From 907c42bcf0f06826279d5be91be7f7f9c45876d9 Mon Sep 17 00:00:00 2001 From: Simon Tatham Date: Sun, 1 Sep 2019 22:26:22 +0100 Subject: [PATCH] Fix build failure reported in gcc 9. Apparently gcc 9 is clever enough to say 'Hey, runtime field width in an sprintf targeting a fixed-size buffer!', but not clever enough to notice that the width was computed earlier as the max of lots of default-width sprintfs into the same buffer (so _either_ it's safe, or else - on a hypothetical platform with a 263-bit int - the damage was already done). Added a bounds check or two to keep it happy. --- twiddle.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/twiddle.c b/twiddle.c index 06f6ff1..07e2f81 100644 --- a/twiddle.c +++ b/twiddle.c @@ -550,6 +550,12 @@ static char *game_text_format(const game_state *state) int i, x, y, col, maxlen; bool o = state->orientable; + /* Pedantic check: ensure buf is large enough to format an int in + * decimal, using the bound log10(2) < 1/3. (Obviously in practice + * int is not going to be larger than even 32 bits any time soon, + * but.) */ + assert(sizeof(buf) >= 1 + sizeof(int) * CHAR_BIT/3); + /* * First work out how many characters we need to display each * number. We're pretty flexible on grid contents here, so we @@ -561,6 +567,11 @@ static char *game_text_format(const game_state *state) if (col < x) col = x; } + /* Reassure sprintf-checking compilers like gcc that the field + * width we've just computed is not now excessive */ + if (col >= sizeof(buf)) + col = sizeof(buf)-1; + /* * Now we know the exact total size of the grid we're going to * produce: it's got h rows, each containing w lots of col+o,