libDtHelp is unable to read SDL help files
with -ftree-store-ccp optimization which
is enabled by -O2 on gcc 4.2.1.
GifUtils.c and decompress.c didn't work
properly with -ftree-store-ccp enabled.
GifUtils.c was repaired by fixing
those warnings:
GifUtils.c: In function 'create_pixmap':
GifUtils.c:1093: warning: return makes integer from pointer without a cast
GifUtils.c:1110: warning: return makes integer from pointer without a cast
GifUtils.c:1215: warning: return makes integer from pointer without a cast
GifUtils.c: In function 'gif_to_pixmap':
GifUtils.c:1242: warning: return makes integer from pointer without a cast
decompress.c didn't generate warnings, but the
only effect of the -ftree-store-cpp was to introduce
this change:
addq $1, %rax
movq %rax, (%rbx)
.L90:
- cmpl $157, %edx
+ cmpl $-99, %edx
jne .L86
movl 8(%rbx), %eax
subl $1, %eax
Which corresponds to this source code:
bufioI.h
57 #define BufFileGet(f) ((f)->left-- ? *(f)->bufp++ : (*(f)->io) (f))
42 int (*io)(/* BufFilePtr f */);
decompress.c
53 #ifdef NO_UCHAR
54 typedef char char_type;
55 #else
56 typedef unsigned char char_type;
57 #endif /* UCHAR */
58
59 static char_type magic_header[] = { "\037\235" }; /* 1F 9D */
131 if ((BufFileGet(f) != (magic_header[0] & 0xFF)) ||
132 (BufFileGet(f) != (magic_header[1] & 0xFF)))
133 {
134 return 0;
135 }
BufFileGet() returns (int), so the (unsigned char) constants
got promoted to (int) with sign extension; therefore constant
157 decimal (0x9D) became -99 decimal, sign extended
(0xffffff9D), and the comparison was always false.
Tested using:
$ gcc -v
Using built-in specs.
Target: amd64-undermydesk-freebsd
Configured with: FreeBSD/amd64 system compiler
Thread model: posix
gcc version 4.2.1 20070831 patched [FreeBSD]
Running on:
FreeBSD 10.0-CURRENT (r240948M)
built Wed Sep 26 23:33:08 CEST 2012
Peter Howkins