, test_read_only) test opens a read-only file and tries to print to it. fwrite to such a stream fails with EBADF(9). glibc sets the stream's error indicator, so ferror returns 1, which is interpreted as EPERM(1). With Bionic, ferror instead returns 0, so this test is failing on Bionic/Android, because there is no OS error string suffixed to the what() result.

[uabelho]

libcxx/test/libcxx/input.output/iostream.format/print.fun/vprint_unicode_posix.pass.cpp

40

When I run this testcase the assert on line 48 below fails for me, and it seems to be because the "fmemopen" call here writes '\0' at the first byte in buffer.

I really doen't know anything about this and if I read at
https://man7.org/linux/man-pages/man3/fmemopen.3.html
it says

w      The stream is opened for writing.

and also

w+     Open the stream for reading and writing.  The buffer
       contents are truncated (i.e., '\0' is placed in the first
       byte of the buffer).

So it seems like when I run this in my environment "w" partly does what "w+" should do.

Does this problem sound familiar to anyone?

[tahonermann]

libcxx/test/libcxx/input.output/iostream.format/print.fun/vprint_unicode_posix.pass.cpp

40

Are you by chance using an old glibc version from 2015 or earlier? Early implementations of fmemopen() unconditionally truncated the buffer when opened for write. This was changed in this commit:

• https://github.com/bminor/glibc/commit/fdb7d390dd0d96e4a8239c46f3aa64598b90842b#diff-d190e07e0c146d56444d64c78bb49f4764974719ed454e0254644e1a7b793803L239

Alternatively, the "old" implementation replaced by the commit above is still present in current glibc releases under the name __old_fmemopen. Perhaps your builds are somehow calling that implementation?

• https://github.com/bminor/glibc/blob/master/libio/oldfmemopen.c

[uabelho]

libcxx/test/libcxx/input.output/iostream.format/print.fun/vprint_unicode_posix.pass.cpp

40

Yes, seems like we're using ancient glibc versions on our servers.

That explains our problem then. Thank you!

[ldionne]

libcxx/include/print

216

See https://reviews.llvm.org/D158930