Public bug reported:
This GCC bug fix causes certain C code to miscompile
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002
It was a fixed a few months ago, but the fix backport is missing in
Ubuntu 26.04 LTS.
Reproducer:
```
ubuntu@devbox:~/firedancer$ cat <<EOF > reproducer.c
static unsigned int const enc_table_32[8][3] = {
{513735U, 77223048U, 437087610U },
{0U, 78508U, 646269101U },
{0U, 0U, 11997U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, }};
int __attribute__((noipa)) foo()
{
unsigned long intermediate[3] = {0};
for (unsigned long i = 0UL; i < 8; i++) {
intermediate[0] += 2 * (unsigned long)(enc_table_32)[i][0];
intermediate[1] += 2 * (unsigned long)(enc_table_32)[i][1];
intermediate[2] += 2 * (unsigned long)(enc_table_32)[i][2];
}
if (intermediate[0] == 0xfad8e &&
intermediate[1] == 0x9370e68 && intermediate[2] == 0x8125ca08) {
return 0;
} else {
return 1;
}
}
int main()
{
if (foo ())
__builtin_abort ();
return 0;
}
EOF
ubuntu@devbox:~/firedancer$ gcc -O3 -march=native reproducer.c -o reproducer
ubuntu@devbox:~/firedancer$ ./reproducer
Aborted (core dumped) ./reproducer
ubuntu@devbox:~/firedancer$ lsb_release -rd
Description: Ubuntu 26.04 LTS
Release: 26.04
ubuntu@devbox:~/firedancer$ apt-cache policy gcc-15
gcc-15:
Installed: 15.2.0-16ubuntu1
Candidate: 15.2.0-16ubuntu1
Version table:
*** 15.2.0-16ubuntu1 500
500 http://de.archive.ubuntu.com/ubuntu resolute/main amd64v3 Packages
100 /var/lib/dpkg/status
ubuntu@devbox:~/firedancer$ grep flags /proc/cpuinfo | head -n1
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb
rdtscp lm constant_tsc rep_good amd_lbr_v2 nopl xtopology nonstop_tsc cpuid
extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 pcid sse4_1
sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm
extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce
topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpuid_fault cpb cat_l3
cdp_l3 hw_pstate ssbd mba perfmon_v2 ibrs ibpb stibp ibrs_enhanced vmmcall
fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq
adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt
xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local
user_shstk avx_vnni avx512_bf16 clzero irperf xsaveerptr rdpru wbnoinvd
amd_ppin cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid
decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif x2avic
v_spec_ctrl vnmi avx512vbmi umip pku ospke avx512_vbmi2 gfni vaes vpclmulqdq
avx512_vnni avx512_bitalg avx512_vpopcntdq la57 rdpid bus_lock_detect movdiri
movdir64b overflow_recov succor smca fsrm avx512_vp2intersect flush_l1d
debug_swap amd_lbr_pmc_freeze
```
** Affects: gcc
Importance: Unknown
Status: Unknown
** Affects: gcc-15 (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "reproducer.c"
https://bugs.launchpad.net/bugs/2163070/+attachment/5990403/+files/reproducer.c
** Description changed:
- This GCC bug fix causes certain C code to miscompile and cause U.B.
+ This GCC bug fix causes certain C code to miscompile
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002
It was a fixed a few months ago, but the fix backport is missing in
Ubuntu 26.04 LTS.
Reproducer:
```
ubuntu@devbox:~/firedancer$ cat <<EOF > reproducer.c
- > static unsigned int const enc_table_32[8][3] = {
- {513735U, 77223048U, 437087610U },
- {0U, 78508U, 646269101U },
- {0U, 0U, 11997U, },
- {0U, 0U, 0U, },
- {0U, 0U, 0U, },
- {0U, 0U, 0U, },
- {0U, 0U, 0U, },
- {0U, 0U, 0U, }};
+ static unsigned int const enc_table_32[8][3] = {
+ {513735U, 77223048U, 437087610U },
+ {0U, 78508U, 646269101U },
+ {0U, 0U, 11997U, },
+ {0U, 0U, 0U, },
+ {0U, 0U, 0U, },
+ {0U, 0U, 0U, },
+ {0U, 0U, 0U, },
+ {0U, 0U, 0U, }};
int __attribute__((noipa)) foo()
{
- unsigned long intermediate[3] = {0};
+ unsigned long intermediate[3] = {0};
- for (unsigned long i = 0UL; i < 8; i++) {
- intermediate[0] += 2 * (unsigned long)(enc_table_32)[i][0];
- intermediate[1] += 2 * (unsigned long)(enc_table_32)[i][1];
- intermediate[2] += 2 * (unsigned long)(enc_table_32)[i][2];
- }
+ for (unsigned long i = 0UL; i < 8; i++) {
+ intermediate[0] += 2 * (unsigned long)(enc_table_32)[i][0];
+ intermediate[1] += 2 * (unsigned long)(enc_table_32)[i][1];
+ intermediate[2] += 2 * (unsigned long)(enc_table_32)[i][2];
+ }
- if (intermediate[0] == 0xfad8e &&
- intermediate[1] == 0x9370e68 && intermediate[2] == 0x8125ca08) {
- return 0;
- } else {
- return 1;
- }
+ if (intermediate[0] == 0xfad8e &&
+ intermediate[1] == 0x9370e68 && intermediate[2] == 0x8125ca08) {
+ return 0;
+ } else {
+ return 1;
+ }
}
int main()
{
- if (foo ())
- __builtin_abort ();
- return 0;
+ if (foo ())
+ __builtin_abort ();
+ return 0;
}
- > EOF
+ EOF
ubuntu@devbox:~/firedancer$ gcc -O3 -march=native reproducer.c -o reproducer
ubuntu@devbox:~/firedancer$ ./reproducer
Aborted (core dumped) ./reproducer
ubuntu@devbox:~/firedancer$ lsb_release -rd
Description: Ubuntu 26.04 LTS
Release: 26.04
ubuntu@devbox:~/firedancer$ apt-cache policy gcc-15
gcc-15:
- Installed: 15.2.0-16ubuntu1
- Candidate: 15.2.0-16ubuntu1
- Version table:
- *** 15.2.0-16ubuntu1 500
- 500 http://de.archive.ubuntu.com/ubuntu resolute/main amd64v3 Packages
- 100 /var/lib/dpkg/status
+ Installed: 15.2.0-16ubuntu1
+ Candidate: 15.2.0-16ubuntu1
+ Version table:
+ *** 15.2.0-16ubuntu1 500
+ 500 http://de.archive.ubuntu.com/ubuntu resolute/main amd64v3 Packages
+ 100 /var/lib/dpkg/status
```
** Bug watch added: GCC Bugzilla #123002
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002
** Also affects: gcc via
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002
Importance: Unknown
Status: Unknown
** Description changed:
This GCC bug fix causes certain C code to miscompile
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002
It was a fixed a few months ago, but the fix backport is missing in
Ubuntu 26.04 LTS.
Reproducer:
```
ubuntu@devbox:~/firedancer$ cat <<EOF > reproducer.c
static unsigned int const enc_table_32[8][3] = {
{513735U, 77223048U, 437087610U },
{0U, 78508U, 646269101U },
{0U, 0U, 11997U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, },
{0U, 0U, 0U, }};
int __attribute__((noipa)) foo()
{
unsigned long intermediate[3] = {0};
for (unsigned long i = 0UL; i < 8; i++) {
intermediate[0] += 2 * (unsigned long)(enc_table_32)[i][0];
intermediate[1] += 2 * (unsigned long)(enc_table_32)[i][1];
intermediate[2] += 2 * (unsigned long)(enc_table_32)[i][2];
}
if (intermediate[0] == 0xfad8e &&
intermediate[1] == 0x9370e68 && intermediate[2] == 0x8125ca08) {
return 0;
} else {
return 1;
}
}
int main()
{
if (foo ())
__builtin_abort ();
return 0;
}
EOF
ubuntu@devbox:~/firedancer$ gcc -O3 -march=native reproducer.c -o reproducer
ubuntu@devbox:~/firedancer$ ./reproducer
Aborted (core dumped) ./reproducer
ubuntu@devbox:~/firedancer$ lsb_release -rd
Description: Ubuntu 26.04 LTS
Release: 26.04
ubuntu@devbox:~/firedancer$ apt-cache policy gcc-15
gcc-15:
Installed: 15.2.0-16ubuntu1
Candidate: 15.2.0-16ubuntu1
Version table:
*** 15.2.0-16ubuntu1 500
500 http://de.archive.ubuntu.com/ubuntu resolute/main amd64v3 Packages
100 /var/lib/dpkg/status
+ ubuntu@devbox:~/firedancer$ grep flags /proc/cpuinfo | head -n1
+ flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb
rdtscp lm constant_tsc rep_good amd_lbr_v2 nopl xtopology nonstop_tsc cpuid
extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 pcid sse4_1
sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm
extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce
topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpuid_fault cpb cat_l3
cdp_l3 hw_pstate ssbd mba perfmon_v2 ibrs ibpb stibp ibrs_enhanced vmmcall
fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq
adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt
xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local
user_shstk avx_vnni avx512_bf16 clzero irperf xsaveerptr rdpru wbnoinvd
amd_ppin cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid
decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif x2avic
v_spec_ctrl vnmi avx512vbmi umip pku ospke avx512_vbmi2 gfni vaes vpclmulqdq
avx512_vnni avx512_bitalg avx512_vpopcntdq la57 rdpid bus_lock_detect movdiri
movdir64b overflow_recov succor smca fsrm avx512_vp2intersect flush_l1d
debug_swap amd_lbr_pmc_freeze
```
--
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https://bugs.launchpad.net/bugs/2163070
Title:
Miscompile in GCC 15.2.0 (x86)
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