vm: bound trace data printing

[fallintoplace]

Summary

• replace unbounded VM trace string appends with checked vsnprintf-backed helpers
• cap printed memory event data at the existing 2048-byte stack buffer contract
• add a large trace-data print regression case with event_data_max greater than 2048

Root cause

fd_vm_trace_printf() sized its stack buffer for 2048 printable data bytes, but data_sz came from trace->event_data_max. A larger trace data cap let the memory dump loop write past the buffer through unbounded fd_cstr_append_printf() / vsprintf calls.

Validation

• git diff --check
• clang -std=c17 -fsyntax-only -I. -D_XOPEN_SOURCE=700 -DFD_HAS_HOSTED=1 -DFD_HAS_INT128=1 -DFD_HAS_DOUBLE=1 -DFD_HAS_ALLOCA=1 src/flamenco/vm/fd_vm_trace.c
• clang -std=c17 -fsyntax-only -I. -D_XOPEN_SOURCE=700 -DFD_HAS_HOSTED=1 -DFD_HAS_INT128=1 -DFD_HAS_DOUBLE=1 -DFD_HAS_ALLOCA=1 src/flamenco/vm/test_vm_base.c

Could not run gmake -j test_vm_base locally on macOS: the native make path hits BSD grep -P and does not expose a test_vm_base target in this environment.

[greptile-jt]

Prompt To Fix All With AI

This is a comment left during a code review.
Path: src/flamenco/vm/fd_vm_trace.c
Line: 11-15

Comment:
**Missing format attribute for compile-time checking**

`fd_cstr_append_printf` in this codebase declares `__attribute__((format(printf,2,3)))` to enable compile-time format string validation (see `fd_cstr.h:240`). This new variadic helper should do the same to catch format/argument mismatches at compile time.

```suggestion
static int
fd_vm_trace_printf_append( char **      p,
                           char *       end,
                           char const * fmt,
                           ... ) __attribute__((format(printf,3,4)));
static int
fd_vm_trace_printf_append( char **      p,
                           char *       end,
                           char const * fmt,
                           ... ) {
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "vm: bound trace data printing" | Re-trigger Greptile}

[greptile-jt]

Missing format attribute for compile-time checking

fd_cstr_append_printf in this codebase declares __attribute__((format(printf,2,3))) to enable compile-time format string validation (see fd_cstr.h:240). This new variadic helper should do the same to catch format/argument mismatches at compile time.

Suggested change

	static int
	fd_vm_trace_printf_append( char ** p,
	char * end,
	char const * fmt,
	... ) {
	static int
	fd_vm_trace_printf_append( char ** p,
	char * end,
	char const * fmt,
	... ) __attribute__((format(printf,3,4)));
	static int
	fd_vm_trace_printf_append( char ** p,
	char * end,
	char const * fmt,
	... ) {

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/flamenco/vm/fd_vm_trace.c
Line: 11-15

Comment:
**Missing format attribute for compile-time checking**

`fd_cstr_append_printf` in this codebase declares `__attribute__((format(printf,2,3)))` to enable compile-time format string validation (see `fd_cstr.h:240`). This new variadic helper should do the same to catch format/argument mismatches at compile time.

```suggestion
static int
fd_vm_trace_printf_append( char **      p,
                           char *       end,
                           char const * fmt,
                           ... ) __attribute__((format(printf,3,4)));
static int
fd_vm_trace_printf_append( char **      p,
                           char *       end,
                           char const * fmt,
                           ... ) {
```

How can I resolve this? If you propose a fix, please make it concise.

[greptile-jt]

_{Reviews (2): Last reviewed commit: "vm: add trace printf format checking" | Re-trigger Greptile}