Werror=format-security issue from gprofng/src/Print.cc

Yichao Yu yyc1992@gmail.com
Tue Jun 7 14:49:50 GMT 2022

I got a format-security werror on gprofng/src/Print.cc when trying to
build the master version of gdb (the compiler flag is added by the
archlinuxcn build machine).

While I could disable the flag, I think there might be a real issue
looking at the code.

The line that causes the issue is
which uses a "dynamic" format string without any argument. AFAICT, the
fmt3 is only ever initialized in
`er_print_experiment::overview_summary` and if I read it correctly,
it's initialized to a string with no actual formatting inputs other
than a `%%`. It is used, however, twice in
`er_print_experiment::overview_value`, one given two zeros as the
arguments and one given no arguments so it looks a bit suspicious.

The git log shows now history of this file so I'm not sure what's the
intention but my best guess is

1. the `fprintf (out_file, fmt3, 0., 0.);` was meant to be using
`fmt4`. (I assume this is to avoid nan from total_value = 0), or
2. since fmt3 is actually a string that's more or less "0.0 (0.0)"
with padding, the two `0.`s passed to fmt3 are probably bogus and it
should be the same as the `fprintf (out_file, fmt3);` below

if my understanding is correct, I think in either case one can simply
avoid using fmt3 with fprintf by just removing the extra % from it and
directly write it to the output instead. (i.e.
Did I miss anything?


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