https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106559
Bug ID: 106559
Summary: Spurious warning format-truncation (regression from 9)
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: phdiv at fastmail dot fm
Target Milestone: ---
Created attachment 53426
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53426&action=edit
Reproducer.
> cat w.cpp
extern char buffer[64];
extern unsigned int number[16];
void f(){
static const char string[16][3]={
"01","02","03","04","05","06","07","08",
"09","10","11","12","13","14","15","16"};
for(unsigned int i=0; i<16; ++i)
__builtin_snprintf(buffer,sizeof(buffer),"%u (%s): %8x",
i,string[i],number[i]);
}
> g++ -O1 -Wformat-truncation -c w.cpp
w.cpp: In function 'void f()':
w.cpp:10:61: warning: '__builtin_snprintf' output may be truncated before the
last format character [-Wformat-truncation=]
10 | __builtin_snprintf(buffer,sizeof(buffer),"%u (%s): %8x",
| ^
w.cpp:10:23: note: '__builtin_snprintf' output between 17 and 65 bytes into a
destination of size 64
10 | __builtin_snprintf(buffer,sizeof(buffer),"%u (%s): %8x",
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
11 | i,string[i],number[i]);
| ~~~~~~~~~~~~~~~~~~~~~~
Granted, the documentation of Wformat-truncation mentions possible false
positives, but this is a regression in GCC 10 with respect to GCC 9
(and present up to trunk).
For some more variations which do or do not exhibit this bug, see
https://godbolt.org/z/PvfrchP7E .
