I have found a bug in the gcc cross-compiler supplied in eldk-4.2 for
ppc_4xxFP-gcc. (Available from http://denx.de)
I noticed that the dumpe2fs program segfaulted on my sequoia powerpc evaluation
board (running Linux with nfs as the rootfs). After a lot of detective work, I
have produced a small program that illustrates the problem.
I'll attach the .i file along with the -v output. I'll also attach a dump of
the executable.
The bug is that the compiler collapses two "if" tests together, but in doing
so, it tests a value before assigning to it.
The two "if" statements are:
if (!*pp) /* function ext2fs_get_mem */
if (!bb->list) { /* function make_u32_list */
The following section of the dump shows the problem (this correlates to the
second malloc in routine make_u32_list():
100004c4: 48 04 05 d5 bl 10040a98 <[EMAIL PROTECTED]>
100004c8: 81 61 00 08 lwz r11,8(r1)
100004cc: 7c 60 fe 70 srawi r0,r3,31
100004d0: 7c 09 1a 78 xor r9,r0,r3
100004d4: 83 eb 00 0c lwz r31,12(r11) /* copies bb->list into
r31 too early */
100004d8: 7d 29 00 50 subf r9,r9,r0
100004dc: 3c 00 80 d4 lis r0,-32556
100004e0: 7d 3d fe 70 srawi r29,r9,31
100004e4: 60 00 48 ba ori r0,r0,18618
100004e8: 2f 9f 00 00 cmpwi cr7,r31,0 /* tests uninitialized
version of bb->list */
100004ec: 7f bd 00 38 and r29,r29,r0
100004f0: 3d 3d 7f 2c addis r9,r29,32556
100004f4: 90 7c 00 0c stw r3,12(r28) /* bb->list finally
receives malloc pointer here */
At 100004c4 we call malloc, and the return value is in r3. The "if"
test appears at 100004e8 and checks r31. Looking back at 100004d4 we
see bb->list is loaded into r31. However, r3 is not loaded into bb->list
until 100004f4, long after bb->list has been used.
--
Summary: Incorrect code generated - value tested before it is
set.
Product: gcc
Version: 4.2.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sfalco at harris dot com
GCC host triplet: i686-host_pc-linux-gnu
GCC target triplet: powerpc-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36775
