Re: [PATCH v3 12/13] tracing: Check for printable characters when printing field dyn strings
From: Douglas Raillard <hidden>
Date: 2025-10-20 12:19:52
Also in:
linux-perf-users, lkml
Hi Steve, On 15-10-2025 18:32, Steven Rostedt wrote:
From: Steven Rostedt <rostedt@goodmis.org> When the "fields" option is enabled, it prints each trace event field based on its type. But a dynamic array and a dynamic string can both have a "char *" type. Printing it as a string can cause escape characters to be printed and mess up the output of the trace.
We faced the same issue when converting trace.dat to other formats that distinguish between a byte buffer and an actual string. The current solution we have is to reserve "char []" for actual string and use "u8 []"/"uint8_t []" for byte buffers. Obviously it does not solve the problem for existing events but that could be worth establishing a convention like that for new code and support it in trace_output.c ? Most uses of trace data beyond direct printing would require knowing the data schema from the header info, so value-based criteria are typically not suitable for that.
quoted hunk ↗ jump to hunk
For dynamic strings, test if there are any non-printable characters, and if so, print both the string with the non printable characters as '.', and the print the hex value of the array. Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> --- kernel/trace/trace_output.c | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-)diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 97db0b0ccf3e..718b255b6fd8 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c@@ -950,7 +950,9 @@ static void print_fields(struct trace_iterator *iter, struct trace_event_call *c int offset; int len; int ret; + int i; void *pos; + char *str; list_for_each_entry_reverse(field, head, link) { trace_seq_printf(&iter->seq, " %s=", field->name);@@ -977,8 +979,29 @@ static void print_fields(struct trace_iterator *iter, struct trace_event_call *c trace_seq_puts(&iter->seq, "<OVERFLOW>"); break; } - pos = (void *)iter->ent + offset; - trace_seq_printf(&iter->seq, "%.*s", len, (char *)pos); + str = (char *)iter->ent + offset; + /* Check if there's any non printable strings */ + for (i = 0; i < len; i++) { + if (str[i] && !(isascii(str[i]) && isprint(str[i]))) + break; + } + if (i < len) { + for (i = 0; i < len; i++) { + if (isascii(str[i]) && isprint(str[i])) + trace_seq_putc(&iter->seq, str[i]); + else + trace_seq_putc(&iter->seq, '.'); + } + trace_seq_puts(&iter->seq, " ("); + for (i = 0; i < len; i++) { + if (i) + trace_seq_putc(&iter->seq, ':'); + trace_seq_printf(&iter->seq, "%02x", str[i]); + } + trace_seq_putc(&iter->seq, ')'); + } else { + trace_seq_printf(&iter->seq, "%.*s", len, str); + } break; case FILTER_PTR_STRING: if (!iter->fmt_size)
-- Douglas