* Re: [PATCH] tools: Use fputc() calls in some functions
[not found] <48f2d61f-d468-49b7-881e-f00777db073f@web.de>
[not found] ` <amIbVOIsOeZgcBZF@tassilo>
@ 2026-07-23 15:07 ` bot+bpf-ci
2026-08-06 17:40 ` kernel test robot
2026-08-06 21:50 ` kernel test robot
3 siblings, 0 replies; 6+ messages in thread
From: bot+bpf-ci @ 2026-07-23 15:07 UTC (permalink / raw)
To: Markus.Elfring, acpica-devel, bpf, coresight, kvm, linux-acpi,
linux-arm-kernel, linux-gpio, linux-kselftest, linux-mm,
linux-perf-users, linux-pm, linux-trace-kernel, linuxppc-dev,
mptcp, netdev, platform-driver-x86, virtualization, adrian.hunter,
amastro, alex, alexander.shishkin, ast, ak, andrew+netdev, akpm,
andrii, ankur.a.arora, acme, brgl, bobbyeshleman, borntraeger,
chleroy, ctshao, imbrenda, costa.shul, crwood, daniel,
daniel.lezcano, david, dmatlack, davem
Cc: linux-kernel, kernel-janitors, ast, andrii, daniel, martin.lau,
eddyz87, yonghong.song, clm, ihor.solodrai
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> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> --- a/tools/bpf/bpftool/common.c
> +++ b/tools/bpf/bpftool/common.c
> @@ -53,7 +53,7 @@ void p_err(const char *fmt, ...)
> } else {
> fprintf(stderr, "Error: ");
> vfprintf(stderr, fmt, ap);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
^^^^^^
The fputc() arguments are reversed. The C standard signature is
`int fputc(int c, FILE *stream)` - the character comes first, the stream
second. This passes the FILE* stderr as the int c parameter and '\n' as
the FILE* stream parameter.
Correct form is `fputc('\n', stderr)`.
This constraint violation triggers a -Werror=int-conversion diagnostic and
breaks the build. If it compiled, at runtime fputc would dereference
(FILE*)10, crashing the program.
The same argument reversal occurs in 67 conversions across this patch.
> @@ -67,7 +67,7 @@ void p_info(const char *fmt, ...)
>
> va_start(ap, fmt);
> vfprintf(stderr, fmt, ap);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
^^^^^^
Same reversed-argument bug.
> diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
> --- a/tools/bpf/bpftool/main.c
> +++ b/tools/bpf/bpftool/main.c
> @@ -273,7 +273,7 @@ void fprint_hex(FILE *f, void *arg, unsigned int n, const char *sep)
> if (!i)
> /* nothing */;
> else if (!(i % 16))
> - fprintf(f, "\n");
> + fputc(f, '\n');
Arguments reversed: `fputc(f, '\n')` should be `fputc('\n', f)`.
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1266,7 +1266,7 @@ static void hex_print(void *data, unsigned int size, FILE *f)
> fprintf(f, "%c%s", c, j == i + 7 ? " " : "");
> }
>
> - fprintf(f, "\n");
> + fputc(f, '\n');
Arguments reversed.
> diff --git a/tools/include/nolibc/err.h b/tools/include/nolibc/err.h
> --- a/tools/include/nolibc/err.h
> +++ b/tools/include/nolibc/err.h
> @@ -27,7 +27,7 @@ void vwarnx(const char *fmt, va_list args)
> {
> fprintf(stderr, "%s: ", program_invocation_short_name);
> vfprintf(stderr, fmt, args);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed. This is in a nolibc header - nolibc's fputc
(tools/include/nolibc/stdio.h) does `write(fileno(stream), &ch, 1)`.
With stream==(FILE*)10 fileno dereferences a bogus pointer and crashes.
> diff --git a/tools/mm/page_owner_sort.c b/tools/mm/page_owner_sort.c
> --- a/tools/mm/page_owner_sort.c
> +++ b/tools/mm/page_owner_sort.c
> @@ -867,7 +867,7 @@ struct option longopts[] = {
> }
> if (cull & CULL_STACKTRACE)
> fprintf(fout, ":\n%s", list[i].stacktrace);
> - fprintf(fout, "\n");
> + fputc(fout, '\n');
Arguments reversed: should be `fputc('\n', fout)`.
> diff --git a/tools/net/ynl/ynltool/main.c b/tools/net/ynl/ynltool/main.c
> --- a/tools/net/ynl/ynltool/main.c
> +++ b/tools/net/ynl/ynltool/main.c
> @@ -156,7 +156,7 @@ void p_err(const char *fmt, ...)
> } else {
> fprintf(stderr, "Error: ");
> vfprintf(stderr, fmt, ap);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> }
> va_end(ap);
> }
> @@ -170,7 +170,7 @@ void p_info(const char *fmt, ...)
>
> va_start(ap, fmt);
> vfprintf(stderr, fmt, ap);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Both conversions reverse the arguments.
> diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
> --- a/tools/objtool/builtin-check.c
> +++ b/tools/objtool/builtin-check.c
> @@ -297,7 +297,7 @@ int make_backup(void)
> fprintf(stderr, " %s", arg);
> }
>
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed. objtool runs during the kernel build, so a build
failure or crash here breaks the build.
> diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
> --- a/tools/objtool/disas.c
> +++ b/tools/objtool/disas.c
> @@ -537,7 +537,7 @@ void disas_print_insn(FILE *stream, struct disas_context *dctx,
> return;
>
> if (strcmp(format, "\n") == 0) {
> - fprintf(stream, "\n");
> + fputc(stream, '\n');
Arguments reversed.
> diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c
> --- a/tools/perf/builtin-c2c.c
> +++ b/tools/perf/builtin-c2c.c
> @@ -2511,7 +2511,7 @@ struct perf_hpp hpp = {
> hists__fprintf_headers(&c2c_hists->hists, out);
> once = true;
> } else {
> - fprintf(out, "\n");
> + fputc(out, '\n');
> }
[ ... ]
> @@ -2590,15 +2590,15 @@ static void perf_c2c__hists_fprintf(FILE *out, struct perf_session *session)
> setup_pager();
>
> print_c2c__display_stats(out);
> - fprintf(out, "\n");
> + fputc(out, '\n');
> print_shared_cacheline_info(out);
> - fprintf(out, "\n");
> + fputc(out, '\n');
> print_c2c_info(out, session);
>
> if (c2c.stats_only)
> return;
>
> - fprintf(out, "\n");
> + fputc(out, '\n');
[ ... ]
> @@ -2606,7 +2606,7 @@ static void perf_c2c__hists_fprintf(FILE *out, struct perf_session *session)
>
> hists__fprintf(&c2c.hists.hists, true, 0, 0, 0, stdout, true);
>
> - fprintf(out, "\n");
> + fputc(out, '\n');
All four conversions reverse the arguments.
> diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
> --- a/tools/perf/builtin-daemon.c
> +++ b/tools/perf/builtin-daemon.c
> @@ -691,7 +691,7 @@ static int cmd_session_list(struct daemon *daemon, union cmd *cmd, FILE *out)
> /* session up time */
> csv_sep, (uint64_t)((curr - daemon->start) / 60));
>
> - fprintf(out, "\n");
> + fputc(out, '\n');
> } else {
[ ... ]
> @@ -730,7 +730,7 @@
> /* session up time */
> csv_sep, (uint64_t)((curr - session->start) / 60));
>
> - fprintf(out, "\n");
> + fputc(out, '\n');
Both conversions reverse the arguments.
> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
> --- a/tools/perf/builtin-lock.c
> +++ b/tools/perf/builtin-lock.c
> @@ -1319,9 +1319,9 @@ static void print_result(void)
>
> list_for_each_entry(key, &lock_keys, list) {
> key->print(key, st);
> - fprintf(lock_output, " ");
> + fputc(lock_output, ' ');
> }
> - fprintf(lock_output, "\n");
> + fputc(lock_output, '\n');
Both `fputc(lock_output, ' ')` and `fputc(lock_output, '\n')` reverse the
arguments. Correct form: `fputc(' ', lock_output)` and
`fputc('\n', lock_output)`.
> @@ -1598,7 +1598,7 @@ static void print_header_csv(const char *sep)
> fprintf(lock_output, "%s%s %s", "type", sep, "caller");
> if (verbose > 0)
> fprintf(lock_output, "%s %s", sep, "stacktrace");
> - fprintf(lock_output, "\n");
> + fputc(lock_output, '\n');
[ ... ]
> @@ -1629,7 +1629,7 @@ static void print_lock_stat_stdio(struct lock_contention *con, struct lock_stat *st)
>
> list_for_each_entry(key, &lock_keys, list) {
> key->print(key, st);
> - fprintf(lock_output, " ");
> + fputc(lock_output, ' ');
> }
[ ... ]
> @@ -1687,7 +1687,7 @@ static void print_lock_stat_csv(struct lock_contention *con, struct lock_stat *st,
> case LOCK_AGGR_CALLER:
> fprintf(lock_output, "%s%s %s", get_type_flags_name(st->flags), sep, st->name);
> if (verbose <= 0)
> - fprintf(lock_output, "\n");
> + fputc(lock_output, '\n');
[ ... ]
> @@ -1721,7 +1721,7 @@ static void print_lock_stat_csv(struct lock_contention *con, struct lock_stat *st,
> get_symbol_name_offset(kmap, sym, ip, buf, sizeof(buf));
> fprintf(lock_output, "%s %#lx %s", i ? ":" : sep, (unsigned long) ip, buf);
> }
> - fprintf(lock_output, "\n");
> + fputc(lock_output, '\n');
> }
> }
[ ... ]
> @@ -1781,7 +1781,7 @@ static void print_footer_csv(int total, int bad, struct lock_contention_fails *fails,
> for (i = 0; i < BROKEN_MAX; i++)
> fprintf(lock_output, "%s bad_%s=%d", sep, name[i], bad_hist[i]);
> }
> - fprintf(lock_output, "\n");
> + fputc(lock_output, '\n');
All six conversions in builtin-lock.c reverse the arguments.
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -2561,7 +2561,7 @@
>
> perf_sample__fprintf_ipc(sample, evsel, fp);
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
[ ... ]
> @@ -2815,7 +2815,7 @@
> cursor, symbol_conf.bt_stop_list, fp);
> }
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
[ ... ]
> @@ -3271,11 +3271,11 @@ static int list_available_languages_cb(struct scripting_ops *ops, const char *spec)
>
> static void list_available_languages(void)
> {
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> fprintf(stderr, "Scripting language extensions (used in "
> "perf script -s [spec:]script.[spec]):\n\n");
> script_spec__for_each(&list_available_languages_cb);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
All four conversions reverse the arguments.
> diff --git a/tools/perf/ui/gtk/util.c b/tools/perf/ui/gtk/util.c
> --- a/tools/perf/ui/gtk/util.c
> +++ b/tools/perf/ui/gtk/util.c
> @@ -37,7 +37,7 @@ static int perf_gtk__error(const char *format, va_list args)
> vasprintf(&msg, format, args) < 0) {
> fprintf(stderr, "Error:\n");
> vfprintf(stderr, format, args);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> return -1;
> }
>
> @@ -62,7 +62,7 @@ static int perf_gtk__warning_info_bar(const char *format, va_list args)
> vasprintf(&msg, format, args) < 0) {
> fprintf(stderr, "Warning:\n");
> vfprintf(stderr, format, args);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> return -1;
> }
>
> @@ -83,7 +83,7 @@ static int perf_gtk__warning_statusbar(const char *format, va_list args)
> vasprintf(&msg, format, args) < 0) {
> fprintf(stderr, "Warning:\n");
> vfprintf(stderr, format, args);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
All three conversions reverse the arguments.
> diff --git a/tools/perf/ui/stdio/hist.c b/tools/perf/ui/stdio/hist.c
> --- a/tools/perf/ui/stdio/hist.c
> +++ b/tools/perf/ui/stdio/hist.c
> @@ -691,7 +691,7 @@
> }
>
> next_line:
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
> }
[ ... ]
> @@ -783,7 +783,7 @@ hists__fprintf_standard_headers(struct hists *hists,
> if (line)
> fprintf(fp, "# ");
> fprintf_line(hists, hpp, line, fp);
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
> }
[ ... ]
> @@ -806,10 +806,10 @@ hists__fprintf_standard_headers(struct hists *hists,
>
> width = fmt->width(fmt, hpp, hists);
> for (i = 0; i < width; i++)
> - fprintf(fp, ".");
> + fputc(fp, '.');
> }
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
All four conversions reverse the arguments.
> diff --git a/tools/perf/util/debug.c b/tools/perf/util/debug.c
> --- a/tools/perf/util/debug.c
> +++ b/tools/perf/util/debug.c
> @@ -350,7 +350,7 @@ void __dump_stack(FILE *file, void **stackdump, size_t stackdump_size)
> fprintf(file, " #%zd %p ", i, stackdump[i]);
>
> map__fprintf_srcline(al.map, al.addr, "", file);
> - fprintf(file, "\n");
> + fputc(file, '\n');
Arguments reversed.
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -2454,7 +2454,7 @@ static void __print_pmu_caps(FILE *fp, int nr_caps, char **caps, char *pmu_name)
> delimiter = ", ";
> }
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
> }
[ ... ]
> @@ -2513,7 +2513,7 @@ static void print_pmu_mappings(struct feat_fd *ff, FILE *fp)
> pmu_num--;
> }
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
[ ... ]
> @@ -4349,7 +4349,7 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
> fprintf(fp, "%s ", feat_ops[bit].name);
> }
>
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
All three conversions reverse the arguments.
> diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-log.c b/tools/perf/util/intel-pt-decoder/intel-pt-log.c
> --- a/tools/perf/util/intel-pt-decoder/intel-pt-log.c
> +++ b/tools/perf/util/intel-pt-decoder/intel-pt-log.c
> @@ -70,14 +70,14 @@ static void intel_pt_print_data(const unsigned char *buf, int len, uint64_t pos,
> int i;
>
> for (i = 0; i < indent; i++)
> - fprintf(f, " ");
> + fputc(f, ' ');
>
> fprintf(f, " %08" PRIx64 ": ", pos);
> for (i = 0; i < len; i++)
> fprintf(f, " %02x", buf[i]);
> for (; i < 16; i++)
> fprintf(f, " ");
> - fprintf(f, " ");
> + fputc(f, ' ');
> }
>
> static void intel_pt_print_no_data(uint64_t pos, int indent)
> @@ -85,12 +85,12 @@ static void intel_pt_print_no_data(uint64_t pos, int indent)
> int i;
>
> for (i = 0; i < indent; i++)
> - fprintf(f, " ");
> + fputc(f, ' ');
>
> fprintf(f, " %08" PRIx64 ": ", pos);
> for (i = 0; i < 16; i++)
> fprintf(f, " ");
> - fprintf(f, " ");
> + fputc(f, ' ');
> }
All four conversions reverse the arguments.
> diff --git a/tools/perf/util/libbfd.c b/tools/perf/util/libbfd.c
> --- a/tools/perf/util/libbfd.c
> +++ b/tools/perf/util/libbfd.c
> @@ -603,7 +603,7 @@
> } else
> srcline = NULL;
>
> - fprintf(s, "\n");
> + fputc(s, '\n');
Arguments reversed. The variable s is an open_memstream() stream.
> diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> --- a/tools/perf/util/stat-display.c
> +++ b/tools/perf/util/stat-display.c
> @@ -529,7 +529,7 @@ static void print_metric_json(struct perf_stat_config *config __maybe_unused,
> }
> }
> if (!config->metric_only)
> - fprintf(out, "}");
> + fputc(out, '}');
> }
[ ... ]
> @@ -1316,7 +1316,7 @@ static void print_header_std(struct perf_stat_config *config,
> FILE *output = config->output;
> int i;
>
> - fprintf(output, "\n");
> + fputc(output, '\n');
> fprintf(output, " Performance counter stats for ");
[ ... ]
> @@ -1333,7 +1333,7 @@ static void print_header_std(struct perf_stat_config *config,
> else
> fprintf(output, "thread id \'%s", _target->tid);
>
> - fprintf(output, "\'");
> + fputc(output, '\'');
[ ... ]
> @@ -1406,9 +1406,9 @@ static void print_table(struct perf_stat_config *config, FILE *output, double avg)
> fprintf(output, " %17.9f (%+.9f) ", run, run - avg);
>
> for (h = 0; h < n; h++)
> - fprintf(output, "#");
> + fputc(output, '#');
>
> - fprintf(output, "\n");
> + fputc(output, '\n');
> }
[ ... ]
> @@ -1428,7 +1428,7 @@ static void print_footer(struct perf_stat_config *config)
> return;
>
> if (!config->null_run)
> - fprintf(output, "\n");
> + fputc(output, '\n');
All six conversions reverse the arguments.
> diff --git a/tools/perf/util/values.c b/tools/perf/util/values.c
> --- a/tools/perf/util/values.c
> +++ b/tools/perf/util/values.c
> @@ -217,7 +217,7 @@ static void perf_read_values__display_pretty(FILE *fp,
> fprintf(fp, "# %*s %*s", pidwidth, "PID", tidwidth, "TID");
> for (j = 0; j < values->num_counters; j++)
> fprintf(fp, " %*s", counterwidth[j], evsel__name(values->counters[j]));
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
[ ... ]
> @@ -225,7 +225,7 @@ static void perf_read_values__display_pretty(FILE *fp,
> for (j = 0; j < values->num_counters; j++)
> fprintf(fp, " %*" PRIu64,
> counterwidth[j], values->value[i][j]);
> - fprintf(fp, "\n");
> + fputc(fp, '\n');
Both conversions reverse the arguments.
> diff --git a/tools/power/acpi/tools/acpidump/apdump.c b/tools/power/acpi/tools/acpidump/apdump.c
> --- a/tools/power/acpi/tools/acpidump/apdump.c
> +++ b/tools/power/acpi/tools/acpidump/apdump.c
> @@ -171,7 +171,7 @@ ap_dump_table_buffer(struct acpi_table_header *table,
> acpi_ut_dump_buffer_to_file(gbl_output_file,
> ACPI_CAST_PTR(u8, table), table_length,
> DB_BYTE_DISPLAY, 0);
> - fprintf(gbl_output_file, "\n");
> + fputc(gbl_output_file, '\n');
Arguments reversed.
> diff --git a/tools/power/x86/intel-speed-select/isst-display.c b/tools/power/x86/intel-speed-select/isst-display.c
> --- a/tools/power/x86/intel-speed-select/isst-display.c
> +++ b/tools/power/x86/intel-speed-select/isst-display.c
> @@ -122,7 +122,7 @@ static void format_and_print(FILE *outf, int level, char *header, char *value)
>
> if (level == 0) {
> if (header)
> - fprintf(outf, "{");
> + fputc(outf, '{');
[ ... ]
> @@ -138,7 +138,7 @@ static void format_and_print(FILE *outf, int level, char *header, char *value)
>
> if (value) {
> if (last_level != level)
> - fprintf(outf, "\n");
> + fputc(outf, '\n');
[ ... ]
> @@ -156,7 +156,7 @@ static void format_and_print(FILE *outf, int level, char *header, char *value)
> fprintf(outf, "\n%s}", delimiters);
> }
> if (abs(last_level - level) < 3)
> - fprintf(outf, "\n");
> + fputc(outf, '\n');
All three conversions reverse the arguments.
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -9099,7 +9099,7 @@ void dump_cpuid_hypervisor(void)
> dump_word_chars(ebx);
> dump_word_chars(ecx);
> dump_word_chars(edx);
> - fprintf(outf, "\n");
> + fputc(outf, '\n');
> }
[ ... ]
> @@ -9749,7 +9749,7 @@
> fprintf(outf, " siblings");
> for (ht_id = 0; ht_id <= MAX_HT_ID; ++ht_id)
> fprintf(outf, " %d", cpus[i].ht_sibling_cpu_id[ht_id]);
> - fprintf(outf, "\n");
> + fputc(outf, '\n');
Both conversions reverse the arguments.
> diff --git a/tools/testing/selftests/bpf/benchs/bench_htab_mem.c b/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
> --- a/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
> +++ b/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
> @@ -148,7 +148,7 @@ static const struct htab_mem_use_case *htab_mem_find_use_case_or_exit(const char *name)
> fprintf(stderr, "available use case:");
> for (i = 0; i < ARRAY_SIZE(use_cases); i++)
> fprintf(stderr, " %s", use_cases[i].name);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/bpf/jit_disasm_helpers.c b/tools/testing/selftests/bpf/jit_disasm_helpers.c
> --- a/tools/testing/selftests/bpf/jit_disasm_helpers.c
> +++ b/tools/testing/selftests/bpf/jit_disasm_helpers.c
> @@ -228,7 +228,7 @@ struct bpf_prog_info info = {};
> for (pc = 0, i = 0; i < jited_funcs; ++i) {
> fprintf(text_out, "func #%d:\n", i);
> disasm_one_func(text_out, image + pc, func_lens[i]);
> - fprintf(text_out, "\n");
> + fputc(text_out, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -383,7 +383,7 @@ static void print_test_result(const struct prog_test_def *test, const struct test_state *test_state)
> else
> fprintf(env.stdout_saved, "OK (SKIP: %d/%d)", skipped_cnt, subtests_cnt);
>
> - fprintf(env.stdout_saved, "\n");
> + fputc(env.stdout_saved, '\n');
> }
[ ... ]
> @@ -391,7 +391,7 @@ static void print_test_log(char *log_buf, size_t log_cnt)
> log_buf[log_cnt] = '\0';
> fprintf(env.stdout_saved, "%s", log_buf);
> if (log_buf[log_cnt - 1] != '\n')
> - fprintf(env.stdout_saved, "\n");
> + fputc(env.stdout_saved, '\n');
> }
[ ... ]
> @@ -409,7 +409,7 @@ static void print_subtest_name(int test_num, int subtest_num,
> if (result)
> fprintf(env.stdout_saved, ":%s", result);
>
> - fprintf(env.stdout_saved, "\n");
> + fputc(env.stdout_saved, '\n');
All three conversions reverse the arguments.
> diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> --- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> +++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> @@ -135,7 +135,7 @@ static void pr_err(const char *fmt, ...)
>
> if (errno != 0)
> fprintf(stderr, ": %s", strerror(errno));
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/kvm/s390/keyop.c b/tools/testing/selftests/kvm/s390/keyop.c
> --- a/tools/testing/selftests/kvm/s390/keyop.c
> +++ b/tools/testing/selftests/kvm/s390/keyop.c
> @@ -117,7 +117,7 @@ static void dump_sk(const unsigned char skeys[], const char *descr)
> fprintf(stderr, "# %3d: ", i);
> for (j = 0; j < 32; j++)
> fprintf(stderr, "%02x ", skeys[i + j]);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/net/mptcp/pm_nl_ctl.c b/tools/testing/selftests/net/mptcp/pm_nl_ctl.c
> --- a/tools/testing/selftests/net/mptcp/pm_nl_ctl.c
> +++ b/tools/testing/selftests/net/mptcp/pm_nl_ctl.c
> @@ -208,7 +208,7 @@
> }
> if (server_side)
> fprintf(stderr, ",server_side:1");
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/net/psock_tpacket.c b/tools/testing/selftests/net/psock_tpacket.c
> --- a/tools/testing/selftests/net/psock_tpacket.c
> +++ b/tools/testing/selftests/net/psock_tpacket.c
> @@ -116,7 +116,7 @@ static int pfsocket(int ver)
> static void status_bar_update(void)
> {
> if (total_packets % 10 == 0) {
> - fprintf(stderr, ".");
> + fputc(stderr, '.');
[ ... ]
> @@ -825,7 +825,7 @@ static int test_tpacket(int version, int type)
> unmap_ring(sock, &ring);
> close(sock);
>
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Both conversions reverse the arguments.
> diff --git a/tools/testing/selftests/net/txtimestamp.c b/tools/testing/selftests/net/txtimestamp.c
> --- a/tools/testing/selftests/net/txtimestamp.c
> +++ b/tools/testing/selftests/net/txtimestamp.c
> @@ -200,10 +200,10 @@ static void __print_timestamp(const char *name, struct timespec *cur,
> ts_delta = timespec_to_ns64(cur) - timespec_to_ns64(&ts_usr);
> fprintf(stderr, " (USR +");
> __print_ts_delta_formatted(ts_delta);
> - fprintf(stderr, ")");
> + fputc(stderr, ')');
> }
>
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> }
[ ... ]
> @@ -254,7 +254,7 @@ static void print_timing_event(char *name, struct timing_event *te)
> __print_ts_delta_formatted(te->min);
> fprintf(stderr, ", max=");
> __print_ts_delta_formatted(te->max);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> }
[ ... ]
> @@ -271,7 +271,7 @@ static void print_payload(char *data, int len)
> fprintf(stderr, "payload: ");
> for (i = 0; i < len; i++)
> fprintf(stderr, "%02hhx ", data[i]);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> }
[ ... ]
> @@ -933,7 +933,7 @@ int main(int argc, char **argv)
> fprintf(stderr, "protocol: %s\n", sock_names[cfg_proto]);
> fprintf(stderr, "payload: %u\n", cfg_payload_len);
> fprintf(stderr, "server port: %u\n", dest_port);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
All four conversions reverse the arguments.
> diff --git a/tools/testing/selftests/powerpc/nx-gzip/gunz_test.c b/tools/testing/selftests/powerpc/nx-gzip/gunz_test.c
> --- a/tools/testing/selftests/powerpc/nx-gzip/gunz_test.c
> +++ b/tools/testing/selftests/powerpc/nx-gzip/gunz_test.c
> @@ -363,7 +363,7 @@
> goto err3;
> fprintf(stderr, "%02x ", tmp[i]);
> if (i == 5)
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/assert.h b/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> --- a/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> +++ b/tools/testing/selftests/vfio/lib/include/libvfio/assert.h
> @@ -10,7 +10,7 @@ #define SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_ASSERT_H
>
> #define VFIO_LOG_AND_EXIT(...) do { \
> fprintf(stderr, " " __VA_ARGS__); \
> - fprintf(stderr, "\n"); \
> + fputc(stderr, '\n'); \
Arguments reversed in a widely-used macro. Every expansion of this macro
is broken.
> diff --git a/tools/testing/selftests/vfio/lib/libvfio.c b/tools/testing/selftests/vfio/lib/libvfio.c
> --- a/tools/testing/selftests/vfio/lib/libvfio.c
> +++ b/tools/testing/selftests/vfio/lib/libvfio.c
> @@ -60,16 +60,16 @@ char **vfio_selftests_get_bdfs(int *argc, char *argv[], int *nr_bdfs)
> }
>
> fprintf(stderr, "Unable to determine which device(s) to use, skipping test.\n");
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> fprintf(stderr, "To pass the device address via environment variable:\n");
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> fprintf(stderr, " export VFIO_SELFTESTS_BDF=\"segment:bus:device.function\"\n");
> fprintf(stderr, " %s [options]\n", argv[0]);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> fprintf(stderr, "To pass the device address(es) via argv:\n");
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
> fprintf(stderr, " %s [options] segment:bus:device.function ...\n", argv[0]);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
All five conversions reverse the arguments.
> diff --git a/tools/testing/vsock/vsock_diag_test.c b/tools/testing/vsock/vsock_diag_test.c
> --- a/tools/testing/vsock/vsock_diag_test.c
> +++ b/tools/testing/vsock/vsock_diag_test.c
> @@ -86,7 +86,7 @@ static void print_vsock_addr(FILE *fp, unsigned int cid, unsigned int port)
> fprintf(fp, "%u:", cid);
>
> if (port == VMADDR_PORT_ANY)
> - fprintf(fp, "*");
> + fputc(fp, '*');
[ ... ]
> @@ -94,7 +94,7 @@ static void print_vsock_addr(FILE *fp, unsigned int cid, unsigned int port)
> static void print_vsock_stat(FILE *fp, struct vsock_stat *st)
> {
> print_vsock_addr(fp, st->msg.vdiag_src_cid, st->msg.vdiag_src_port);
> - fprintf(fp, " ");
> + fputc(fp, ' ');
Both conversions reverse the arguments.
> diff --git a/tools/thermal/tmon/sysfs.c b/tools/thermal/tmon/sysfs.c
> --- a/tools/thermal/tmon/sysfs.c
> +++ b/tools/thermal/tmon/sysfs.c
> @@ -522,7 +522,7 @@ int update_thermal_data()
> }
>
> if (tmon_log) {
> - fprintf(tmon_log, "\n");
> + fputc(tmon_log, '\n');
Arguments reversed.
> diff --git a/tools/thermal/tmon/tmon.c b/tools/thermal/tmon/tmon.c
> --- a/tools/thermal/tmon/tmon.c
> +++ b/tools/thermal/tmon/tmon.c
> @@ -199,7 +199,7 @@
> fprintf(tmon_log, "%s%d ", ptdata.cdi[i].type,
> ptdata.cdi[i].instance);
>
> - fprintf(tmon_log, "\n");
> + fputc(tmon_log, '\n');
Arguments reversed.
> diff --git a/tools/tracing/latency/latency-collector.c b/tools/tracing/latency/latency-collector.c
> --- a/tools/tracing/latency/latency-collector.c
> +++ b/tools/tracing/latency/latency-collector.c
> @@ -1999,7 +1999,7 @@
> "been enabled. Random sleep is intended for the following tracers:\n");
> for (i = 0; random_tracers[i]; i++)
> fprintf(stderr, "%s\n", random_tracers[i]);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/tracing/rtla/src/common.c b/tools/tracing/rtla/src/common.c
> --- a/tools/tracing/rtla/src/common.c
> +++ b/tools/tracing/rtla/src/common.c
> @@ -449,7 +449,7 @@ void common_usage(const char *tool, const char *mode,
> fprintf(stderr, "%s [-h] ", mode);
>
> print_msg_array(start_msgs);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
> --- a/tools/tracing/rtla/src/utils.c
> +++ b/tools/tracing/rtla/src/utils.c
> @@ -67,7 +67,7 @@ void fatal(const char *fmt, ...)
> va_start(ap, fmt);
> vfprintf(stderr, fmt, ap);
> va_end(ap);
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/usb/ffs-test.c b/tools/usb/ffs-test.c
> --- a/tools/usb/ffs-test.c
> +++ b/tools/usb/ffs-test.c
> @@ -562,7 +562,7 @@ empty_out_buf(struct thread *ignore, const void *buf, size_t nbytes)
> fprintf(stderr, "%4zd:", len);
> fprintf(stderr, " %02x", *p);
> if (31 == (len % 32))
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
> diff --git a/tools/verification/rv/src/in_kernel.c b/tools/verification/rv/src/in_kernel.c
> --- a/tools/verification/rv/src/in_kernel.c
> +++ b/tools/verification/rv/src/in_kernel.c
> @@ -667,7 +667,7 @@ static void ikm_usage_print_reactors(void)
> end = strstr(start, "\n");
> }
>
> - fprintf(stderr, "\n");
> + fputc(stderr, '\n');
Arguments reversed.
Looking at the lore discussion by Andi Kleen and Steven Rostedt, they
raised a concern that GCC already performs this fprintf->fputc optimization
automatically, making the patch unnecessary code churn. The author has not
responded to this feedback.
Beyond the optimization question, the technical implementation has a
systematic bug: every fputc() conversion in this patch reverses the
argument order.
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/30016526959
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